Track Compression (PC) Finished

22 September 2001

Finished the first version of track compression on the PC. Any bugs will be weeded out in due course, but generally it seems to work. Even better, it compresses multiple reads of tracks into a few bytes (usually less than 100). Each track is read 3 times [later this was increased to 5 - Ed.] to avoid redump if a read fails - and that is quite common, especially due to non-use, dust, etc.

Checksums have been added on both the compressed and the uncompressed track data, and so far on a few test images they are good.

Time to port to Amiga.


Notable pieces of development since the last update are:

  • Ported the track compressor to the Amiga.
  • Fixed some bugs and compiler issues.
  • Optimised the Amiga version so reading now takes around 2 seconds per track, this was from a much higher value.

Unrelated to the above optimisation, we found while testing that if “white noise” (an empty track) was on a track it was extremely slow to compress the data on the Amiga. This slowdown was obviously unrecognisable on a PC. Therefore the track compression was improved to detect white noise during compression(!) and stop the compression if noise was found. This enhancement made the processing of white noise tracks from up to 2 minutes to about 2 seconds. The average track size is now 15 Kb compressed, from an uncompressed size of 87 Kb. That makes roughly a 2.4 Mb compressed image from a 14 Mb uncompressed one.

Now it is high time to add whole disk dumping and check a few complete images (currently only one selected track is images for test purposes). Then we are ready to image disks, so soon a first working disk imaging tool “CT” can be posted.