SUMMARY: Question on memory on a SPARC1000

From: Chatch Ingersoll (
Date: Tue Sep 03 1996 - 13:45:14 CDT


        Well I got some answers on my question about SPARC 1000 memory. The
general concensous was to use memory interleaving, but it seems that there
are some Sun engineers who say it doesn't make a difference. We were told
by a Sun engineer that all memory should be placed on the same board, so we did.I will be seting up the memory interleaving soon on our 1000 and will see if there is a difference. Also you can add CPU's one at a time. I encluded all
of the responses.

Thanks alot,


Hi Chatch.

In message <>you write:
>Please help settle an arugument. We have a SPARC 1000 with 2 CPU on board0
>and 2 CPU on board1. We have all 512 MB of memory on board0 and none on
>board1. Should memory be spread to both boards?

Hmm... Interesting. I'm curious what other people have to say about this, but
I'd guess that it would be better to spread the memory around evenly.
Otherwise the CPU's on the memory-less board would have to cross the xdbus to
reference memory. Just a hunch

 Or is it better to keep
> it all on one board. Also can we add a fifth CPU to board2 or do we ha
>to add two at atime?
No and No. You can add 1 CPU at a time, but each board can only hold 1 CPU, so
you'd have to add a third board if you want a 5th CPU.


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Can add 1 CPU at a time. Best to spread memory. It enhances recovery options as well as performance. Need more memory ? Buy Kingston it is a good value. Regards Tom Ryan

Was told by a Sun engineer that you should balance the memory to better balance the machine.

We have our memory balanced between processors on our 1000:

System Configuration: Sun Microsystems sun4d SPARCserver 1000 System clock frequency: 40 MHz Memory size: 512Mb Number of XDBuses: 1 CPU Units: Frequency Cache-Size Memory Units: Group Size A: MHz MB B: MHz MB 0: MB 1: MB 2: MB 3: MB --------- --------- ----- ----- ----- ----- Board0: 60 1.0 60 1.0 128 128 0 0 Board1: 60 1.0 60 1.0 128 128 0 0 ======================SBus Cards=========================================

When we added additional CPUs and memory to our S1000, we were told by Sun engineers that while there is nothing wrong with adding units to only one board, it is much better to always distribute evenly across the system boards. This takes advantage of the extra buses and memory channels that would otherwise go unused.

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I spent 5 years working for Sun and I can tell you SPILT UP THAT MEMORY!!!

The manner in which the system utilizes its memory makes it more efficient when the memory is divided up across the system boards.


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Memory is interleaved across boards - and is best located equally between systems....populate group 1 on board 0 first, group 1 on board 1 next, etc....

Same goes for CPU's....cpu0 board 0, cpu0 board 1.....and SBus too. This way boards share the tasks somewhat evenly....

Each system board for a SS1000 only holds two cpu's so with two system boards you can only put in 4 cpu's.....

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well - what I can tell you is that we we had our 1000E installed - 512 Megs of RAM - 3 motherboards - the Sun engineer took great care to try and *BALANCE* the memory across boards - we ended up with 128 on boards 2 and 3, and 256 on board 1 - I believe the idea was to try and minimise the amount of memory fetch traffic going over the bus (xdbus???) connecting the motherboards (bearing in mind that we have processors on all 3 boards)

I can see the sense in what he was saying, but have no idea on the actual effect if you dont follow that advice.

Hope this helps,

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Our 1000 (not a 1000E) came with a hardware guide that tried to explain memory interleaving. I've also run a 1000 with 7 CPUs, so an odd number can be supported.

I think once you've studied the hardware guide there maybe an advantage in going for 2 way memory interleaving by placing 2 lots of 128MB in the same memory group, e.g. 0 and 1. Whether there is any advantage of spreading the two groups across the 3 motherboards (bandwidth?) I'm not sure. You will of course need that guide to work out which simm slots match which groups.


A: MHz MB B: MHz MB 0: MB 1: MB 2: MB 3: MB --------- --------- ----- ----- ----- ----- Board0: 85 1.0 85 1.0 128 128 0 0 Board1: 85 1.0 85 1.0 128 128 0 0 Board2: 85 1.0 0 0 0 0

or maybe

A: MHz MB B: MHz MB 0: MB 1: MB 2: MB 3: MB --------- --------- ----- ----- ----- ----- Board0: 85 1.0 85 1.0 128 0 0 0 Board1: 85 1.0 85 1.0 0 128 0 0 Board2: 85 1.0 128 128 0 0



I've never seen a system with an odd number of CPUs, so my guess is that this isn't supported (although it may work).

As for splitting the memory, I've gotten different responses from different Sun engineers about this too, so my guess is that it doesn't make that much difference.

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1 ) memeory should be split across the two boards ( but not three ). memory interleaving works on pairs of boards, across the groups. so use group 0 on both boards, then group 1 , ... the third and fourth boards are paired in the same way. note - to work correctly the match the memory simms across the boards. 2 ) of course you can add the CPUs singly.


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