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The following is part 1 of a nice intro to CD technology written by Andy Poggio in 1988. It appears here in its original form.

CD Summary Introduction

As requested by many people, I will post this CD Summary over the next several days in five parts of which this is the first. I received requests from, comp.ivideodisc, and – so I will post it to all these groups. I'm not sure that it is appropriate for but I DID receive multiple requests to post it there.

The summary is somewhat technical but more important it is factual: I wrote it after reading the original CD standards documents available from Sony or Philips to CD licensees. If you are interested in the standards documents, you need to contact them directly – sorry, I don't have a specific contact or phone number.

I do work for Apple but this summary contains a minimum of Apple references. I hope everyone agrees that the result is in keeping with net policy on the matter.


CD Summary Part 1

CD-ROM Technical Summary

From Plastic Pits to "Fantasia"
                                             Andy Poggio
                                             March, 1988


This summary describes how information is encoded on Compact Disc (CD) beginning with the physical pits and going up through higher levels of data encoding to the structured multimedia information that is possible with programs like HyperCard. This discussion is much broader than any single standards document, e.g. the CD-Audio Red Book, while omitting much of the detail needed only by drive manufacturers.

Salient Characteristics

1. High information density – With the density achievable using optical encoding, the CD can contain some 540 megabytes of data on a disc less than five inches in diameter.

2. Low unit cost – Because CDs are manufactured by a well-developed process similar to that used to stamp out LP records, unit cost in large quantities is less than two dollars.

3. Read only medium – CD-ROM is read only; it cannot be written on or erased. It is an electronic publishing, distribution, and access medium; it cannot replace magnetic disks.

4. Modest random access performance – Due to optical read head mass and data encoding methods, random access ("seek time") performance of CD is better than floppies but not as good as magnetic hard disks.

5. Robust, removable medium – The CD itself is comprised mostly of, and completely coated by, durable plastic. This fact and the data encoding method allow the CD to be resistant to scratches and other handling damage. Media lifetime is expected to be long, well beyond that of magnetic media such as tape. In addition, the optical servo scanning mechanism allows CDs to be removed from their drives.

6. Multimedia storage – Because all CD data is stored digitally, it is inherently multimedia in that it can store text, images, graphics, sound, and any other information expressed in digital form. Its only limit in this area is the rate at which data can be read from the disc, currently about 150 KBytes/second. This is sufficient for all but uncompressed, full motion color video.

CD Summary Part 2

CD Data Hierarchy

Storing data on a CD may be thought of as occurring through a data encoding hierarchy with each level built upon the previous one. At the lowest level, data is physically stored as pits on the disc. It is actually encoded by several low-level mechanisms to provide high storage density and reliable data recovery. At the next level, it organized into tracks which may be digital audio or CD-ROM. The High Sierra specification then defines a file system built on CD-ROM tracks. Finally, applications like HyperCard specify a content format for files.

The Physical Medium

The Compact Disc itself is a thin plastic disk some 12 cm. in diameter. Information is encoded in a plastic-encased spiral track contained on the top of the disk. The spiral track is read optically by a noncontact head which scans approximately radially as the disk spins just above it. The spiral is scanned at a constant linear velocity thus assuring a constant data rate. This requires the disc to rotate at a decreasing rate as the spiral is scanned from its beginning near the center of the disc to its end near the disc circumference.

The spiral track contains shallow depressions, called pits, in a reflective layer. Binary information is encoded by the lengths of these pits and the lengths of the areas between them, called land. During reading, a low power laser beam from the optical head is focused on the spiral layer and is reflected back into the head. Due to the optical characteristics of the plastic disc and the wavelength of light used, the quantity of reflected light varies depending on whether the beam is on land or on a pit. The modulated, reflected light is converted to a radio frequency, raw data signal by a photodetector in the optical head.

Low-level Data Encoding

To ensure accurate recovery, the disc data must be encoded to optimize the analog-to-digital conversion process that the radio frequency signal must undergo. Goals of the low level data encoding include:

1. High information density. This requires encoding that makes the best possible use of the high, but limited, resolution of the laser beam and read head optics.

2. Minimum intersymbol interference. This requires making the minimum run length, i.e. the minimum number of consecutive zero bits or one bits, as large as possible.

3. Self-clocking. To avoid a separate timing track, the data should be encoded so as to allow the clock signal to be regenerated from the data signal. This requires limiting the maximum run length of the data so that data transitions will regenerate the clock.

4. Low digital sum value (the number of one bits minus the number of zero bits). This minimizes the low frequency and DC content of the data signal which permits optimal servo system operation.

A straightforward encoding would be to simply to encode zero bits as land and one bits as pits. However, this does not meet goal (1) as well as the encoding scheme actually used. The current CD scheme encodes one bits as transitions from pit to land or land to pit and zero bits as constant pit or constant land.

To meet goals (2) to (4), it is not possible to encode arbitrary binary data. For example, the integer 0 expressed as thirty-two bits of zero would have too long a run length to satisfy goal (3). To accommodate these goals, each eight-bit byte of actual data is encoded as fourteen bits of channel data. There are many more combinations of fourteen bits (16,384) than there are of eight bits (256). To encode the eight-bit combinations, 256 combinations of fourteen bits are chosen that meet the goals. This encoding is referred to as Eight-to-Fourteen Modulation (EFM) coding.

If fourteen channel bits were concatenated with another set of fourteen channel bits, once again the above goals may not be met. To avoid this possibility, three merging bits are included between each set of fourteen channel bits. These merging bits carry no information but are chosen to limit run length, keep data signal DC content low, etc. Thus, an eight bit byte of actual data is encoded into a total of seventeen channel bits: fourteen EFM bits and three merging bits.

To achieve a reliable self-clocking system, periodic synchronization is necessary. Thus, data is broken up into individual frames each beginning with a synchronization pattern. Each frame also contains twenty-four data bytes, eight error correction bytes, a control and display byte (carrying the subcoding channels), and merging bits separating them all. Each frame is arranged as follows:

Sync Pattern24 + 3channel bits Control and Display byte14 + 3 Data bytes12 * (14 + 3) Error Correction bytes 4 * (14 + 3) Data bytes12 * (14 + 3) Error Correction bytes 4 * (14 + 3)

TOTAL588channel bits

Thus, 192 actual data bits (24 bytes) are encoded as 588 channel bits.

Editorial: A CD physically has a single spiral track about 3 miles long. CDs spin at about 500 RPM when reading near the center down to about 250 RPM when reading near the circumference.

Disc with a 'c' or disk with a 'k'? A usage has emerged for these terms: disk is used for eraseable disks (e.g. magnetic disks) while disc is used for read-only (e.g. CD-ROM discs). One would presumably call a frisbee a disc.


CD Summary Part 3

First Level Error Correction

Data errors can arise from production defects in the disk itself, defects arising from subsequent damage to the disk, or jarring during reading. A significant characteristic of these errors is that they often occur in long bursts. This could be due, for example, to a relatively wide mark on the disc that is opaque to the laser beam used to read the disc. A system with two logical components called the Cross Interleave Reed-Solomon Coding (CIRC) is employed for error correction. The cross interleave component breaks up the long error bursts into many short errors; the Reed-Solomon component provides the error correction.

As each frame is read from the disc, it is first decoded from fourteen channel bits (the three merging bits are ignored) into eight-bit data bytes. Then, the bytes from each frame (twenty-four data bytes and eight error correction bytes) are passed to the first Reed-Solomon decoder which uses four of the error correction bytes and is able to correct one byte in error out of the 32. If there are no uncorrectable errors, the data is simply passed along. If there are errors, the data is marked as being in error at this stage of decoding.

The twenty-four data bytes and four remaining error correction bytes are then passed through unequal delays before going through another Reed-Solomon decoder. These unequal delays result in an interleaving of the data that spreads long error bursts among many different passes through the second decoder. The delays are such that error bursts up to 450 bytes long can be completely corrected. The second Reed-Solomon decoder uses the last four error correction bytes to correct any remaining errors in the twenty-four data bytes. At this point, the data goes through a de-interleaving process to restore the correct byte order.

Subcoding Channels and Blocks

The eight-bit control and display byte in each frame carries the subcoding channels. A subcoding block consists of 98 subcoding bytes, and thus 98 of the 588-bit frames. A block then can contain 2352 bytes of data. Seventy-five blocks are read each second. With this information, it is now straightforward to calculate that the CD data rate is in fact correct for CD digital audio (CD-DA):

Required CD digital audio data rate: 44.1 K samples per second * 16 bits per sample * 2 channels = 1,411,200 bits/sec.

CD data rate: 8 bits per byte * 24 bytes per frame * 98 frames per subcoding block * 75 subcoding blocks per second = 1,411,200 bits/sec.

The eight subcoding channels are labeled P through W and are encoded one bit for each channel in a control and display byte. Channel P is used as a simple music track separator. Channel Q is used for control purposes and encodes information like track number, track type, and location (minute, second, and frame number). During the lead-in track of the disc, channel Q encodes a table of contents for the disk giving track number and starting location. Standards have been proposed that would use the remaining channels for line graphics and ASCII character strings, but these are seldom used.

