To:	physmsa AT cantua DOT canterbury DOT ac DOT nz
Cc:	opendos AT delorie DOT com
Subject:	Re: File systems
Message-ID:	<19980203.175224.8959.1.editor@juno.com>
References:	<199802032142 DOT KAA29974 AT cantua DOT canterbury DOT ac DOT nz>
From:	editor AT juno DOT com (Bruce Morgen)
Date:	Tue, 03 Feb 1998 17:53:03 EST

On Wed, 04 Feb 1998 10:42:49 +1300 physmsa AT cantua DOT canterbury DOT ac DOT nz (Mr M
S Aitchison) writes:
>
[snip]
>
>All FAT-like file systems are derived from the CP/M idea with the
>change that the list of sectors isn't stored in the directory entries.
>That change made sense at first glance, but wasn't really a good
>design, even but 1980 standards.  Good file system design was already
>available for small computers in the 1970's, for example: Data
>General's RDOS (much, much more efficient then DEC's equivalents, or
>FAT).
>
>The funny thing is that RDOS ran in 64Kb of RAM (in fact the O/S took
>about 20Kb), so it isn't some big, complicated arrangement.  At its
>heart, there were two design features that *should* have been
>introduced into DOS some time. One is that the directory, SYS.DR, had
>hash-encoding - if you knew the filename you could probably get the
>directory entry with one disk read. 

Interestingly enough, DRI 
implemented directory hashing 
in CP/M-80 v3.0, aka 
"CP/M Plus."  QDOS (and 
therefore early MS-DOS) was 
apparently modeled on 
CP/M-80 v2.2, the most popular 
microcomputer OS product by 
far at the time.

[snip]

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