Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site rlgvax.UUCP
Path: utzoo!linus!philabs!cmcl2!seismo!rlgvax!guy
From: guy@rlgvax.UUCP (Guy Harris)
Newsgroups: net.arch
Subject: Re: Arbitrary byte alignment
Message-ID: <171@rlgvax.UUCP>
Date: Sun, 7-Oct-84 01:11:16 EDT
Article-I.D.: rlgvax.171
Posted: Sun Oct  7 01:11:16 1984
Date-Received: Mon, 8-Oct-84 03:21:41 EDT
References: <470@houxl.UUCP> <420@intelca.UUCP>
Organization: CCI Office Systems Group, Reston, VA
Lines: 17

> One of the nicer things the DEC-10s and 20s had was something called a 
> byte pointer.... Memory was always accessed as a 36 bit word
> and the extraction was done in microcode I am pretty sure. I sure 
> wish some of todays processors were so talented and didn't need
> such archaic things such as byte, and word alignment with bytes
> fixed at 8 bits.

On the original KA10, a quick look at the timing would indicate that
an LDB or STB instruction did its work via the old trick of "shift and
mask"; the timings were dependent on how many bits you had to shift the
word right or left.  (The KA10 wasn't microcoded, and I don't think the
KI10 was, either; I don't remember whether the KL10 timings implied it was
done by shifting or not.)  You need a barrel shifter or somesuch to make it
doable in a fixed number of cycles.

	Guy Harris
	{seismo,ihnp4,allegra}!rlgvax!guy