Path: utzoo!mnetor!uunet!portal!cup.portal.com!raf
From: raf@cup.portal.com
Newsgroups: comp.os.cpm
Subject: Re: CP/M directory extents
Message-ID: <4020@cup.portal.com>
Date: 22 Mar 88 05:31:45 GMT
References: <8803131014.AA03487@rand-unix.rand.org> <8803142001.AA02595@newton.arpa>
Organization: The Portal System (TM)
Lines: 25
XPortal-User-Id: 1.1001.2659


Bridger Mitchell <bridger%rcc@RAND-UNIX.ARPA> writes:

> Yes, directory calculations are confusing, and not helped by confusing
> terminology!

I agree, and I apologize for contributing to the confusion by use of
misleading terminology and (as I now realize) some innacuracy in my
previous posting.  In particular, my statement was *incorrect*, that
RC = 80h implies a full "extent" (meaning PHYSICAL extent, or directory
entry).

> The key point is to keep physical and logical extents distinct.

Yes, that certainly is the key to understanding CP/M directory entries.
Thank you for the clear explanation, Bridger.

[I think my mind was in the same place as those designers who failed
apparently to distinguish logical and physical extents, by not using
all 16 bytes of the allocation group number area.  Several years ago,
I puzzled over the DPB extent mask in a system (Zenith Z-100?) which I
believe falls into this category.  Only now, after reading your note,
do I understand that particular diskette format!]

Bob Freed                         Uucp:  ...!sun!portal!Robert_A_Freed
                              Internet:  Robert_A_Freed@cup.portal.com