harp@terra.pkg.mcc.com (Christopher North-Keys) (02/14/90)
An innocent user sent me the following, expecting to save money by loading a 4/390 with 100ns RAMs. This is not good. The 4/390's use 40 ns chips. The poor machine would not be a very happy puppy after such treatment, I don't think... |I found this on the Sun system administrator's bulletin board. Basically |what it says is that we should spec the 4MB memory SIMMs for use on |the Suns as 100ns access (or better), block (or "page') mode not required, |9 bits wide, physically mountable on a Sun 4/390 memory board. | || Date: Thu, 8 Feb 90 10:40:45 EST || From: bob@morningstar.com (Bob Sutterfield) || Subject: More memory to SPARCstation1 | || From: ks@tut.fi (Syst Kari) || Is access-time 100ns enough or should it be faster? | |That's fine. | | [ text deleted ] >From the Sun3 and Sun4/SPARC Hardware_Configuration_Guides, November 1989: (Cycle time is measured in nanoseconds.) Table 1-1 (excerpt) Sun-3 Sun-4 and SPARCsystems CPU/Memory Overview | | |----------Sun-3--------| |-Sun-4-| |--------SPARC---------| | 50 60 80 150 260 470 100 200 1 330 370 390 |MEMORY: |Err Detect bp bp bp bp ECC ECC par ECC |--synchronous parity--| |Cycle Time 270 200 100 270 80 30 70 60 50 |----- 40 ns -----| I returned the (hopefully accurate) response: Be sure to purchase memory with cycle times at or below specification for the target machine. Plugging in the wrong memory addition would cut the speed of the machine by a factor of at least two (I believe), effectively wasting an enormous amount of the purchase price of the machine. Puttin 100ns memory in a SS 390 would be idiocy. Note that even the SS1 uses 50 ns memory, rather than 100. Christopher North-Keys
shn@think.com (02/15/90)
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
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