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Re: Memory

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On 30/03/2017 22:18, Don Y wrote:
> I'm rebuilding an older server to act as my compile farm.  So, digging
> through
> my box of RAM to see what I can find that fits the bill.
>
> The documents for the machine indicate (emphasis mine):
>
>     DIMMs should be installed in matched sets of four. This enables
>     quad-channel operation and provides the highest memory bandwidth.
> The sets
>     of four must be MATCHED IN SIZE, RANK and ORGANIZATION. This
> information
>     can normally be found on the FBD label. For example, the label of
> each FBD
>     in a set of four might read: 1G 2R x8, in which 1G represents the
> size of
>     the memory module, 2R represents the number of ranks, and x8 represents
>     the organization.

You can always mount them and then see what SPD finds. What it says is 
generally true that putting odd sized ones in will be the worst possible 
performance (might not even work on some chipsets) pairs are better and 
on some boards quads are (slightly) better still.

If you care about ultimate memory bandwidth performance then you try 
hard to meet these criterion, but it can be expensive to get that last 
5-10% and with modern on chip multi level cache not always worthwhile.

Superfast (aka gaming) ram is generally not worth the extra money.
>
> It goes on to say:
>
>     They can also be installed in pairs of two; in this case, the computer
>     will continue to operate, but with a slight reduction in
> performance. The
>     pairs must be MATCHED IN SIZE, RANK and ORGANIZATION.
>
> Of course, the SPD devices contain far more information than that outlined,
> above.  So, its possible that devices can bear the same descriptive
> labeling
> yet not be matched *enough* to satisfy the first (vague!) criteria.

What tends to happen if they are the same size, rank and organisation 
but different speeds is that the system runs to match the slowest 
(rather than not running at all).

> Would not a better way of differentiating between these two (descriptively
> IDENTICAL) sets of criteria been to refer to "having identical part
> numbers"
> in the first case and "compatible *descriptions*" in the second?  I.e.,
> there
> are obviously more constraints at work in the first case that aren't
> highlighted in the description that is provided (which is identical to
> that of the second case).

I prefer pairs or quads from the same maker and batch that way you don't 
get any nasty surprises.
>
> [It would also be nice if the user had a way of knowing that he had/hadnot
> met those criteria as "a slight reduction in performance" is probably not
> the sort of objective symptom that most users could evaluate!]

SPD will tell you enough but otherwise write a memory intensive program 
or run a well known memory speed benchmark program to verify results.


-- 
Regards,
Martin Brown

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Memory Don Y <blockedofcourse@foo.invalid> - 2017-03-30 14:18 -0700
  Re: Memory John Fields <jfields@austininstruments.com> - 2017-03-30 19:12 -0500
    Re: Memory Don Y <blockedofcourse@foo.invalid> - 2017-03-30 17:27 -0700
  Re: Memory whit3rd <whit3rd@gmail.com> - 2017-03-30 17:50 -0700
    Re: Memory Don Y <blockedofcourse@foo.invalid> - 2017-03-30 18:02 -0700
      Re: Memory whit3rd <whit3rd@gmail.com> - 2017-03-30 20:40 -0700
        Re: Memory Don Y <blockedofcourse@foo.invalid> - 2017-03-30 23:55 -0700
      Re: Memory Martin Brown <'''newspam'''@nezumi.demon.co.uk> - 2017-03-31 08:44 +0100
        Re: Memory Don Y <blockedofcourse@foo.invalid> - 2017-03-31 01:51 -0700
          Re: Memory whit3rd <whit3rd@gmail.com> - 2017-03-31 16:39 -0700
  Re: Memory Martin Brown <'''newspam'''@nezumi.demon.co.uk> - 2017-03-31 08:01 +0100
    Re: Memory Don Y <blockedofcourse@foo.invalid> - 2017-03-31 01:42 -0700
      Re: Memory Don Y <blockedofcourse@foo.invalid> - 2017-03-31 12:11 -0700
        Re: Memory Don Y <blockedofcourse@foo.invalid> - 2017-03-31 12:15 -0700

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