Path: ...!weretis.net!feeder9.news.weretis.net!news.misty.com!news.iecc.com!.POSTED.news.iecc.com!not-for-mail
From: John Levine <johnl@taugh.com>
Newsgroups: comp.arch
Subject: Re: bit addressing Byte Addressability And Beyond
Date: Wed, 1 May 2024 17:53:05 -0000 (UTC)
Organization: Taughannock Networks
Message-ID: <v0tvi1$1n3a$1@gal.iecc.com>
References: <v0s17o$2okf4$2@dont-email.me> <v0s744$l3v$1@gal.iecc.com> <jwvcyq5qzxr.fsf-monnier+comp.arch@gnu.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Injection-Date: Wed, 1 May 2024 17:53:05 -0000 (UTC)
Injection-Info: gal.iecc.com; posting-host="news.iecc.com:2001:470:1f07:1126:0:676f:7373:6970";
	logging-data="56426"; mail-complaints-to="abuse@iecc.com"
In-Reply-To: <v0s17o$2okf4$2@dont-email.me> <v0s744$l3v$1@gal.iecc.com> <jwvcyq5qzxr.fsf-monnier+comp.arch@gnu.org>
Cleverness: some
X-Newsreader: trn 4.0-test77 (Sep 1, 2010)
Originator: johnl@iecc.com (John Levine)
Bytes: 2447
Lines: 28

According to Stefan Monnier  <monnier@iro.umontreal.ca>:
>>> I guess the idea of  going all the way down to bit-level addressing
>>>was considered a bit  extreme? 
>>
>> STRETCH had bit addressing. It added a great deal of complication for
>> very little benefit. In the relatively rare situations where you want
>> to handle bit fields, shifting and masking is good enough without
>> slowing everything else down.
>
>Bit addressing doesn't have to be expensive: the DEC Alpha could have
>decided to use bit-addressing simply by ignoring/trapping more of the
>lowest bits than it did.

That would waste three bits in every address, which would have been
phenomenally expensive in the 1960s when every byte cost real money.

The 360 had 12 bit displacements, so you could address a 4K range
without having to load another base register.  This would shrink
it to 1K, so as a first approximation you'd need four times as
many base register loads.  Nope.

I agree that with 64 bit addresses and memory that is pennies per
megabyte the tradeoffs are different but that horse left the barn 50
years ago.  And I still don't think that bit operations are common
enough to be worth using bits in every non-bit address.
-- 
Regards,
John Levine, johnl@taugh.com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly