PC Memory Population

[Steven_702]

I guess I need a refresher course because I actually used to build PC's for a living. But to be fair Dual Channel was just a white paper back then.

I have two 4GB DIMM in a PC that has 4 slots (two slots are currently empty.) They are installed in the below configuration.

They are in slots XMM2 and XMM4. I have verified this visually and via BIOS. This seems vaguely familiar and the PC operates fine.

However every utility I run tells me that "slot 1" and "slot 2" are populated while slots 3 & 4 are empty.

Anyway, I ordered the following Crucial RAM sticks because the configuator said they were compatible. http://www.crucial.com/usa/en/pavilion-hpe-h8-1240t-cto/CT8965273 I know they are a step up but my system supports them and I make purchases with future upgrades in mind when I can.

I need to know how to populate the slots with my new DIMMs. I am going to be a bit annoyed if I can't use the original 8GB of RAM because my purchase decision was based on the premise that I could keep and utilize them in the system. (24GB total)

It's okay if you want to discuss Dual Channel Population intricacies because I am actually interested but please, let's optimally configure my 4 memory sticks for the memory slots first.

Thank you.

 

[Eximo]

Generally you will see slots labeled as A1, B1, A2, B2 in that order from left to right. You populate the slots farthest from the CPU first, then skip a slot, and that would be it's dual channel pair.

When you get your memory kit, just install in the remaining two slots and it should stay in dual channel mode.

In your situation, they have labeled them 1-4 physically without matching pairs, while they are logically ordered in the BIOS. Haven't seen the XMM terminology used in a long time either. While they are Extended Memory Modules, these days they are usually just referred to as DIMMs or memory slots.

Some more technical caveats would be over population with double sided memory while at the maximum rating for the board. Example:

16GB max, 4 4GB double sided chips may not work, the last will have to be a single sided. An addressing problem. (Been a while since that has been a thing though)

 

[Calvin7]

This .pdf is a manual for another Z75 chipset motherboard. Read page 20.
http://asrock.pc.cdn.bitgravity.com/Manual/Z75%20Pro3.pdf

Combining multiple kits, the buy a couple sticks now and more later approach is not guaranteed to work.

G. Skill FAQs:

Q:
I want to install more memory, in addition to my existing memory kit. What are my options?

A:
We do not recommend mixing memory kits, regardless of brand or model.

By mixing memory kits together, there may be compatibility issues such as unable to boot or unable to operate at rated specifications.

Each of our memory kit are thoroughly tested to ensure compatibility within each memory kit. And because we have not tested our memory kit with your existing memory kit, we cannot guarantee compatibility when multiple kits are used.

**********************************************************************************

This holds true for other memory manufacturers also. A work around to installing multiple kits is to try running the memory at a lower clock speed.

 

[Steven_702]

Generally you will see slots labeled as A1, B1, A2, B2 in that order from left to right. You populate the slots farthest from the CPU first, then skip a slot, and that would be it's dual channel pair.

When you get your memory kit, just install in the remaining two slots and it should stay in dual channel mode.

In your situation, they have labeled them 1-4 physically without matching pairs, while they are logically ordered in the BIOS. Haven't seen the XMM terminology used in a long time either. While they are Extended Memory Modules, these days they are usually just referred to as DIMMs or memory slots.

Some more technical caveats would be over population with double sided memory while at the maximum rating for the board. Example:

16GB max, 4 4GB double sided chips may not work, the last will have to be a single sided. An addressing problem. (Been a while since that has been a thing though)

Your "A1, B1, A2, B2" slot order is what I recall from "back in the day..." But I would have been using MB instead of GB sticks. Heh. And the slots would have been filled because four 2MB SIMMs would have been about $100.00 cheaper then two 4MB SIMMs, but it still would have set you back about $800.00 retail.

Anyway the point is I never had to worry about upgrading empty slots!

Two slots placed directly next to each other and numbered "1&2" but not being the same channel certainly confusing.

I realize there is no guarantee that they will play well together but from what I could find online indicated that they "should." But I have smelled the acrid aroma of smouldering silicon, gallium and arsenic on more than on occasion.

BIOS tells me XMM1 & XMM3 are empty while 2&4 are populated. I meant to mention that.

Thank you.

 

[Steven_702]

This .pdf is a manual for another Z75 chipset motherboard. Read page 20.
http://asrock.pc.cdn.bitgravity.com/Manual/Z75%20Pro3.pdf
Combining multiple kits, the buy a couple sticks now and more later approach is not guaranteed to work. ...

I appreciate your warnings and that was certainly a concern of mine, however Crucial technical said these sticks would self-adjust to a higher voltage and lower clock frequency to match the other channel as needed.

I realize it is still a crapshoot so I thank you for taking the time to comment.

 

[Steven_702]

They seem to be compatible. They all run at the lower clock speed.

My Motherboard slots had XMM1, 2, 3, 4 written on it. 2&4 had the initial two memory sticks.
Slots 2&4 were black and 1&3 were deep blue, so that would have seemed to indicate where the matched pairs should go (which is how they are.)

BIOS however... still confuses me. It now says:
"Channel A - XMM1: 8GB - XMM2: 4GB
Channel B - XMM3: 8GB - XMM4: 4GB"

So that seems cockeyed. Maybe it's because my system (supposedly) uses UEFI, which I have no knowledge of how that works.
I still upgrade my BIOS on occasion but my System Information says UEFI

 

[Eximo]

Interesting. I would say go by the colors of the slot as that is usually how they do it. Does the BIOS splash say dual channel mode is on?

I did something similar with a DDR2 system. 2x2 and a 2x4GB kit. All Corsair XMS2 as I recall and that worked fine. Since then I have pretty much bought the amount of ram I intended to keep from the start.

 

[Steven_702]

Interesting. I would say go by the colors of the slot as that is usually how they do it. Does the BIOS splash say dual channel mode is on?

I did something similar with a DDR2 system. 2x2 and a 2x4GB kit. All Corsair XMS2 as I recall and that worked fine. Since then I have pretty much bought the amount of ram I intended to keep from the start.

I guess my earlier explanation was inadequate and confusing (I was tired.)

They are populated in matched pairs in like color slots.
~The 8GBs are in blue slots and the 4GBs are in black slots.
~XMM1 & 3 are blue, 2 & 4 are black.
~XMM1 is closest to the CPU, but 2 & 4 slots were & are holding the original sticks.

The POST splash & the BIOS System tab mirror each other.
They read:
(4-5 lines of irrelevant specs followed by😉
MEMORY 24GB / 1333 MHz / DUAL CHANNEL
Channel A - XMM1: 8GB - XMM2: 4GB
Channel B - XMM3: 8GB - XMM4: 4GB

But since it just says "DUAL CHANNEL" I am left wondering if that just means dual channel capable or dual channel operational.

I usually fill and max the banks as well, but I was getting creative to keep from breaking the bank because I purchased an RX 480 GPU at the same time.

Honestly, there is such a minor increase I think I will pull the old DIMMs and PassMark with just the new DIMMs. (I will change slots!)

My new DIMMs are DDR3L-1600 PC3L-12800 (system compatible) but they are being throttled down to match the DDR3-1333 PC3-10600 legacy sticks.