Track Types

Tracks can have two types as specified in the control bit field of subchannel Q. The first type is CD digital audio (CD-DA) tracks. The two-channel audio is sampled at 44.1 Khz with sixteen bit linear sampling encoded as twos complement numbers. The sixteen bit samples are separated into two eight-bit bytes; the bytes from each channel alternate on the disc. Variations for audio tracks include pre-emphasis and four track recording.

The other type of track specified by the subchannel Q control bit field is the data track. These must conform to the CD-ROM standard described below. In general, a disc can have a mix of CD digital audio tracks and a CD-ROM track, but the CD-ROM track must come first.

Editorial: This first level error correction (the only type used for CD Audio data) is extremely powerful. The CD specification allows for discs to have up to 220 raw errors per second. Every one of these errors is (almost always) perfectly corrected by the CIRC scheme for a net error rate of zero. For example, our tests using Apple's CD-ROM drive (which also plays audio) show that raw error rates are around 50-100 per second these days. Of course, these are perfectly corrected, meaning that the original data is perfectly recovered. We have tested flawed discs with raw rates up to 300 per second. Net errors on all of these discs? Zero! I would expect a typical audio CD player to perform similarly. Thus I expect this raw error rate to have no audible consequences.

So why did I say "almost always" corrected above? Because a sufficiently bad flaw may produce uncorrectable errors. These very unusual errors are "concealed" by the player rather than corrected. Note that this concealment is likely to be less noticeable than even a single scratch on an LP. Such a flaw might be a really opaque finger smudge; CDs do merit careful handling. On the two (and only two) occasions I have found these, I simply sprayed on a little Windex glass cleaner and wiped it off using radial strokes. This restored the CDs to zero net errors.

One can argue about the quality of the process of conversion of analog music to and from digital representation, but in the digital domain CDs are really very, very good.

CD Summary Part 4

CD-ROM Data Tracks

Each CD-ROM data track is divided into individually addressable blocks of 2352 data bytes, i.e. one subcoding block or 98 frames. A header in each block contains the block address and the mode of the block. The block address is identical to the encoding of minute, second, and frame number in subcode channel Q. The modes defined in the CD-ROM specification are:

Mode 0 – all data bytes are zero.

Mode 1 – (CD-ROM Data): Sync Field - 12 bytes Header Field - 4 User Data Field - 2048 Error Detection Code - 4 Reserved - 8 Error Correction - 276

Mode 2 – (CD Audio or Other Data): Sync Field - 12 bytes Header Field - 4 User Data Field - 2048 Auxiliary Data Field - 288

Thus, mode 1 defines separately addressable, physical 2K byte data blocks making CD-ROM look at this level very similar to other digital mass storage devices.

Second Level Error Correction

An uncorrected error in audio data typically results in a brief, often inaudible click during listening at worst. An uncorrected error in other kinds of data, for example program code, may render a CD unusable. For this reason, CD-ROM defines a second level of error detection and error correction (EDC/ECC) for mode 1 data. The information for the EDC/ECC occupies most of the auxiliary data field.

The error detection code is a cyclic redundancy check (CRC) on the sync, header, and user data. It occupies the first four bytes of the auxiliary data field and provides a very high probability that uncorrected errors will be detected. The error correction code is essentially the same as the first level error correction in that interleaving and Reed-Solomon coding are used. It occupies the final 276 bytes of the auxiliary data field.

Editorial: This extra level of error correction for CD-ROM blocks is one of the many reasons that CD-ROM drives are much more expensive than consumer audio players. To perform this error correction quickly requires substantial extra computing power (sometimes a dedicated microprocessor) in the drive.

This is also one reason that consumer players like the Magnavoxes which claim to be CD-ROM compatible (with their digital output jack on the back) are useless for that purpose. They have no way of dealing with the CD-ROM error correction. They also have no way for a computer to tell them where to seek.

Another reason that CD-ROM drives are more expensive is that they are built to be a computer peripheral rather than a consumer device, i.e. like a combination race car/truck rather than a family sedan. One story, probably apocryphal but not far from the truth, has it that a major Japanese manufacturer tested some consumer audio players to simulate computer use: they made them seek (move the optical head) from the inside of the CD to the outside and back again. These are called maximum seeks. The story says they managed to do this for about 24 hours before they broke down. A CD-ROM drive needs to be several orders of magnitude more robust. Fast and strong don't come cheap.

CD Summary Part 5

The High Sierra File System Standard

Built on top of the addressable 2K blocks that the CD-ROM specification defines, the next higher level of data encoding is a file system that permits logical organization of the data on the CD. This can be a native file system like the Macintosh Hierarchical File System (HFS). Another alternative is the High Sierra (also known as the ISO 9660) file standard, recently approved by the National Information Standards Organization (NISO) and the International Standards Organization (ISO), which defines a file system carefully tuned to CD characteristics. In particular:

1. CDs have modest seek time and high capacity. As a result, the High Sierra standard makes tradeoffs that reduce the number of seeks needed to read a file at the expense of space efficiency.

2. CDs are read-only. Thus, concerns like space allocation, file deletion, and the like are not addressed in the specification.

For High Sierra file systems, each individual CD is a volume. Several CDs may be grouped together in a volume set and there is a mechanism for subsequent volumes in a set to update preceding ones. Volumes can contain standard file structures, coded character set file structures for character encoding other than ASCII, or boot records. Boot records can contain either data or program code that may be needed by systems or applications.

High Sierra Directories and Files

The file system is a hierarchical one in which directories may contain files or other directories. Each volume has a root directory which serves as an ancestor to all other directories or files in the volume. This dictates an overall tree structure for the volume.

A typical disadvantage in hierarchical systems is that to read a file (which must be a leaf of the hierarchy tree) given its full path name, it is necessary to begin at the root directory and search through each of its ancestral directories until the entry for the file is found. For example, given the path name "Wine Regions:America:California:Mendocino", three directories (the first three components of the path name) would need to be searched. Typically, a separate seek would be required for each directory. This would result in relatively poor performance.

To avoid this, High Sierra specifies that each volume contain a path table in addition to its directories and files. The path table describes the directory hierarchy in a compact form that may be cached in computer memory for optimum performance. The path table contains entries for the volume's directories in a breadth-first order; directories with a common parent are listed in lexicographic order. Each entry contains only the location of the directory it describes, its name, and the location in the path table of its parent. This mechanism allows any directory to be accessed with only a single CD seek.

Directories contain more detailed information than the path table. Each directory entry contains:

Directory or file location. File length. Date and time of creation. Name of the file. Flags: Whether the entry is for a file or a directory. Whether or not it is an associated file. Whether or not it has records. Whether or not it has read protection. Whether or not it has subsequent extents. Interleave structure of the file.

Interleaving may be used, for example, to meet realtime requirements for multiple files whose contents must be presented simultaneously. This would happen if a file containing graphic images were interleaved with a file containing compressed sound that describes the images.

Files themselves are recorded in contiguous (or interleaved) blocks on the disc. The read-only nature of CD permits this contiguous recording in a straightforward manner. A file may also be recorded in a series of noncontiguous extents with a directory entry for each extent.

The specification does not favor any particular computer architecture. In particular all significant, multibyte numbers are recorded twice, once with the most significant byte first and once with the least significant byte first.

Multimedia Information

Using the file system are applications that create and portray multimedia information. While it is true that a CD can store anything that a magnetic disk can store (and usually much more of it), CDs will be used more for storing information than for storing programs. It is the very large storage capacity of CDs coupled with their low cost that opens up the possibilities for interactive, multimedia information to be used in a multitude of ways.

Programs like HyperCard, with it's ease of authoring and broad extensibility, are very useful for this purpose. Hypercard stacks, with related information such as color images and sound, can be easily and inexpensively stored on CDs despite their possibly very large size.

Editorial: The High Sierra file system gets its name from the location of the first meeting on it: the High Sierra Hotel at Lake Tahoe. It is much more commonly referred to as ISO 9660, though the two specifications are slightly different.

It has gotten very easy and inexpensive to make a CD-ROM disc (or audio CD). For example, you can now take a Macintosh hard disk and send it with $1500 to one of several CD pressers. They will send you back your hard disk and 100 CDs with exactly the same content as what's on your disk. This is the easy way to make CDs with capacity up to the size of your hard disk (Apple's go up to 160 megabytes). True, this is not a full CD but CDs don't need to be full. If you have just 10 megabytes and need 100 copies, CDs may be the best way to go.

If you are buying a CD-ROM drive, there are several factors you might consider in making your choice. Two factors NOT to consider are capacity and data rate. The capacity of all CD-ROM drives is determined solely by the CD they are reading. Though you will see a range of numbers in manufacturers' specs (e.g. 540, 550, 600, and 650 Mbytes), any drive can read any disc and so they are all fundamentally the same. All CD-ROM drives read data at a net 150 Kbytes/sec for CD-ROM data. Other data rates you may see may include error correction data (not included in the net rate) or may be a mode 2 data rate (faster than mode 1). All drives will be the same in all of these specs.

