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Date:      Thu, 11 Jan 2018 09:02:07 -0600 (CST)
From:      "Valeri Galtsev" <galtsev@kicp.uchicago.edu>
To:        "Lowell Gilbert" <freebsd-questions-local@be-well.ilk.org>
Cc:        "Aryeh Friedman" <aryeh.friedman@gmail.com>, "FreeBSD Mailing List" <freebsd-questions@freebsd.org>
Subject:   Re: OT: Max system physical memory
Message-ID:  <50615.108.68.170.208.1515682927.squirrel@cosmo.uchicago.edu>
In-Reply-To: <44wp0ofr1w.fsf@be-well.ilk.org>
References:  <CAGBxaX=+YUuDBOp5n1Kjq6xaJmjEpZ8kWARNMnE_3LwBkNM6GA@mail.gmail.com> <44wp0ofr1w.fsf@be-well.ilk.org>

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On Thu, January 11, 2018 7:44 am, Lowell Gilbert wrote:
> Aryeh Friedman <aryeh.friedman@gmail.com> writes:
>
>> My computer (HP Pavilion P7-1234, FreeBSD 11.1-RELEASE [amd64]) has 2
>> 240
>> pin DIMM (DDR3, PC3-10600) the manual says the max memory is 8 GB but I
>> see
>> some 16 GB packages (2x8GB).   If I put one or two of these in will it
>> see
>> the extra memory?
>
> Probably not.
>

It is hit and miss. It is possible that specifications were written based
on largest available modules at the moment of writing. If replacement
modules are compatible with memory controller (i.e., say, the same
PC3-10600), it is possible they will work. There still is the chance they
will not work reliably, _IF_ there are some less trivial specs of memory
controller are involved. Such may be: bus amplifiers may only handle up to
this capacitive load before signals go out of specs. In general, larger
RAM has larger numbers of address inputs connected to given lead, which
may entail larger capacitive load. System board layout may have its impact
here as well. Apart from that (and maybe some internal schematic specifics
of memory controller), there is nothing fundamental about 8 GB RAM limit,
so it may work. But chance is it will not.

In any case, don't mix RAM modules with different specs (look at timing
details like CL as well) on the same memory bus.

I hope, this helps.

Valeri

++++++++++++++++++++++++++++++++++++++++
Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247
++++++++++++++++++++++++++++++++++++++++



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