Z87X-UD4H-CF: Mix Memory Sizes?

Z87X-UD4H-CF mobo, socket 1150 LGA.

Currently have 8 gigs occupying 2 slots (i.e. 2 4-gig memory module)

2 more slots are currently empty.

If I add memory, do I have to add two more 4-giggers?

Or could I, for instance, put an 8-gig module in each of the two
unoccupied slots giving me a total of 24 gigs instead of just 16?
--
Pete Cresswell

(PeteCresswell) wrote:
Z87X-UD4H-CF mobo, socket 1150 LGA.

Currently have 8 gigs occupying 2 slots (i.e. 2 4-gig memory module)

2 more slots are currently empty.

If I add memory, do I have to add two more 4-giggers?

Or could I, for instance, put an 8-gig module in each of the two
unoccupied slots giving me a total of 24 gigs instead of just 16?

The Intel Flex memory feature, really allows a lot of
different configurations. But I'm not aware of any
separate documents any more, that outline the possibilities.

At the very least, you can try "matching across channels".
You've done that already, by using 2x4GB and placing one
4GB module on each channel.

Channel 0 Channel 1 Channel 0 Channel 1
| | | |
4GB 4GB 4GB 8GB
| | | |
8GB 8GB 8GB 4GB

(Traditional non-Flex (Flex memory allows you
setup required positional to do it like this. No
matching...) positional requirement, but match quantity)

If you use 2x4GB plus 2x8GB, the 4GB modules are
likely single-sided (single rank) DIMMs. The 8GB
modules are double-sided. So that's the difference
in construction. There should be no problem
mixing them. The reason this is the case, is they
make both module types with the same memory chips.

And are you absolutely sure you need the memory ?
Did you check for "peak usage" on the machine,
and decide you regularly go over 8GB ? I have a
machine that I added a lot of memory to, and it
was to solve one particular use case. And my purchase
isn't "rational" as a result. The last rational
purchase I made, was taking a system from 1GB total to
2GB total, where I regularly used a bit more than
1GB. And that purchase made sense. I doubt the
several purchases since then, I could really
justify.

Even the clerk at the store I was dealing with,
"asked me if I was a gamer". So I explained to
him what I was doing, and that I wasn't a gamer
who "wanted to max out the memory because it
would make Crysis run faster". So don't be surprised
if a store clerk also tests your reason for
buying the memory.

*******

If the memory is high-speed memory, and you're
using XMP, the XMP information stored in the DIMM
is for a single pair. Not a lot of memory uses
the second profile to handle two sets of memory.

For example, I want to buy a 2x4GB kit, and they're
XMP. With XMP disabled, the RAM runs DDR3-1866,
and the voltages aren't boosted. If I enable the
XMP setting in the BIOS, the VDimm rises to 1.65V
on its own, and the memory is set to DDR3-2400 for
me. So XMP makes it easy to set up a memory to the
"enthusiast" speed it is rated for.

However, if you try and fill all slots, the second
profile storage area in the DIMM doesn't handle that
case. The two profiles may consist of the same profile
information, one profile with Command Rate 1, and the
other profile with Command Rate 2. And really, it's normal
now for Command Rate 2 to be used for everything.
What Command Rate 2 does, is cause the RAS and CAS
transfer phases to last for two cycles, to give
lots of Tsetup for the transfer of an address value,
into the memory chips. Command Rate 1 uses one less
bus cycle, but the timing windows is quite small, and
the chances of memory errors is higher. So wasting
a profile entry on Command Rate 1, is kinda silly.
I didn't realize what was in the Profile storage,
until I checked with CPUZ from cpuid.com.

If the second XMP profile actually had info needed
for a four DIMM configuration, that might be
an opportunity to match all four DIMMs. But since
that isn't a common feature, it's hardly worth
shopping for it.

When you put in your 2x4GB plus 2x8GB setup,
you can leave things at Auto, and it'll work
without help. Maybe it will choose DDR3-1333
for example. If the rated speed of the memory
is higher, you'll need to take things off
Auto and dial in some manual values. And that
isn't nearly as easy. On my system here,
using half the memory slots, I could run
at DDR3-2400, using all slots all I could
manage was DDR3-1866 (with manual adjustment).
I tried DDR3-21xx speed and I couldn't pass
Prime95. And I didn't feel like cranking
the hell out of VCCSA or VPLL. So you will have
some fun tuning up your system, if you want to
make it run at the full rated speed (whatever
that is). And these days, those sorts of tweaks
(DDR3-2400) don't make nearly as much difference
as they used to.

[VCCSA is the voltage feeding the System Agent.
VPLL or "phase locked loop" probably affects the
amplitude of the clock signal feeding each rank
on the DIMM.]

http://media.bestofmicro.com/sandy-b...Y-275038-3.jpg

Paul

Per Paul:
And are you absolutely sure you need the memory ?
Did you check for "peak usage" on the machine,
and decide you regularly go over 8GB ?

"Absolutely" is too strong a word, but when I open up a utility called
Process Lasso, it shows a "RAM Load" graph that is regularly pegged.

This is my 24-7 machine that acts as a IP camera server and a media
server. Since adding a couple more IP cams, the memory has gone up
significantly.

Do I need 24 gigs? Absolutely not..... 16, yes... 24, no.

But I was thinking along the lines of "What if I do need more than 16
sometime later, do I want to be stuck with throwing away a couple of
perfectly-good 4-gig memory modules?".

OTOH, installing 8 gigs of memory that I don't need could be construed
as throwing it away....

So, question/answers aside, I will probably stick with putting another 8
gigs instead of 16 in there.
--
Pete Cresswell