Checksums & Descriptors

23 March 2002

CCITT is a standards body that produced what used to be the “de-facto” CRC (Cyclic Redundancy Check) that is used to verify there were no errors in a given piece of data (and still is for certain environments). You can find CRCs pretty much anywhere you can find data, especially nowadays - ironically media storage is more reliable now. As the name suggests this is a 16-bit checksum that is cheap to do in hardware, and works well on data of only a few Kilobytes, e.g. Disk data blocks. Developers may have used a CRC solution over Commodore’s native parity based system because it was so much more reliable.

Support for this checksum has been added to the analyser and is used to verify errors on disks that used it. This is essentially PC and Atari ST disks (useful for verifying those multi format games) and was also recently found on the Firebird disk format.

Firebird disk format now supported as suggested above including the CCITT CRC. There is another variant of this format, used on Rainbird (Firebird/Microprose) titles that is also supported (that has parity based error checking). We don’t know who wrote it, but it is sure to be the same person and worked for all these companies (or it was licensed). Whoever it was, they were nice enough to use a decent CRC on the Firebird format instead of the crappy Amiga parity.

Games which are known to use these two disk formats:

• Firebird
  • Starglider 2 (only one track)
  • Virus
• Rainbird
  • Betrayal
  • Carrier Command
  • Interface
  • Midwinter
• Micropose
  • F19-Stealth Fighter

Obviously when more games that use these formats are dumped, they will be automatically supported and thus no work required to convert to the release format.