[ Editorial: The last paragraph is wrong on both points. This may have been true in 1988, when this article was written, but is no longer true today (in 1992). A few drives cannot read CDROMs with more than about 620 megabytes on them. There is a huge variation in speed. Today only the slowest drives read at 150 kb/sec. Most read at least 300 and at least one (the Pioneer DRM-600X) reads at 600 kb/sec. ]

Reprinted from Atari Explorer Online Volume 2, Issue 1, Januari 1993.

||| The ALBERT File: CD-ROM & Photo CD …… Coming to an Atari near you ||| By: Albert Dayes / | \ CompuServe: 70007,3615 GEnie: AEO.1

  1. ——————————————————————–

/* Title: CD.DOC Created: December 10, 1992 Last Modified: December 31, 1992 Purpose: A Guide to Optical Storage with a special focus on CD-ROM and Kodak's Photo CD on the Atari platform. Author: Albert Dayes Legal Notes: Copyright 1992 Albert Dayes, All Rights Reserved Some portions Copyright 1992 Rich Bowers, used by permission. Version: 1.0 */

         CD-ROM on the Atari Platform NOW!

Atari owners have been waiting with baited breath for CD-ROM to arrive on the Atari platform. Actually the CD-ROM portion has been around for quite a while but now you can add Photo CD to the long list of tools available on the Atari ST, TT030, and Falcon030.

This is a guide to CD-ROM in general and what it all means to the user. Its purpose is to go beyond the endless lists of terms on optical media and CD-ROM and explain how it can work for you. Included is a glossary of terms so one can have something to refer to when an unknown term appears.

Thanks are in order to several people but one in particular is Rich Bowers (CO-SYSOP on CD-ROM forum on COMPUSERVE) who provided answers to quite a few questions in this document. He does an outstanding job as you will notice when you start reading it.

