In comp.sys.apple2 Toinet  wrote:
> My understanding is:
> - standard GCR encoded disk
> - 35 tracks / 16 sectors with a specific interleave
> - a block is a set of 4 sectors
> - a block is 1024 bytes long
> - block number 0 starts on track 3, sector 0
> - blocks 80 to 8F are reserved for cp/m (tracks 0 to 2)
> - two blocks reserved for the directory (blocks 0 and 1)
> - a deleted file entry holds $E5 at offset 0
> - there are no load address nor file length
> - file length can be determined by the number of blocks)
> 
> If I understand correctly, the rc byte (offset +F) holds the number of
> 128-byte records in a file. I would have thought it held the number of
> 1024-byte blocks. Am I wrong?

Source code for the CP/M disk reader in CiderPress:

 
http://ciderpress.cvs.sourceforge.net/viewvc/ciderpress/CiderPress/diskimg/CPM.cpp?revision=1.1.1.1&view=markup

We discovered that, on some Microsoft Softcard, disks, blocks 80-8f can be
used to hold data.

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