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From: rpw3@rigden.wpd.sgi.com (Rob Warnock)
Newsgroups: comp.arch
Subject: Re: 64 bits
Message-ID: <67215@sgi.sgi.com>
Date: 18 Aug 90 03:55:21 GMT
References: <9660@ganymede.inmos.co.uk> <12502@encore.Encore.COM> <15674@thorin.cs.unc.edu>
Sender: rpw3@rigden.wpd.sgi.com
Reply-To: rpw3@sgi.com (Rob Warnock)
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 25

In article <15674@thorin.cs.unc.edu> prins@prins.cs.unc.edu (Jan Prins) writes:
+---------------
| jkenton@pinocchio.encore.com (Jeff Kenton) writes:
| |>use that memory.  Right now, zeroing memory on a 16Mbyte machine takes
| |>a noticeable number of seconds.  Will machines be 1000 times faster by
| |>the time we have 1000 times more memory?
| A machine with a lot of physical memory need not be restricted to have
| a single processor....  To "zero" all of the memory, use all of the 
| processors; it should take less than a second.
+---------------

Nor, for bulk clearing (which is a major overhead for many Unices), do you
have to clear with plain CPU instructions. For example, suppose your memory
is N-way interleaved. It's practically free to add some magic to the memory
controller that lets the CPU store "N" words at a time with the same value
(by cycling all N memories in parallel). Then you can clear in 1/Nth the time.

Other tricks include using DMA or graphics devices to clear memory for you.

Assuming a memory 64 bits wide, 8-way interleaved, clearing with some kind
of hardware-assisted "page mode" access, and a 40ns page mode cycle time on
the RAM, you can clear at a rate of 0.67 sec/Gbyte, or 10.7 seconds for 16 GB.
[If I've done my arithmetic correctly... ;-}  ]

-Rob