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From: mjg@ecsvax.UUCP (Michael Gingell)
Newsgroups: net.micro.trs-80
Subject: Re: TRSDOS disk format
Message-ID: <331@ecsvax.UUCP>
Date: Wed, 28-Aug-85 09:01:11 EDT
Article-I.D.: ecsvax.331
Posted: Wed Aug 28 09:01:11 1985
Date-Received: Sat, 31-Aug-85 03:41:18 EDT
References: <323@harvard.ARPA>
Distribution: net
Organization: North Carolina Educational Computing Service
Lines: 28

> 
> 	Can someone please tell me why TRSDOS (at least on a Mod. III)
> insists on setting the DAM (Data Address Mark) to deleted data on all
> sector writes except the directory (=track 17 which is written correctly)?
> I spent many hours tracking down the (self-modifyong) code that does this
> while attempting to transfer data to another computer (which will not
> read deleted data...) and I'm really curious.
> 
> 						Dan Lanciani
> 						ddl@harvard


It appears to go back to TRSDOS on the original Model I and to apply
to just about all the TRS80 DOSs. All sectors of all tracks use the
data mark FB except for the directory track which uses an F8. SInce
the directory does not occur on the same track for different DOSs
and for 35 vs 40 vs 80 track and single sided vs double sided it
gives some measure of security of the directory which is the single
most important piece of information on the disk. And since the
TRS80 uses a Western Digital FDC rather than that well known
pain in the neck from Intel/NEC it is easy to read and write to
different data marks so why not?

If you want to transfer files from TRS80 disks to PC or CP/M disks
there is a well known product for doing this already. Just read the
pages of 80 Micro.

Mike Gingell  ..decvax!mcnc!ecsvax!mjg