Date   : Tue, 20 Dec 1988 20:18:41 GMT
From   : wilker@tcgould.tn.cornell.edu (Clarence W. Wilkerson Jr.)
Subject: Recovering Erased CP/M Files

If I understand your question correctly, you want to know if
there is any part of the directory structure or reserved area
of the disk that records which blocks are in use.
  There is no explicit list as in MSDOS or TRSDOS. However,
  the BDOS maintains a bitmap of allocation blocks that it
  obtains from the directory entries. One side effect is that
  under CP/M one can have files that are linked for a single
  allocation block, and different for later blocks. If you
  erase one of these linked files, you have the risk of having
  the BDOS bitmap showing the allocation blocks as being free,
  when they really are not. I don't know of cases where the blocks
  can be marked as used when they should be free. I assume that
  the bitmap is updated or recreated after a control-C and relogging
  the disk, but I'm not sure. When I've had disks that had linked
  files ( easy to do after unerasing ) I've played it safe and rebooted
  after erasing what I did not want.