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From: allbery@ncoast.UUCP (Brandon Allbery)
Newsgroups: comp.sys.ibm.pc
Subject: Re: SIMTEL20
Message-ID: <3274@ncoast.UUCP>
Date: Mon, 20-Jul-87 23:02:42 EDT
Article-I.D.: ncoast.3274
Posted: Mon Jul 20 23:02:42 1987
Date-Received: Sat, 25-Jul-87 10:41:42 EDT
References: <4UyCLWy00WAKI9k178@andrew.cmu.edu> <881@omepd>
Reply-To: allbery@ncoast.UUCP (Brandon Allbery)
Followup-To: comp.sys.ibm.pc
Organization: Cleveland Public Access UN*X, Cleveland, Oh
Lines: 34
Sigh. Nothing like rampant misinformation.
The TENEX ftp mode is misnamed; it should be called TOPS, or perhaps PDP-10.
The reason is that "TENEX" is not the basic operating system using that
particular mode; the problem is a hardware one, not a software one.
The basic problem is that the PDP-10 architecture uses 36-bit words rather
than 8-bit bytes. IMAGE mode for these machines transmits 36-bit words;
TEXT mode probably uses 7-bit ASCII. (36/7 == 5 plus a fraction, resulting
in 5 7-bit bytes and one waste bit in a word.) TENEX mode most likely packs 4
8-bit bytes into a word, wasting four bits per word. [I do not know exactly
what the setup is; beginning CS students on the PDP-10 I used weren't
made privy to network information, and I never got a chance to snarf
documentation on all the various data representations beyond RADIX-50 and
SIXBIT. Nevertheless, there are obvious arrangements.]
The original operating system for the PDP-10 was TOPS-10. Later on, a
modified version with extended features (VM paging?) was created; this was
TENEX. DEC then made their own version of TENEX; they called it TOPS-20;
the TENEX folks, not to be outdone, created TWENEX from TOPS-20. (After
which DEC decided to stop producing and supporting the PDP-10. Will UNIX
doom the VAX-11 in the same way?)
SINTEL20, by its name, runs TOPS-20. Same PDP-10 processor, therefore the
same word-to-bit translations apply as do for TENEX.
Now, can we kindly cut the TOPS-10/TENEX/TOPS-20 wars and get back to the
important stuff?
--
[Copyright 1987 Brandon S. Allbery, all rights reserved]
[Redistribution permitted only if redistribution is subsequently permitted.]
Brandon S. Allbery, moderator of comp.sources.misc and comp.binaries.ibm.pc
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