Path: news1.icaen!news.uiowa.edu!news1.chicago.iagnet.net!iagnet.net!howland.erols.net!newsfeed.internetmci.com!193.174.75.126!news-was.dfn.de!news-fra1.dfn.de!news-ge.switch.ch!news-zh.switch.ch!elna.ethz.ch!not-for-mail From: GUDATH@EZINFO.VMSMAIL.ETHZ.CH (Henrik 'Ratte' Gudat) Newsgroups: comp.emulators.apple2 Subject: Re: Disk Image formats Date: 2 Dec 1997 07:25:20 GMT Organization: F.E.Systems Emulation Technologies Lines: 52 Distribution: world Message-ID: 660d50$8tj$1@elna.ethz.ch References: 19971201040901.XAA19285@ladder02.news.aol.com 34831774.6730572@news.bconnex.net NNTP-Posting-Host: ezinfo.ethz.ch X-News-Reader: VMS NEWS 1.24 In-Reply-To: CUTjefbla@bconnex.net's message of Mon, 01 Dec 1997 20:27:03 GMT
Hi guys,
2img is a public format, so here it is : 
Please note that subtype 2 (raw nibbles) has not been further discussed and is undefined as of this writing.
typedef struct {
char magic[4]; /* "2IMG" */ char creator[4]; /* Creator signature */ word16 header_len; /* Length of header in bytes k */ word16 version; /* Image version */ word32 image_format; /* Image data format (see below) */ word32 flags; /* Format flags (see below) */ word32 num_blocks; /* Number of 512-byte blocks in this image */ word32 data_offset; /* File offset to start of data */ word32 data_len; /* Length of data in bytes */ word32 cmnt_offset; /* File offset to start of comment */ word32 cmnt_len; /* Length of comment in bytes */ word32 creator_offset; /* File offset to start of creator data */ word32 creator_len; /* Length of creator data in bytes */ word32 spare[4]; /* Spare words (pads header to 64 bytes) */
} image_header;
Format numbers:
0 = DOS 3.3-order dump of disk data. This is really only valid for
a floppy disk image.
1 = ProDOS-order dump of the disk data. This is the only valid format
for a hard disk image.
2 = Raw dump of the disk nibbles. This is only valid for a floppy disk
image.
Flags:
0x80000000 = Image is write protected (1 = yes, 0 = no)
Now regarding .po and .do files: these files contain chunks of 256 bytes - the logical disk data. Important: the sectors (256 bytes) are arranged in DOS (.po) or ProDOS (.po) order. Both OSes have a very specific sector interleaf. This means, the disk images contain the sectors in the order as they appear under the drive head. So, sector 0 ius the first one but sector 1 is likely to be anywhere but the following sector. The interleaf is different fro ProDOS and DOS and described in DOS/ProDOS books.
I hope this helps. You can mail me if it's not clear, or post here.
- henrik