/*/ Special Thanks to: Steve Luper = Sysop of the CD-ROM forum on COMPUSERVE (GO CD-ROM) Rich Bowers = Co-Sysop of the CD-ROM forum on COMPUSERVE and Executive Director of Optical Publishing Association (OPA). Rich willingly provided answers to some of the questions in this document; specifically questions: A, B, C, D, E, which are Copyright 1992 Rich Bowers. Paul McAfee = of Kodak (Press Relations Manager for Photo CD) - for all his help with my Photo CD questions. Also for all of Kodak's Press Releases dealing with Photo CD. Scott Brownstein = Manager of Advanced Projects at Kodak - for answering questions on technical details on CD technology and Photo CD. Additional Thanks: Ron Luks = Chief Sysop of the Atari forums on COMPUSERVE (GO ATARI) Paul Wisotzke = of Kodak Information Center (KIC) Joel White = of Kodak Information Center (KIC) // TABLE OF CONTENTS A) What is CD-ROM? B) What is the difference between "disc" and "disk"? C) How standardized is CD-ROM? D) What is SCSI and why is it important to CD-ROM? E) How is CD-ROM related to laserdisc (videodisc)? F) What are the CD-ROM standards? G) What benefit is CD-ROM to me? H) How much does it cost to make my own CD-ROM disc? I) What is Kodak's Photo CD? J) What is multi-session and why is it important to Photo CD? K) Summary of an interview Scott Brownstein - manager of Advanced Projects at Kodak. L) Which is the best CD-ROM drive to buy for use on the Atari? CONTACTS for ATARI Related CD-ROM and/or PHOTO CD products. ISO-9660 filesystem made EASY MULTI-SESSION made EASY Making My OWN CD-ROM made EASY An Atari Dream CD-ROM GLOSSARY OF TERMS CD-ROM DRIVE MANUFACTURERS SOURCES OF INFORMATION ON OPTICAL MEDIA and SPECIFICATIONS /*/ –==– A) What is CD-ROM? Physically, CD-ROM is the same compact disc that has become the standard for the delivery of music. It is a plastic disc, 4-3/4" (12cm) in diameter, on which data is recorded digitally. There is also a 3-1/2" (8cm) form factor, equivalent to the mini-disc music product (although this size is currently used only in Sony's Data DiscMan portable reader). Because compact disc is a digital medium, it is a natural for delivery of information of a variety of types - text, photos, audio, computer-generated graphics, video and software - to a computer host. CD-ROM has many unique features that suit it to information delivery. It has a capacity of approximately 650 million characters (about 200 million characters for the mini-disc). This capacity is analogous to any number of measures. It is equivalent to over 1500 high-density floppies (1.44 megabyte disk size), or over 200,000 pages of printed text. By using a lower sampling frequency for recording audio, it can hold many hours of sound. It can hold upwards of 10,000 high quality photographs. By using compression and decompression techniques (in partnership with the host computer), these numbers can be greatly increased. It is a very durable delivery medium. It is not indestructible, but it is not subject to magnetic fields as hard disks are, and it can be mailed with minimal protection. The disc itself weighs only an ounce or two, and thus is highly portable. Technical standards enable a CD-ROM to be "portable," in a computer sense, across many types of systems. Because compact discs are mastered and inexpensively replicated in quantity, CD-ROM is an ideal medium for "publishing" many copies of large volumes of information. Because the discs are digital and have a high capacity, they are amenable to entirely new categories of products - such as multimedia - which have not been "published" in the past, because there was no practical means to do so. Thus there are large databases that have formerly been accessible only online being published, in whole or in part, on CD-ROM. We see multimedia presentations, which formerly were only accessible from large magnetic discs, being packaged and distributed like other publications. CD-ROM has inspired new methods for the delivery of existing materials, it has inspired the creation of radically new materials, and it has inspired a complete re-thinking of traditional publishing and distribution processes. For this reason, we see CD-ROM as the catalyst and the means for a "revolution" in publishing. Compact disc was created and defined in a series of proprietary standards by a joint effort of Sony and Philips. Compact disc-audio was introduced as a commercial product in 1982. The first CD-ROM applications were introduced for sale in late 1985. CD-I was announced in 1986, the first commercial products were sold in the fall of 1991. CDTV was first sold in the spring of 1991. The MPC specification was introduced in 1991, and the first MPC-compliant upgrade kits and titles were launched in late 1991. Of course, there are new CD-ROM based devices coming from Sony (via the handheld Data Discman and the so-called Bookman), Tandy (VIS) and cartridge-based game systems producers like Sega, NEC and Nintendo. CD-ROM differs from CD-audio in that certain data are added to meet the needs of computer operating systems, and to assure that the data you receive are the same as the data originally recorded. To meet the needs of a computer's operating system, a header is required that describes the nature and location of the data on the disc. This is called a volume-table-of contents, or VTOC in computer-ese. The integrity of the data is assured through the use of multiple layers of error-correction codes, which further distinguish CD-ROM from CD-audio. The structure and use of these components are mandated by standards such as the Yellow Book (which defines the recording of data for computer use, extending the CD-audio standard described in the Red Book), and ISO 9660, an international standard that defines the VTOC. Within these constraints, there are many ways to deliver information for specific platforms and applications. These differing methods have lead to the proliferation of "CD-ROM formats" - such as CD-ROM-XA, CD-I and so forth. These are described in detail below. However, all formats conform first to the CD-audio standard, second to the CD-ROM standard, and third to the extended specifications required for each format. In short, CD-I is a format of CD-ROM, CDTV is a format of CD-ROM, etc. CD-ROM requires a computer to read, interpret and display data, and to deal with the interactive nature of CD-ROM access and use. The initial products were exclusively computer host-based: the drive is attached as a peripheral to a personal computer. In recent years, a new category of products has emerged: the so-called "information appliances," such as CD-I, VIS, Data Discman, etc. These products also use computers, but the computer-ness is embedded in the use of the product. The technical aspects of many of these products are described below. –==– B) What is the difference between "disc" and "disk"? The convention is that "disc" refers to optical media, while "disk" refers to magnetic media. The distinction is important, because the different spellings signify very different products. Most trade media seem to be oblivious to the distinction. By the way, the absolutely correct way of referring to CDROM is "CD-ROM." This author and others often remove the hyphen because a) it does not change the meaning and b) it is easier to type. CD-ROM should not be shortened to "CDR" because CD-R refers to compact disc-recordable systems, or CD-Write Once. –==– C) How standardized is CD-ROM? CD-ROM is one of the most thoroughly standardized computer sub-systems in the history of the business. The medium is standard, and the drives that read the medium are defined by standards. The format of the header which enables cross-platform access to data - ISO 9660 - is standardized. Not all is perfect, however. CD-ROM developers must do business in the real world comprised of a variety of computer platforms, operating systems, and other factors. So the information content on a CD-ROM remains - to some extent - dependent on the system which will access and use the data. –==– D) What is SCSI, and why is it important to CD-ROM? The Small Computer System Interface (SCSI - generally pronounced "scuzzee"), is a standard which permits the connection of up to 7 different devices to the host computer. Each device still requires its own driver software. The use of SCSI requires an interface board inserted in an expansion slot of a PC. Macintosh and UNIX systems are natively SCSI-based. One advantage of SCSI is that expansion slots are conserved - instead of a proprietary interface board required for each device, several can share the same interface. Devices such as scanners, printers, hard drives, CD-R drives like Philips CDD-521, MO drives, WORM drives, and some network cards (usually ethernet), can use SCSI in addition to CD-ROM drives. Virtually all CD-ROM drive manufacturers have one or more models that are SCSI compatible. In most cases, the consumer has a choice of acquiring the interface board from the CD-ROM drive vendor, or using a board from a third party. At the risk of offending some vendors by exclusion, note that interfaces from Adaptec, UltraStor and Future Domain receive many comments on the CD-ROM Forum. A new variation on SCSI has emerged. The original standard, now called SCSI-1, has been enhanced with a new specification called SCSI-2. SCSI-2 has standardized audio commands for CD-ROM drives. So using a SCSI-2 "play" command will work on all SCSI-2 CD-ROM drives, eliminating the need for unique audio device drivers for each CD-ROM drive. SCSI-2 is backwardly compatible with SCSI-1, so a SCSI-1 device will work with a SCSI-2 interface board. In addition, SCSI-2 will offer faster transfer speed for devices that can support it, and the capability to transfer 16- and 32-bit paths in addition to the normal 8-bits. Standard SCSI connectors have 50 pins, a new wide SCSI has a 68-pin connector. SCSI-2 has not been formally approved yet, although some vendors are offering products with these features. (My thanks to Albert Dayes for providing the majority of this data.) NOTE: The Atari TT is SCSI based and the Atari Falcon030 is SCSI-2 based, and with Atari and third party host adapters like ICD one can have SCSI-1 or SCSI-2 adapters available for use on the Atari ST series of computers. –==– E) How is CD-ROM related to laserdisc (videodisc)? In the mid-1970's a number of companies introduced a 12" disc product which could deliver movies and other graphical/video content superior to that of videotape formats. What we know now as the laserdisc, or videodisc, has been up, and it has been down, in terms of market acceptance. It has been of consistent interest for training and educational purposes, because it provided an "interactive" capability for the use of video material that tape does not provide. Recently, videodisc has seen a resurgence in the consumer marketplace. Laserdisc is an analog format: the data are recorded on the disc just as in any other analog medium like video or audio tape. CD-ROM is a digital format. Laserdisc gives a superior quality video picture and high quality sound. Laserdisc is not a good medium for delivery of text, software or manipulatable data elements. Digital video technology is still being perfected, but no one would claim that CD-ROM can deliver as a good a tv picture as laserdisc. The advantage CD-ROM brings to the table is the ability to mix and match a wide variety of data elements through retrieval or authoring software. If the sole requirement of the consumer is high-quality video, then laserdisc is the right product to buy. If, however, the requirement is for random access to large volumes of mixed-format data, a high degree of interactivity, or converging published data with other computer applications, then CD-ROM is the right product. It is this flexibility (albeit with limitations in the video arena) that has captured the attention of many new publishers. –==– F) What are the CD-ROM standards? The standards have two levels, the physical and logical level. The physical defines how the actual disc is made (size, material, etc). The logical defines how a device driver or operating system will view the data that is placed on the disc. There is a broad standard that gives the physical characteristics of the disc and this is called the "Yellow Book." The "Yellow Book" defines all the physical requirements for any CD-ROM disc. The "Yellow Book" has everything basically that the "Red Book" has and more. Audio CDs are defined by the "Red Book," and the "Yellow Book" allows for CD-ROM to have either data or audio tracks or a hybrid that allows for both types of tracks on a CD-ROM. This hybrid is usually referred to as mixed mode. The logical format one can also think of as the filesystem of the CD-ROM. In the 1986 the High Sierra format was made and when the ISO (International Standards Organization) modified it became the ISO-9660 standard. This ISO-9660 standard is very important since it allows for any type of system to be able to read it. Platform independence was one of the very important features of the ISO-9660 standard. One does notice that it has a strong MS-DOS influence in its overall design and in some of the limits. It is important to note that logical format can be any filesystem and does not necessarily mean ISO-9660. For example some discs are in Apple Macintosh HFS (Hierarchical File System) rather than ISO-9660. CD-ROM/XA allows everything listed above and it added a compressed audio capability. Also, the layouts of the tracks on the physical disc have been modified to allow for more specific track information. CD-I and Photo CD are built on top of this enhancement to CD-ROM. The audio is ADPCM and it is interleaved with data. This allows for nicely synchronized audio without taking away CPU time. It is not used very much currently but this may change in the future. Rich Bowers, Executive Director of the OPA sums it up nicely. Its primary purpose was to interleave audio with other data, in effect to synchronize audio with a visual presentation. Think in terms of making the sound come out in synch with the lips moving. When you consider it, there are basically two kinds of data: those which are time-sequence dependent and those which are not. A database retrieval or the presentation of a single graphic is independent of other data from a time perspective. Audio is absolutely tied to a time-sequence. Video data is also dependent on time-sequencing, although we have some freedom in representing motion because the psychological phenomenon that lets us fill in the blanks in our minds, in essence to see things that aren't there. Audio is less flexible that way. XA is a physical means of storing data that depends on the time-sequencing of related data. A new standard called HyTime (about which I hope to have a file uploaded soon) is a production technique for dealing with time-sequenced data, based on the SGML mark-up strategy. Rock Ridge extensions to the ISO-9660 standard allow all the features of the UNIX filesystem to be used. These extra information is stored the System Use fields defined in the ISO-9660 standard. The information that is stored there for UNIX/POSIX include uid, gid, permissions, file mode bits, file types, setuid, setgid, sticky bit, file links, device nodes, symbolic links, POSIX filenames, reconstruction of deep directories and time stamps. –==– G) What benefit is CD-ROM to me? The benefits can be quite numerous once you start listing all of them. First we can discuss some of the possible uses for CD-ROMs. Desk Top Publishing = Large amount of clip art, fonts and images can be & Graphic Designers found for relatively low cost from many vendors. Kodak Photo CD's can have a great impact in this area as well. Musicians & = CD-ROM discs can hold a huge amount of different Audio Engineers samples and sound effects covering a large range of topics at a very reasonable cost. Generic sequences for MIDI will also be available in the future. Writers = Reference materials including dictionaries, quotations and complete works by a large variety of authors on one disc. Programmers = Walnut Creek has 600 megabytes of source code for under $40. Being able to store all that source code in a concise place is a major benefit of CD-ROM. One can get C source code which includes a part of BSD UNIX (including the networking code), X-Windows (X11R5), and entire GNU source code for under $50. The entire library of the C USERS JOURNAL plus all of the program source code listings in the magazine (since 1987) for $50. Marketing Managers = Census data can be purchased on CD-ROM in a raw ascii data format and can be loaded into a database or spreadsheet for endless "what if" type of manipulation. Also there are many CD-ROMs that target