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From: Paul 
Newsgroups: microsoft.public.windowsxp.general
Subject: Re: Dell 780 Problem:
Date: Fri, 24 Nov 2017 09:49:50 -0500
Organization: A noiseless patient Spider
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Mark Twain wrote:
> Assuming that after testing both DIIMS
> and they turn out OK. Would it be beneficial
> to add another set of 2x2GB DIMMS?
> 
> 
> How do you know which to choose?
> 
> 
>
https://www.google.com/search?q=2gb+dimms&source=lnms&tbm=shop&sa=X&ved=0ahUKEw
j6z7_ppdfXAhXhj1QKHatoDWQQ_AUICigB&biw=1700&bih=914
> 
> https://www.staples.com/2gb+dimms/directory_2gb%2520dimms
> 
> Thanks,
> Robert

For those playing at home, this is Windows 7.

Windows 7 x64 will comfortably use 1GB for the OS portion.
In your case, with 2x2GB installed, this leaves 3GB
for application usage.

Do you think you will need more RAM for say Firefox ?
I haven't checked while my copy of Firefox is running
lately, to see if it uses more. I know in one experiment
some time ago, related to your interest in Yahoo News,
I got Firefox using 1GB of RAM while visiting that page.
In a second test, I could no longer reproduce such a
high usage. It uses a lot less now.

So there may be times you need more RAM. I can't really
guess at what your "worst case" usage pattern is.

I'm on WinXP with 3.2GB of RAM or so to play with, and
I haven't really had a problem yet with running out.
That's the limit of my 32 bit OS on it. (I have other
OSes I use, but WinXP is my "daily driver".)

While there's probably some tool to look for the
"Commit Peak" on Windows 7, you have to collect operational
data for a few days to get some idea what your peak usage is.

I personally prefer to do this by "dead reckoning", using
what I know about each application to chart usage. And then
decide whether more RAM is required.

*******

In "lucky cases", something is written on the RAM sticks,
which may help when making future purchases. Like a label
that gives the timing ("5-5-5-15") as well as a speed ("DDR3-2400").
Then, when you go shopping, you have some idea.

Other options include consulting the Crucial.com or Kingston.com
search pages. There, you can enter model info and find out what
to use.

http://www.crucial.com/usa/en/compatible-upgrade-for/Dell/optiplex-780-desktop

The densest option there is 2x4GB for $75 or so. The 2x2GB
kit is a bit cheaper. There should be four items listed for
sale on that previous link (click the button to show them).

http://www.crucial.com/usa/en/optiplex-780-desktop/CT7339271

     DDR3L-1600
     Total Capacity: 8GB Kit (4GBx2)
     Specs: DDR3 PC3-12800 CAS 11  UDIMM (unbuffered) NON-ECC DDR3-1600 1.35V

Now, the thing is, that is DDR3L at 1.35V and not the same
as regular DDR3 at 1.50V. Can you mix them ? Does the VDIMM
auto-switch or does it always run the DIMMs at 1.5V ? Dunno.
I think my DDR3 here runs 1.5V and I don't even know if
mine (my newest machine) even supports DDR3L.

If you bought 2x4GB, you could pull the 2x2GB set and just
run the 2x4GB set. As an example of side-stepping the issue.

Summary:

1) Demonstrate the need first. Using Task Manager, what is
    your Commit Peak. Or alternately, just watch RAM usage when
    several browsers or programs are open and see how much you
    are using.

2) It's nice if the RAM types match. I think 1.35V RAM can run
    at 1.5V, but I doubt 1.5V RAM is all that happy at 1.35V.
    And I don't know what mechanism the system uses to decide
    what to do. It can read the SPD before programming the chip
    registers, which also gives it a chance to change the voltage
    if it wants. I don't really know if 1.5V systems just stick
    with 1.5V and leave it at that. So you would want to collect
    more info about the RAM you've currently got.

A copy of CPUZ from here, can dump some info about the RAM.
But the info isn't the same as the "label" on the RAM. It's
techie info that's hard to map backwards to actual brand
and SKU info. But this is about the best I can do for an
electronic utility to read out the DIMMs.

https://www.cpuid.com/softwares/cpu-z.html

The first purple download link is an EXE installer,
so leaves a permanent copy in Program Files.

The second ZIP version, you run that as a portable folder.
You unpack the ZIP into a folder in your downloads, and
when you run the EXE file, it should just open a window
with the hardware details. Those are the available choices.

It has a memory tab, so you can list the techie details
of the sticks. It should include timing and speed. For
the clock speed, you take the number from the CPU info
and double it. An 800 clock listing would be DDR3-1600
RAM. Several timings will be listed, and the set with
the largest numbers is probably the "full speed"
timing set.

The machine I'm typing on, the CAS6 DDR2 died on it,
and I got a chance to buy some more. And I got some
slightly faster CAS5 DDR2 with the same clock speed.
If there's a speedup effect, I can't see it :-) .
And on even more modern machines, these CAS timing details
seem to be making less and less of a difference.

*******

https://en.wikipedia.org/wiki/Dell_OptiPlex

    780 (Yr.2009) Q45  DDR3-1066/1333    (Intel AMT features disabled)

A DDR3-1600 stick would just gear down to the
slower speed. And the BIOS adjusts the CAS
accordingly.

It says the 780 is DDR3, which tells me the memory
slots run at 1.5V and so 1.35V RAM should run OK
in there. The 1.35V RAM is supposed to tolerate 1.5V.
I expect this is why Crucial lists it as compatible.

https://en.wikipedia.org/wiki/DDR3_SDRAM#DDR3L_and_DDR3U_extensions

    The DDR3L and DDR3U specifications are compatible with the original
    DDR3 standard and can run at either the lower voltage or at 1.50 V.[19]

HTH,
    Paul
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