DiskCopy 4.2 format specification
File format for Apple disk copy 4.2 definition, wiki version based on 0.99 by Jonathan Gevaryahu AKA Lord Nightmare Much information comes from the CiderPress and MiniVmac source codes. More authoritave information comes from http://www.nulib.com/library/FTN.e00005.htm This is also used in DiskCopy 4.1. DiskCopy 6.3.3 uses a version with tags omitted. DART is a variant which adds compression.
|0x00||byte||Length of image name string ('Pascal name length')|
|0x01-0x3f||63 bytes||Image name, in ascii, padded with NULs|
|0x40-0x43||BE_UINT32||Data size in bytes (of block starting at 0x54)|
|0x44-0x47||BE_UINT32||Tag size in bytes (of block starting after end of Data block)|
|0x52-0x53||BE_UINT16||'0x01 0x00' ('Private Word') AKA Magic Number|
Specifics of each Section:
- Length of image name string ('Pascal name length')
Technically this is part of the 0x01-0x3f area, as pascal strings apparently store their length as their first byte. Effectively the address of the last non-NUL byte of the image name. bytes after the end address are ignored, and sometimes are used to hold extra information, or hold garbage (in the case of the 1.44mb system 6.0.8 startup disk, this is leftovers in memory from the System Additions disk, so the string ends up being System Startupns)
- Note: A special (bug) case happens when the disk name is "-not a Macintosh disk", which the name is set to when using dc42 on non-mac diskettes. In that case, the length is set one byte too high; this is probably a bug in dc42 that was just never fixed.
0x01-0x3f, 63 bytes
- Image name, in ascii, padded with NULs
This is the image name string. It is copied from the volume name of the disk or diskette being imaged.
- Data size in bytes (of block starting at 0x54)
This has one of 4 values on most diskettes: 00 06 40 00 (409600 bytes) for 400k GCR disks 00 0c 80 00 (819200 bytes) for 800k GCR disks 00 0b 40 00 (737280 bytes) for 720k MFM disks 00 16 80 00 (1474560 bytes) for 1440k MFM disks