specific geographical regions that can be very useful for niche markets. Space Exploration = One can purchase CD-ROMs from the different space missions for under $10 each from the NASA Space Science Data Center. Geology and = The US Geological survey has quite a few CD-ROMs Mapping consisting of the entire USA or specific geographical regions for quite a low cost. One interested in graphics could generate some nice 3D graphic models. Games = Games are coming to CD-ROM slowly but surely. Health Providers = Important Medical Journals, and medical research papers are available now on CD-ROM. Lawyers = There are a few CD-ROMs of all the laws for specific states and even compilations from West Publishing, one of the largest law publishers which also includes an on-line service for lawyers. Optical Publishing = Custom designed CD-ROMs that contain complete specifications and documents is a very strong growing area of the CD-ROM market. This also includes multi-media titles as well and much more. Education = Interactive learning using multi-media on CD-ROMs. Research papers and much more are available in this exploding market. Religion = The Bible (in many versions), Koran and many other works from different religions all on one disc. Family Album = Store all the family pictures on a single disc using Photo CD. Anyone = Archiving important data for later retrieval. This data can be anything: financial, marketing, C source code, software, games, papers, audio, etc. General = There is a tremendous amount of information on CD-ROM discs in just plain ASCII format that anyone can use with their computer. Just import it into a word processor, spreadsheet or database and there are endless possibilities. One could go on and on about the possibilities. What types are available for the Atari currently? All discs that are ISO-9660 compliant and contain raw data, sound, clip art, images, etc, can be used on the Atari immediately. Currently there are not any CD-ROMs specifically designed for the Atari ST except for a couple that include many different shareware programs. You can not run programs on CD-ROMs designed for other platforms like the IBM PC or the MAC; it just like attempting to run a PC program from your Atari… it won't work. This will change once more people get CD-ROM drives on the Atari and start asking for titles. The Atari Falcon030 and the TT030 have both been to shown to work with Kodak's Photo CD at the recent Fall 1992 Comdex show. It was working directly with an application (a DeskTop Publishing program) called Calamus SL. The key here is the hardware and software is available to use CD-ROMs on the Atari is available NOW! Both Atari and ICD have drivers available that work with SCSI CD-ROM drives. –==– H) How much does it cost to produce my own CD-ROM disc? One can take 600 megabytes of a hard disk and save it to tape, then send to some specific publishers and they will convert it to a single CD-ROM for $200. One could probably use Beckemeyer's SCSI TAPE KIT or Oregon Research Associates Diamond Back III to perform that operation. One should check to be sure that the publisher can handle the current tape format. The format usually used is TAR. TAR allows for files to be backed up and restored on many different platforms. In addition, it can split large files and each tape is independent of the other tapes when it comes to restoration. If one wants to be able to create One-Offs or CD-WO discs one needs to spend around $12,000 for everything one would need. Then you can create your own discs at your convenience and then send it off to the duplicator for more copies when you need to. The CD-WO media is under $50 so it isn't too expensive from a media point of view. The most expensive part of the creating One-Offs is CD-Writer itself which ranges from around $7000 and up depending on the features available. These devices are usually SCSI devices and create a CD disc (audio or data) in about 30 to 70 minutes on average. The software to create a disc image (usually called the pre-mastering phase) is around $2500 and up. Plus a computer to handle all of that can be $3000 and up. Prices are dropping all the time so it might now be too long before many people have personal CD-Writers. –==– I) What is Kodak's Photo CD? Is a new standard based upon an extension CD-ROM/XA specification since it adds additional information at the track level. This new format is called the CD-Bridge format and it is what Kodak's Photo CD is based on. The Photo CD system, jointly developed by Eastman Kodak Company and Philips stores 35-mm photographs as well as text, graphics and sound on compact discs. It offers several benefits to consumers and professionals: * rapid retrieval and display of images * consistent and optimum image quality * access to powerful image manipulation * access to high-quality, continuous tone printing * support for a wide range of colors; * image duplication without degradation * support for current and future television formats How much does it cost to get my film on a Photo CD? The average cost is around $24 for an average roll of film. One gets the negatives, prints and a Photo CD. One should contact their local photofinisher or Kodak for the location of the one in your area. The picture resolutions range from 128 x 192 to 2048 x 3072 and all 5 resolutions are in 24-bit color. How big is image of the highest resolution? It is around 20 megabytes in size. One can place between 100 - 150 images (PAC) on a MASTER Photo CD. Software is available on computers that can convert these formats to a compatible graphic standard (ie GIF, TIFF, TARGA, etc). The five picture formats that are included in each image PAC are as follows: Image Resolution ========================== Base/16 = 128 x 192 pixels Base/4 = 256 x 384 pixels Base = 512 x 768 pixels 4Base = 1024 x 1536 pixels 16Base = 2048 x 3072 pixels In image PAC is a compressed form that includes all 5 resolutions of a single image and ranges from 4 to 6 megabytes on average. When used in a program, the image is decompressed so that it can be displayed. Stand-alone Photo CD players will play both standard audio CDs and display Photo CD images on the television screen. Anyone will be able to enlarge and manipulate the Photo CD images on a television to create custom Photo CD albums with the players. Kodak's Photo CD players and Philips CD-I players both work quite nicely. For use with a CD-ROM on a computer system one needs to have the following: * CD-ROM/XA (mode 2 from 1 sectors) and CD-BRIDGE format compatibility * Display system (24-bit color is recommended for best results) * Software driver that can read/access Photo CD discs. In the future, Kodak Photo CD logos will be placed on compatible drives. How is a photograph placed on a Photo CD? * KODAK PCD Film Scanner digitizes 35-mm negatives or slides. The film is scanned at a minimum resolution of 2048 x 3072. The three RGB values (primary colors Red, Green, and Blue) are given 12-bits each for color values. * Image data is encoded and color adjustments are performed in addition to compression. This is all done to achieve consistent, high quality prints. The image color is reduced to 24-bits. * The digitized image is then written to a Photo CD disc. It is written to disc via CD-Writer device. / A Graphical view of the Kodak Photo CD Finishing Process / PCD = Photo CD [ EXPOSED FILM ] | | [ FILM PROCESS ] → [ PRINTER/PAPER PROCESS ] | | | | [Negatives (or Slides)] [ CONSUMER PRINTS] | | [KODAK PCD Film Scanner] | | [KODAK PCD Data Manager (computer)] → [KODAK PCD Printer] | | | | [KODAK PCD WRITER ] [KODAK Index Print] | | | [ Kodak Photo CD disc ] | |——-|————————————| | | | | | | Home TV Viewing Personal Compututing | | | | [Kodak Photo CD Player] [CD-ROM (XA, Multi-Session) ] One can find out more information on Photo CD by contacting the Kodak Information Center (KIC). –==– J) What is multi-session and why is it important to Photo CD? Multi-Session is the ability to read more than one table of contents. One can think of a book when thinking of table of contents. A single session drive can only read one session. This is similar to a 10 chapter book and only being able to read the first chapter. With multi-session, one can read all sessions that were written at different times. If this were a book you would be able to read all 10 chapters. The advantage of multi-session is being able to place photographs taken at different times. For example if one takes pictures during summer vacation they can be placed on a Photo CD disc. At Christmas time you take more pictures and they can be added to the disc as well. Every time one adds a new set of pictures to a disc it is called a session. So one can see what a useful feature Multi-Session capability is. NOTE: Multi-Session works with all forms of CD-ROM data including Kodak's Photo CD. So having multi-session one is not limited to the types of data that can be added to the disc later on. –==– K) Interview with Scott Brownstein - Manager Advanced Projects at Kodak (summary of the interview) AD = Albert Dayes SB = Scott Brownstein AD: How long was the development process for Photo CD? SB: Approximately 5 years. AD: Ending in January 1992? SB: Yes AD: What computer was used for the development of Photo CD? SB: Many different types ranging from MACs to VAX clusters to Sun SPARCstations, etc. AD: There are currently only 5 formats for Photo CD including Master, PRO, Catalog, Medical and Portfolio. NOTE: a general overview of the different formats was not part of the interview. MASTER format has a pac format with 5 different resolutions and can store about 100 to 150 images. PRO format which has higher resolution and supports larger film formats other than 35-mm. These include 70mm, 120mm and 4 x 5 inch, etc. CATALOG format has low resolution than base images and can contain up to 6000 images. MEDICAL format is for storing CT (Computed Tomography) and MRI (Magnetic Resonance Imaging) pictures in addition to standard film formats. It can also be used for other diagnostic scans like Ultrasound, PET (Positron Emission Tomographic) and Angiogram. PORTFOLIO format allows the mixing of images, text and audio and branching capability, all on one disc. These images are base resolution. END NOTE: AD: How does the Catalog format work? SB: It contains about 800 video pages and each page can have multiple images on it. Each image has an index and can be used to present a presentation. Using indexes and branching one can generate a unique presentation. Using Kodak's Shoebox software you can find any image by using a keyword search. The Shoebox software works with smaller storage requirements all the way up to very large jukeboxes with a capability of over 100 Photo CD discs on-line at one time. AD: And the Portfolio? SB: It allows for the mixing of text, audio and images and Kodak will have authoring tools out in 1993. The audio in this case can be either CD audio (Red Book) or ADPCM. The branching is just an access method and in this case interactive programmed access. AD: What makes the PRO format different from the MASTER format? SB: The PRO format can use film sizes larger than 35-mm and allows for a max resolution of 8,000 x 12,000. It also has data encryption and security features. For example watermarking. Each image can be given its own unique key to effectively lock the image. The watermark allows for the picture to display but have a message across it like "PROOF" or "COPYRIGHT 1992", etc. So without knowing the key this watermark will always be displayed on top of the image. Once the person uses the correct key then the watermark will be removed from the image being displayed. AD: Are images scanned at 24-bit resolution? SB: No, they are scanned at 12-bits per RGB (Red, Green and Blue values). The software then compresses it to 24-bits. The 24-bits is actually made up of 8-bits for luminance and the rest for chroma. AD: What is Kodak's Picture Exchange? SB: Basically it allows people to store images on a consignment basis. The fees are based on storage, referral and cross platform. AD: How does one access Kodak's Picture Exchange? SB: Anything with 9.6 (9600 baud) and higher can have access. AD: What has been the response to Photo CD? SB: It has been extremely positive. Having cross platform capability and ISO-9660 helps quite a bit. In addition it reaches both the low and the high end with the same technology. Also with Kodak providing automatic scanning equipment speeds up the process of translating film to Photo CD discs. AD: What about multi-session? Are all of Kodak's Photo CD players multi-session? SB: Yes all Kodak's Photo CD players are multi-session and so are CD-I players. The newer CD-ROM drives are also getting that capability as well. In addition they can all play regular audio CDs. AD: What about CD-WO and multi-session? SB: This entire area of CD technology is very exciting. So instead of being stuck with a 100 megabyte CD you can now add to it. One can add any type of data because of multi-session technology. Since there is no blank spaces between the data after the drive reads it, it will think that it has just a larger CD-ROM. Normal CD-audio will not work since it is not part of the specification. It is a problem with audio CDs needing TOCs. But if the audio is recorded in the first session it will be fine. The advantage of this technology is 1) it is WRITABLE and 2) it is PRESSABLE. Consider the low cost of floppy disks but then think of long it takes to write data to one. Once you have a CD you can just have them pressed. The average time to press a CD is about 4 to 6 seconds or approximately 100 megabytes per second. It makes perfect distribution and duplication sense. With a recordable CD it is almost the same as having a 600 megabyte floppy. AD: What is the most important aspect of Kodak Photo CD technology? SB: Actually there are three things: a) cross platform b) digital audio and digital video c) high end (PRO market) and low end (Consumer market) AD: Thank you –==– L) Which is the best CD-ROM drive to buy? First thing it must be a SCSI CD-ROM drive! If you just want to read data disks you can buy one of the older generation drives. Make sure that the maker of the driver software has tested your drive so you will not be stuck when it doesn't work. In this case contact ICD or Atari. Also if you need Photo CD compatibility you need one that is both multi-session and CD-ROM/XA compatible. Most of these new drives are either just becoming available or will be coming out in early 1993. Price range is under $800. The drivers for regular CD-ROMs are available from Atari and ICD. One should contact either of the two companies for additional information. At COMDEX, in the Atari Booth the CD-ROM drive being used for Photo CD was a Toshiba TXM3301B1. This is a single-session model and software at the time was only single session. Currently the software only supports MULTI-SESSION on the TT030 and Atari Falcon030, and only SINGLE session on the ST. It is a possibility that multi-session capability will work on the ST in the future. Michael Bernards wrote the driver software for Photo CD on the Atari and Calamus SL (DTP) Photo CD access software. Calamus SL has an Photo CD importer that supports all five resolutions of an image. One should contact the references given below for additional information on availability of the Photo CD drivers. Kodak certifies CD-ROM drives that are compatible with Photo CD as well. The best method is to ask on an on-line service and consult magazines or call the Kodak Information Center. Also consult with the maker of driver software since they usually have a compatibility list of drives they have tested as well. Toshiba, Pioneer, Sony and other have stated they will have CD-ROM drives that will support CD-ROM/XA, multi-session and Photo CD. The current CD-ROM/XA, multi-session Photo CD compatible drive from Toshiba is TXM3301E1. This one is the only one currently shipping. Upgrades from earlier versions of the TXM3301 are possible (depending on serial number) contact Toshiba for more information. The year 1993 is not only the year of the Atari Falcon030 but the year of the CD-ROM/XA multi-session CD-ROM drives. Many will be coming out all during the 1993 year and prices are dropping! RECOMMENDATION: Buy a CD-ROM/XA multi-session SCSI drive. The cost is not that much higher than normal SCSI drives and you will be able to enjoy a long future with Photo CD and CD-ROM. Summary: For general use: 1) SCSI CD-ROM drive (external)* 2) SCSI host adapter (TT030 and Atari Falcon030 have built in SCSI ports. The ST family requires SCSI host adapters like ICD). 3) SCSI driver software that supports CD-ROM drives. 4) SCSI cables and power cables as needed.

