Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!husc6!necntc!ames!orville!fouts
From: fouts@orville.UUCP
Newsgroups: comp.arch
Subject: Re: 64 Vs 32
Message-ID: <755@ames.UUCP>
Date: Sat, 14-Mar-87 13:29:16 EST
Article-I.D.: ames.755
Posted: Sat Mar 14 13:29:16 1987
Date-Received: Sun, 15-Mar-87 04:01:08 EST
References: <3810013@nucsrl.UUCP> <985@rpics.RPI.EDU>
Sender: usenet@ames.UUCP
Reply-To: fouts@orville.UUCP (Marty Fouts)
Organization: NASA Ames Research Center, Mountain View, CA
Lines: 24

In article <985@rpics.RPI.EDU> yerazuws@rpics.RPI.EDU (Crah) writes:

>Yep.  Consider- it's now a standard configuration for VAX 8800's
>to come with 512 megs of memory (I've got the part number around
>somewhere).  A VAX has 32 bits- so if we assume (*) that all 32
>can be used as memory address, a VAX (or other 32-bit processor)
>can have AT MOST 4 GIG of memory.
>	

Although this is true, historically when the limit is first reached,
processors aren't redesigned to use larger address spaces, but rather
work arounds are found.  When 16 bits wasn't enough address space for
micros, "bank selection" was utilized.  There are machines around
which use 24 bit addresses and manage > 24 bit memory spaces by
segmentation (IBM), or memory hierarchy (Cray).  Another possibility
is to change the granularity of address.  A word addressable 32 bit
word VAX is more likely than a byte addressable 64 bit VAX, and that
alone buys 3 more doublings in memory size.

Besides, with 4Mb memory chips, 4Gb is still (not counting ECC) 8
THOUSAND chips; so we aren't likely to see very many machines with
that many memory parts, soon.

I still hold out for ten years, if at all.