Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!rice!sun-spots-request
From: shn@think.com
Newsgroups: comp.sys.sun
Subject: Re: CRITICAL CORRECTION to [More memory to SPARCstation1]
Keywords: Hardware
Message-ID: <5017@brazos.Rice.edu>
Date: 15 Feb 90 15:51:47 GMT
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Organization: Sun-Spots
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X-Refs:  Original: v9n39
X-Sun-Spots-Digest: Volume 9, Issue 44, message 2

First a simple point about memories for Suns.  If you put in DRAMS into a
Sun which are not fast enough, the Sun will either crash due to parity
errors or not run at all.  They do not "cut the speed of the machine by a
factor of at least two".  

There is some confusion about the relationship of "cycle time" and the
speed requirements of main memory.  All Sun 4s (and probably all Sun 3's
for that matter) use a two tiered memory scheme.  The fist tier is called
"cache memory" and is usually made of very fast Static Rams (SRAMS).  The
cache memory is designed to supply data (when possible) to the processor
in one clock cycle.  The second tier (a.k.a. Main Memory) is made up of
Dynamic RAMS (DRAMS) which are generally slower than SRAMS.

The Memory Management Unit (MMU) in the computer keeps track of which data
is in main memory and which is in the cache memory and moves the data
around to hopefully optimize the system performance. 

All Sun computers have a fixed amount of cache memory and the end user
cannot alter or modify the performance or amount of cache memory.  Most
Sun computers can have additional main memory added to the computer by
replacing DRAM chips with higher capacity memory chips, or adding
additional memory boards.  

I would like to offer the following advice about memory upgrades.  In
almost all cases, you are better off spending a little more money and
purchasing your memory upgrades from companies like Clearpoint, Helios,
Parity, or even Sun than purchasing SIMMs directly from electronic
distributors.  Most of these companies will give a lifetime warranty for
their products and give excellent service which will pay for it self in
the long run. 

#include <the-usual-disclaimer>

Sam Nuwayser - Thinking Machines Corporation, Cambridge, MA +1 617-876-1111
   shn@think.com, {harvard,bloom-beacon,topaz}!think!shn