For multi-session, and Photo CD support:

1) SCSI CD-ROM/XA, multi-session and Photo CD (external)* 2) SCSI host adapter (TT030 and Atari Falcon030 have built in SCSI ports.

                   The ST family requires SCSI host adapters like
                   ICD). ****

3) SCSI driver software that supports CD-ROM drives. 4) SCSI driver software for Photo CD support.* 5) SCSI cables and power cables as needed.

* Internal drives are possible but require additional work. Contact your

dealer for more information.

Be sure your CD-ROM drive has been tested with CD-ROM driver software before purchasing one. * Be sure your CD-ROM drive has been tested with both the CD-ROM driver

  software and Photo CD software before purchasing one.

The Photo CD software driver for the ST is currently single session


/*/ CONTACTS for ATARI related CD-ROM and PHOTO CD products.

Atari Corporation 1196 Borregas Ave. P.O.Box 61657 Sunnyvale, CA 94088 USA (408) 745-2000

They also can be contacted on GEnie.

Products: MetaDOS, CD-ROM drivers, Photo CD drivers, Developer information, Photo CD developers' kit

Beckemeyer Development Tools P.O.Box 21575 Oakland, CA 94620 (510) 530-9637 (510) 530-0451 (fax)

Products: Hard disk backup, optimization software, SCSI Tape backup software

ICD 1220 Rock Street Rockford, IL 61101-1437 USA (800) 373-7700 (orders) (815) 968-2228 (815) 968-6888 fax

COMPUSERVE: Atari Vendors forum (GO ATARIVEN) GENIE: ICD RoundTable

Products: SCSI Host Adapters, SCSI Driver Software and CD-ROM driver software

DMC PUBLISHING 2800 John Street, Suite 10 Markham, Ontario L3R 0E2 CANADA (416) 479-1880 (416) 479-1882 (fax) (was ISD Marketing at one time)


Products: Photo CD importer for Calamus SL (DTP) supporting all 5 resolutions.

Oregon Research Associates 16200 S.W. Pacific Highway, Suite 162 Tigard, OR 97224 (503) 620-4919 (503) 639-6182 (fax)


Products: Hard disk backup and optimization software, SCSI Tape backup software

/*/ ISO-9660 filesystem made EASY

This is a very simple filesystem and it very easy to understand. The first thing that happens it sector #16 is read. It then checks for the primary volume descriptor.


1-2-3-4-5-6-7-8-9-10-11-12-13-14-15- |16| ←———

  1. — |



Check sector 16 for a Primary Volume Descriptor ——

If Sector 16 contains the Primary Volume Descriptor then jump to the root directory. The root directory is given as an absolute sector number within the primary volume descriptor.


 ID = "CD001";
 other information;
 location of root directory on the disc; ----
 size of root directory;                    |
 other information;                         |
}                                           |

ROOT DIRECTORY ←——————————

The root directory contains the list of files and sub-directories. All files and directories on an ISO-9660 CD-ROM are called directory records.

Here is an example of a root directory:

file_1.txt;1 ←—- file file_2.doc;3 ←———— file sub_dir.;2 ←—- sub directory

If we want to examine file_1.txt;1 and we read the directory record. The directory record indicates what sector (absolute) that the file starts on and how long the file is in bytes.


 other information;
 location of file on the disc;-----------------
 size of the file (in bytes or characters);   |
}                                             |

data for the file ←—————————–

Now suppose we want to go to the sub-directory named sub_dir.;2


 other information;
 location of sub directory on the disc;-----------------
 size of the sub directory (in bytes or characters);   |
}                                                      |

data for sub directory ←———————————

The data for this sub-directory is different than the file. The data is a list of all the files and sub directories in the directory. The size of this sub-directory is given by its length in bytes.

An example of the data in the sub-directory;

. ←— current sub-directory .. ←— parent directory of this sub-directory named sub_dir.;2 file_99.doc;1

To read the file_99.doc;1 one uses the same method out-lined earlier to get to file_1.txt;1.

The question is now how do we get back to the parent directory? We read the ".." directory record. Then jump to the location (absolute) sector of the current directory's parent which in this case is the root directory.


 other information;
 location of parent directory; ----|
 size of parent directory;         |
}                                  |

parent directory data ←————–

The parent directory is read and its contents displayed. In this case the parent directory is the root directory.

file_1.txt;1 ←—- file file_2.doc;3 ←———— file sub_dir.;2 ←—- sub directory

We are back to where we started again. It is not very hard to follow it at all. It very similar to the filesystem in our Atari and IBM PC computers, you might have noticed.

The filenames and sub-directory names look strange. Basically the filenames are the same type as on the Atari. Its 8.3 format (for example ATARI456.DOC) is very familiar. There is some extra characters on the end and they add a version number. For example on some computers like Digital's VAX every time you save the file the version number is updated.

For Example:


save the file again

file.dat;2 ←—- version number is updated after the file is saved.

Other than a few small things, ISO-9660 and the Atari filesystem are very similar. As one can see the ISO-9660 CD-ROM filesystem is even simpler than the normal Atari filesystems. For more technical details on the ISO-9660 standard one needs to buy the ISO-9660 specification since it is copyrighted by ISO.


When the CD-ROM drive first spins up it checks for the presence of a TOC (table of contents) on the CD. This gives information about how big the disc is in general terms. The first TOC is always in the same location so all CD-ROM drives and Audio CD players check for its presence everytime they are turned on.

With Multi-Session the entire disc has to be checked to see if more than one session exists. The disc has a beginning and ending for each session on the disc. So on a multi-session disc there will be several TOCs and beginning and ending sections one for each session. The beginning and ending sections are usually referred to lead in and lead out.

