Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10 5/3/83; site intelca.UUCP
Path: utzoo!watmath!clyde!bonnie!akgua!mcnc!decvax!decwrl!amd!intelca!cem
From: cem@intelca.UUCP (Chuck McManis)
Newsgroups: net.arch
Subject: Re: Arbitrary byte alignment
Message-ID: <420@intelca.UUCP>
Date: Fri, 5-Oct-84 19:43:02 EDT
Article-I.D.: intelca.420
Posted: Fri Oct  5 19:43:02 1984
Date-Received: Sun, 7-Oct-84 09:11:52 EDT
References: <470@houxl.UUCP>
Organization: Intel, Santa Clara, Ca.
Lines: 26

One of the nicer things the DEC-10s and 20s had was something called a 
byte pointer. In this context a byte was any arbitrary grouping of bits
up to 16 I believe, but it may have gone up to 36, anyway the a string
of "bytes" had to start on an 36 bit word boundary but you could have
very long strings (ie all of a text file could be considered a string
of 7 bit bytes) There were several commands for using bytes notably
LDB, DPB for Load from byte pointer and Deposit to byte pointer, both
of these opcodes took an accumulator and an effective address of the
byte pointer, and transferred the byte to/from the lower (rightmost)
bits into/out of memory. It also took care of odd bits, (ie 5 7bit ascii
bytes would fit into a 36 bit word with one bit (the lsb) left over)
There were also autoincrement and autodecrement modes (this is DEC 
right ? :-)) and were quite convenient(sp?) for manipulating things 
smaller than a word. 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.
--Chuck

-- 
-- Chuck                                    - - - D I S C L A I M E R - - - 
{ihnp4,fortune}!dual\                     All opinions expressed herein are my
        {proper,idi}-> !intelca!cem       own and not those of my employer, my
 {ucbvax,hao}!hplabs/                     friends, or my avocado plant. :-}
                             ARPAnet    : "hplabs!intelca!cem"@Berkeley