GENWiki

The following is an exerpt from a text file written/complied by one A.D. Longton of Rockville, MD. I have omitted the discussion of how to make a 1.44M disk from a 720K disk with a soldering iron since I don't want to be a party to furthering that practice. I did, however, find the remainder of the information quite interesting and have included it here. As You can see, it comes directly from the 'brain trust' at Big Blue and may tend to lend some measure of credibility to what I've been saying all along. The original file was dated 5/10/89, I'm not sure when the information spewed forth from Boca Raton. -[Steve]- ™

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                         3.5" DISKETTE FORMATS
                              Kevin Maier
                            IBM Corporation
                          Boca Raton, Florida
                    "Reprinted by permission of the
                IBM Personal Systems Technical Journal."
                         Page 42, issue 2, 1989

   "The  original recommendations about the proper formatting and use
   of  PS/2 diskettes have undergone revision.  This article explains
   why the recommendations have changed.

                          THE ORIGINAL CAUTION

   Personal  System/2 shipping cartons include a sheet of paper  that
   cautions  users not to format a 2.0 MB diskette to 720 KB, because
   the diskette becomes unusable and should be discarded.

   This  caution was issued because of the physical properties of 720
   KB  diskettes versus 1.44 MB diskettes.  The 720 KB format uses  a
   higher  write current, and the  1.44 MB format uses a lower  write
   current.   To  accommodate  the  higher write current,  the  oxide
   coating on a 1.0 MB (720 KB formatted) diskette is denser than the
   oxide coating on a 2.0 MB (1.44 MB formatted) diskette.

   When  you format a 2.0 MB diskette to 720 KB, you apply the higher
   write  current  to  the  less dense oxide coating.   The  hardware
   developers  originally felt that this meant the 720 KB  formatting
   pattern  is  written too  deeply  into the 2.0 MB  oxide  coating,
   causing intermittent data errors and unreliable use.  Furthermore,
   the developers felt that if you attempted to reformat the diskette
   to 1.44 MB, which uses the lower write current, the 1.44 MB format
   would  not  completely  write  over  the "deeper" 720  KB  format.
   Therefore  the developers' recommendation was to discard a 2.0  MB
   diskette that was formatted to 720 KB.

                        THE SUBSEQUENT FINDINGS
                           [aka a RETRACTION]

   Since  the time that this caution was issued, the developers  have
   performed  additional testing, and have concluded that there is no
   need to discard a 2.0 MB diskette that was formatted to 720 KB.

   It  is still true that a  2.0 MB diskette formated to 720 KB  will
   cause intermittent data errors.  However, the latest assessment is
   that  you will be able to reformat the diskette to 1.44 MB and use
   it reliably after that.

   The  same logic applies to a 1.0 MB diskette formatted to 1.44 MB.
   You cannot use it with the 1.44 MB format, but you can reformat it
   to 720 KB and use it reliably after that.

   Therefore,   the  current  recommendation  is:  If  you  format  a
   diskettte  to  the  wrong  capacity, do not discard  it;  instead,
   reformat it correctly and use it."

   With  all those feelings  and recomendations on those feelings  it
   makes  me wonder how much experimentation was actually being  done
   on  a  strictly scientific level.   Note that the one  mention  of
   formatting  1.0mb disks to 1.44 MB does not say that you will  get
   errors  if you use them.  What it does say is that if you reformat
   that  wrongly formatted disk, you can reliably use it at 720  KB.
   The  implication is that since there were errors with 2.0mb  disks
   formatted  to 720 KB "logic applies" that there will be errors  if
   the  reverse is done.  This is not necessarly the case, and we are
   not told why, we are just told.

   FYI, here are the specifications for the 720 KB, 1.44 MB, and 360k
   5.25"  disk  drives  as  listed  in the same issue on pages 43-44.
   Note the large similarity between 360k and 720 KB disks and 720 KB
   disks and 1.44 MB disks.

                   720 KB and 1.44 MB Diskette Drives

                                720 KB     1.44 MB     360 KB (5.25")
   Access time:
        Track-to-track            6 ms        6 ms       6 ms
        Head settle time         15 ms       15 ms      15 ms
        Motor start time        500 ms      500 ms     750 ms^

   Disk rotational speed:       300 rpm     300 rpm    300 rpm
        Maximum Latency         200 ms      200 ms     200 ms
   Formatted Characteristics:   720 KB     1.44 MB^    360 KB^
        Tracks (actual)          80          80         40   ^
        Tracks per inch         135 tpi     135 tpi     48   ^
        Sectors per track         9          18   ^      9
        Bytes per sector        512         512        512
        Bytes per track        4608        9216   ^   4608
        Data heads                2           2          2
        Sector interleave factor  1:1         1:1        1:1
        Sector skew factor        0           0          0
        Sectors per cluster       2           1   ^      2

   Transfer rate            250,000     500,000^   250,000
   (bits per second)

   (All ^'ed numbers are numbers that are different from the 720 KB
   format.)

           "...if they think you're technical, go crude. ....
       These days, though, you have to be pretty technical before
                   you can even aspire to crudeness."

1. -From William Gibson's short story

Johnny Mnemonic