Now, that we have a tool to patch sectors and fix links we can incrementally improve the archive, usually by copying a single sector from a donor disk to the damaged disk. After fixing about a dozen disks I started looking at disk 349, in which the file DISCOM32.COM was shorter than the number of sectors in the directory.

What was going on? According to the directory the file started at sector 13 and was 105 sectors long. The next file started at sector 118, so you'd expect this file would just be a continuous chain of sectors from 13 to 117. When I mapped it out, the linkage had a gap. 13-21, 37-117. After studying the sectors from 21-36 for awhile, they looked backwards, 36 should have been 21, 35 => 22, et cetera. Somehow most of track 1 (sectors 19-36) had been dumped out of order.

So patting myself on the back I made a copy of the disk and then patched the 16 sectors in the "correct order" onto the copy which gave me a file that was the right length, but still wasn't quite right. Even after reordering four of the sectors had file index numbers that didn't match the rest of the file. Sectors 19, 23, 56 and 84 were marked as from file 2 whereas the rest of the sectors were marked as file 1. Comparing the data with another copy of the file from D:\UMICH\ARCHIVER\DISKCOMM.ATR suggested those sectors were from a different file/disk altogether. So using sectors 89, 93, 126, 154 from the umich disk I was able to complete fixing the file.

So in the final summary, I needed to move 15 sectors and copy 4 sectors from another disk. This resulted in a file that matched other versions of the file, so it's highly likely it's a better match for the original disk contents, but you have to wonder how the disk got damaged like that in the first place.