Date   : Mon, 19 Dec 1988 07:55:00 GMT
From   : mcvax!unido!nixpbe!ugun21!josef@uunet.uu.net
Subject: Recovering Erased CP/M Files

In his note Paul Knight (PKNIGHT@pucc.UUCP) writes:
>The following message from Dave Goodman (dgee@cup.portal.com) was the
>most comprehensive reply, so I post it here by way of summarizing the
>contributions of everyone who responded.
 
>*Yes, erased cp/m files can be recovered *provided* the disk has not
>*been written to since the erasure took place.
>*
>*When a file is erased, there is no physical erasure of the disk space
>*used by the file.  All that happens is the directory entry(ies) for that
>*file are marked as erased, with an 0e5h (0xe5 [or E5H], if you prefer)
>*in the first (user) field of the directory entry.
>*
>*Of course, the disk space used by the file is now marked as free, so if
>*a subsequent write to the disk is done, the space will be reused and
>*the old file will probably be physically overwritten.

My question is:
How is free disk space managed?

Reason for this question:
Some time ago, I had some problems with a self-written program
that caused blocks to be souped-up without being registered in a
directory entry.
What I mean by that is that these blocks seem to be marked as "in use"
but not being actually in use.
At that time I felt the need for a UN*X-like fsck-program for
my system (SB180FX with Z-System).


               Josef Moellers

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