LI = (lead in) beginning LO = (lead out) end TOC = Table Of Contents (which is actually part of the lead in section)


SINGLE session disc:



MULTI-session disc:





Who says CD-ROM/XA multi-session drives tell the truth?

The CD-ROM/XA multi-session drive looks at a disc and reads the first Table Of Contents. The software driver asks if the CD-ROM/XA multi-session drive has found the end yet. The CD-ROM drive lies and says no and continues searching until it finds the last TOC on the disc. The CD-ROM/XA multi-session drive replies with a YES when has found the last session on the disc.

The best part about a multi-session is that one can add data at any time whenever one needs to. It will be a great way to make updates to the family album using a Photo CD disc as one's album. So many possibilities and all available on the Atari too.

// Making My OWN CD-ROM made EASY

Walnut Creek provides a service to make a master CD-ROM for only $200. They will take 600 megabytes on TAPE or floppies. Yes floppies disks are accepted provided they are in MS-DOS format. Strange thing is Atari format is the same as MS-DOS format. Does that give any one any ideas? <HINT, HINT>

And with a Multi-Session CD-ROM/XA drive you can always add more data later on to the disc.

// An Atari Dream CD-ROM

A dream CD-ROM for me would be to have all the articles in STart, ST-LOG, ST-Applications, and Antic all on one CD-ROM. Just think all of those articles and program listings in the palm of your hand.

It is not very fun searching through many STart magazines looking for that great David Small article on the floppy disc controller (STart magazine Fall 1987, I think?). All those great programming articles in one place… WOW! A CD-ROM would be perfect.

Just think of being able to look up all past reviews from all the different magazines in one place. A hint … CD-ROM would be nice! Trying to remember which magazine which they built a hard drive in… you could search for it in seconds on a CD-ROM. Just think - complete text files and Degas pictures for the diagrams too.

Remember something David Small said at one of his shows? "I want my MAC-ST!" How about a new one.



ADPCM = Adaptive Differential Pulse Code Modulation (audio that

            allows compression) and is used in CD-ROM/XA.

AES = Audio Engineering Society AIIM = Association for Information and Image Management ANSI = American National Standards Institute

            (sets industrial standards for the USA)

ATARI = Manufacturer of the World's Greatest Computers! CD = CD or CD-DA is digital audio CD that we all enjoy listening

            to. (RED BOOK) CD stands for Compact Disc. Stereo 16-bit
            sound sampled at 44.1KHz.

CD-BRIDGE = Is an extension to CD-ROM/XA and is what Photo CD uses.

            This allows for Photo CD discs to be played on CD-I
            players as well. It adds additional information at the
            track level of CD-ROM/XA track.

CD-I = CD-Interactive similar to CD-ROM and supports sound,

            full motion video as well as data introduced by
            Philips Corp. (GREEN BOOK)

CD-ROM = Based on audio CDs and is a read only medium and holds about

            680 megabytes of information. (YELLOW BOOK)

CD-ROM/XA = CD-ROM eXtended Architecture is needed for Photo CDs. Special

            information is added at the track level to give additional
            features. This is a joint Philips, Sony and Microsoft
            specification that deals with interleaving audio with data.

CD-R = A recordable CD. See CD-WO. CD-WO = The disc can be written to many times but not erased. Tracks

            are on the disc but data is not present. Data can be added
            later on. (ORANGE BOOK part 2)

CHROMA = Color attributes, such as shade, saturation and hue. CLIENT = In very general terms a "front end". Receives services

            from the server. See server.

DISC IMAGE = An exact represent of bits that will be put on the CD-ROM.

            This should not be confused with a graphic "image."

DRIVER = A series of instructions that is used to reformat the data

            from a particular peripheral device to something the
            computer can use. A printer driver is a good example.

EDC/ECC = Error Detection Code and Error Correction Code. GREEN BOOK = The document which describes both disc format and

            hardware specifications for Philips' proprietary CD-I

HIGH SIERRA = (HS) the 1986 CD-ROM standard was superceeded by ISO-9660. ISDN = Integrated Services Digital Network - basically allows for

            voice, data and video to be used at the same time. This
            could be said to be a vehicle for a single service that
            supports all forms of signal traffic on a single platform.

ISO = International Organization for Standardization

            (70+ standard organizations in different countries are

ISO-9660 = This international standard specifies the filesystem on

            CD-ROM discs. (ISO 9660, 1988)

LUMINANCE = Portions of composite video signal that control brightness. MASTERING = The process of physically making a disc. The facility is

            very similar to the clean room used in making computer
            chips. A glass master is "cut" using a laser; one or more
            negative nickel stampers are made; and those are used to
            produce the many copies of the CD-ROM.

MO = Magnetic Optical drive is read/write (many times)

            optical device. Also defined in the ORANGE book part I.

MULTI-SESSION = The ability to read more than one session on a disc.

              Very important for Photo CD. (Orange Book Part 2)

NISO = National Information Standards Organization. ORANGE BOOK = Describes Magnetic Optical Disks and CD-Write Once discs.

            It also deals with Multi-Session as well.

PREMASTERING = The method to produce a CD-ROM before sending it to a

             mastering facility. This usually includes making the
             ISO-9660 filesystem, adding error checking and correcting
             code and making an image and then transferring the disc
             image to tape.

PHOTO CD = Kodak's standard for storing pictures on CD-ROM discs. POSIX = Formal description of one form of operating system of which

            UNIX is an example. Many parts of UNIX are POSIX compatible
            but not all of UNIX. POSIX specifics specific functions
            that are part of the standard.

RED BOOK = CD audio standard introduced by Philips and Sony ROCK RIDGE = Based on the fictional town in the movie "Blazing Saddles"

            is an extension to ISO-9660 that allows for all the
            special features in the UNIX filesystem to be used. Discs
            formatted with Rock Ridge extensions can still be read
            with any ISO-9660 driver.

SCSI = Small Computer System Interface (ANSI X3.31, 1986) allows

            up to 7 devices (printers, hard disks, scanners, optical
            drives, CD-ROM drives, networking cards and more) to a single
            interface card.

SERVER = In very general terms… "back end" (provides services to

            a client). Usually thought of in a client-server type of
            relationship. File server, printer server are good examples.

SGML = Standard Generalized Markup Language - provides a system

            for tagging text structures with generic identifiers
            which mark the category or class to which a piece of
            text belongs. (ISO 8879, 1986)

SINGLE SESSION = The ability to read one TOC (table of contents) or one

               session. All CD-ROM drives generally fall into this
               category. Usually made in reference to Photo CD.

TOC = Table of Contents (similar to the table of contents found

            in a book). All CDs have one or more of them. This also
            gives information on where the tracks start.

UNIX = An operating system created by AT&T Bell Laboratories in 1971.

            It has become a very popular operating system and it runs on
            many different platforms. Unix International (UI) and
            USL (Unix System Laboratories) are in charge of promoting
            and enhancing the UNIX standard.

WORM = Write Once Read Many device. You can only write to one

            area on the disc once but you can read it many, many times.
            The data that has been written can never be overwritten.

YELLOW BOOK = CD-ROM standard like the red book also by Sony and Philips.

// CD-ROM Drive manufacturers (not a complete list)

Chinon America, Inc 615 Hawaii Avenue Torrance, CA 90503 USA (800)-441-0222 (310)-533-0274

Hitachi Home Electronics 401 West Artesia Blvd Compton, CA 90220 USA (800)-369-0422 (310)-537-3766

NEC Technologies 1255 Michael Drive Wood Dale, IL 60191 USA (800)-366-0476 (800)-FONE-NEC (708)-860-9500

Panasonic Communications Two Panasonic Way Secaucus, NJ 07904 USA (800)-742-8086 (201)-348-7000

Philips Consumer Electronics 1 Philips Drive Knoxville, TN 37914 USA (615) 475-8869

Pioneer Communications of America 600 E. Cresent Ave Upper Saddle River, NJ 07458 USA (800)-527-3766 (201)-348-7000

Sony Corp of America 655 River Oaks Pkwy San Jose, CA 95134 USA (800)-352-7669 (408)-432-0190 (408) 434-6644

Texel 1605 Wyatt Drive Santa Clara, CA 95054 USA (800)-886-3935 (408)-980-1838

Toshiba America Information Systems 9740 Irvine Blvd Irvine CA 92718 USA (800)-456-DISK (714) 455-0407 (714)-538-3000 (714) 583-3129 (upgrade info)

/*/ Sources for the standards and general information:

Audio Engineering Society (AES) 60 East 42nd Street New York, NY 10165-2520 USA

Association for Information and Image Management (AIIM) 1100 Wayne Avenue, Suite 1100 Silver Spring, MD 20910 USA (301)-587-8202

A professional association dedicated to document and information automation and imaging. Includes applications of micrographics, optical, and computer technology and systems for the information professional.

American CD-I Association 11111 Santa Monica, Suite 750 Los Angeles, CA 90025 USA (213)-444-6619

Green Book or CD-I information

American National Standards Institute 11 West 42nd Street New York, NY 10036 USA 212-642-4900

ANSI specifications

CD-ROM Professional Magazine 462 Danbury Road Wilton, CT 06897 (800)-248-8466

This is a very good magazine for anyone in the CD-ROM business.

COMPUSERVE 5000 Arlington Centre Blvd Columbus, Ohio, 43220 USA (800)-848-8990 (614)-457-8650


file(s): SCSI specifications I and II (working specifications and not the

       official which are only available from ANSI, ISO or Global
       Engineering Documents).

CD-ROM forum: (GO CD-ROM)

file(s): Complete Rock Ridge specification, High Sierra specification,

       CD-ROMF.ZIP, CDFAQ.TXT (frequently asked questions about CD-ROM),
       and many other files.  The other files deal with steps necessary
       to make your own CD-ROMs, retrieval engines, CD-ROM related
       periodicals, vendors (that sell CD-ROM discs), manufacturers
       and CD-ROM consultants.


file(s): The C source for the December 1992 issue which has an article on

       the ISO-9660 CD-ROM filesystem.


section (5): Dedicated to Kodak's Photo CD

Dr. Dobb's Journal 411 Borel Ave San Mateo, CA 94402 USA (800)-688-3987 (415)-358-9500

A magazine dedicated to programming. The December 1992 issue had an article called "INSIDE THE ISO-9660 FILESYSTEM FORMAT." Future articles will cover Rock Ridge, CD-I, and CD-ROM/XA.

Eastman Kodak Company Information Center 343 State Street Rochester, NY 14650 USA (800)-242-2424 ext. 53 - for information of Kodak Photo CD products

                       and compatible CD-ROM drives
             ext. 36 - Locations to get Photo CD discs made

Kodak services, imaging, Photo CD, Photo CD compatibility information

GLOBAL ENGINEERING DOCUMENTS: 2805 McGraw Ave Irvine, CA 92714 USA (800)-854-7179 (714)-261-1455 (714)-261-7892 (fax)

More than a million documents. ISO specs and index, ANSI specs and index, Engineering specs, Government standards, Software Standards and much, much more. What don't they have?

Interactive Multimedia Association 3 Church Circle, Suite 800 Annapolis MD 21401-1933 USA (410)-626-1380 (410)-263-0590 (fax)

High level membership actively working on technical standards for cross-platform compatibility of authoring and delivery systems.

National Information Standards Organization (NISO) PO Box 1056 Bethesda, MD 20827 USA (301) 975-2814

A volunteer organization which develops ideas for a standard and then passes it to standard organization like ANSI and ISO.

Optical Publishing Association PO BOX 21268 Columbus, OH, 43221 USA (614)-422-8805 (614)-442-8815 (fax)

OPA is the Optical Publishing Association, a non-profit trade and professional group directed at helping publishers and all other players build a digital publishing market. They also publish materials, including a newsletter "Digital Publishing Business," and one can contact via COMPUSERVE Rich Bowers of the OPA ( CIS id = [71333,1114] ) for more information.

Prentice Hall Englewood Cliffs, NJ 07632 USA

BOOK: SCSI: Understanding the Small Computer System Interface

     by John Lohmeyer (Standards Architect, NCR Corporation)
     Chairman X3T9.2 (scsi committee)
     Discussion of SCSI-1, and a little on SCSI-2 and SCSI-3.

SCSI BBS ( operated by NCR corp ) USA (719)-574-0424 (bbs)

Source for SCSI information and working specifications not the complete specifications which must be bought from ANSI or GLOBAL ENGINEERING. This includes SCSI-1, SCSI-2, and Fast SCSI, Wide SCSI and SCSI-3.

Tech Specialist 2601 Iowa Lawrence, KS 66046 USA (913)-841-1631

The May 1991 of Tech Specialist had several articles on CD-ROM. a) "The ISO 9660 File System: A Reference Document" b) "Designing A CD-ROM Retrieval System" c) "Networking A CD-ROM drive"

Tech Specialist is published by R&D Publications which also publishes the C USERS JOURNAL.

Walnut Creek CD-ROM 1547 Palos Verdes Mall, Suite 260 Walnut Creek, CA 94596 USA (800)-786-9907 (510)-947-5996 (510)-947-1644

Pre-Mastering and Mastering Services, also sells usenet/internet archives on CD-ROM. They will make you a master CD-ROM for $200 and up. Both ISO-9660 and Rock Ridge formatting are supported.

CD-ROMs (CICA, Simtel20, Source Code, X11r5/GNU, C User's Group CD-ROM, etc.)

Microsoft MS-DOS CD-ROM Extensions 2.1

The format of the directory record for High Sierra discs is:

   /* High Sierra directory entry structure */

typedef struct hsg_dir_entry {

  uchar      len_dr;        /* length of this directory entry  */
  uchar      XAR_len;       /* length of XAR in LBN's          */
  ulong      loc_extentI;   /* LBN of data Intel format        */
  ulong      loc_extentM;   /* LBN of data Molorola format     */
  ulong      data_lenI;     /* length of file Intel format     */
  ulong      data_lenM;     /* length of file Motorola format  */
  uchar      record_time[6];/* date and time                   */
  uchar      file_flags_hsg;/* 8 flags                         */
  uchar      reserved;      /* reserved field                  */
  uchar      il_size;       /* interleave size                 */
  uchar      il_skip;       /* interleave skip factor          */
  ushort     VSSNI;         /* volume set sequence num Intel   */
  ushort     VSSNM;         /* volume set sequence num Motorola*/
  uchar      len_fi;        /* length of name                  */
  uchar      file_id[...];  /* variable length name upto 32 chars       */
  uchar      padding;       /* optional padding if file_id is odd length*/
  uchar      sys_data[...]  /* variable length system data              */
  } hsg_dir_entry;

The format of the directory record for ISO-9660 discs is:

   /* ISO-9660 directory entry structure */

typedef struct iso_dir_entry {

  uchar      len_dr;        /* length of this directory entry  */
  uchar      XAR_len;       /* length of XAR in LBN's          */
  ulong      loc_extentI;   /* LBN of data Intel format        */
  ulong      loc_extentM;   /* LBN of data Molorola format     */
  ulong      data_lenI;     /* length of file Intel format     */
  ulong      data_lenM;     /* length of file Motorola format  */
  uchar      record_time[7];/* date and time                   */
  uchar      file_flags_iso;/* 8 flags                         */
  uchar      il_size;       /* interleave size                 */
  uchar      il_skip;       /* interleave skip factor          */
  ushort     VSSNI;         /* volume set sequence num Intel   */
  ushort     VSSNM;         /* volume set sequence num Motorola*/
  uchar      len_fi;        /* length of name                  */
  uchar      file_id[...];  /* variable length name upto 32 chars       */
  uchar      padding;       /* optional padding if file_id is odd length*/
  uchar      sys_data[...]  /* variable length system data              */
  } iso_dir_entry;

The difference between the two forms is the file flag byte moved to account for an additional byte of date and time used for a Greenwich mean time offset. See the May 28th draft of the High Sierra proposal or ISO-9660 for a more complete explanation of the fields. Note that the C structs above are not syntactically correct; C does not allow variable length arrays as struct elements.

Choice of Filename Characters

On the first Microsoft Test CD-ROM disc, the Codeview demo failed because certain filename characters that were legal on MS-DOS were not allowed according to the High Sierra file format. When the software looked for file 'S1.@@@', it wasn't found because the character '@' is illegal for High Sierra filenames and during High Sierra premastering, the file was renamed 'S1'.

Valid High Sierra filename characters are the letters 'A' through 'Z', the digits '0' through '9', and the underscore character '_'. All other characters are invalid. Note that the letters 'a' through 'z' are not included so that High Sierra file names are not case sensitive. Under DOS, filenames are mapped to upper case before they are looked up so this is typically not a problem. When choosing file name characters, keep in mind the restrictions of the file structure format and the operating systems your media may be targeted towards.

Depth of Path

The High Sierra format allows for pathnames to be up to 8 levels deep. It's possible to create a path on MS-DOS that is deeper than that but you won't be able to transfer it to a CD-ROM.

\one\two\three\four\five\six\seven\eight\file.txt /* Ok */
\one\two\three\four\five\six\seven\eight\nine\file.txt /* Illegal */

Length of Path

The High Sierra format allows for the entire pathname to be a maximum of 255 characters. Since MS-DOS imposes a limit far lower than this, this should not present a problem. The MS-DOS call to connect to a sub-directory is limited to a directory string of 64 characters. The length of path restriction is more a concern for Xenix/Unix than MS-DOS.

Amusingly enough, the MS-DOS call to create a sub-directory allows a directory string greater than 64 characters which allows you to create sub- directories that you cannot connect to.

Unfortunately, a CD-ROM may potentially contain a pathname that is much larger than 64 characters long. This is not a concern here but is discussed in a related memo - "MS-DOSifying your CD-ROM". As a rule, try to keep the length of your longest path less than 64 characters and you should be pretty safe.

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