[SOLVED, SORT OF] RAM memory reported is less than installed

Vieri · l33t Joined: 18 Dec 2005 Posts: 877

Hi,

I have an ASROCK A75 Pro4 motherboard with the latest BIOS version P.2.50.

I used to have 2 Corsair 2GB RAM modules, and they worked just fine in slot 0 & slot 2 (total 4GB RAM).

I recently installed an extra 2GB RAM module with similar specs but different brand.

There are 4 DIMM slots on the board, and my original 2 RAM sticks were always in slot 0 and slot 2. I'm not a hardware expert, but I noticed that when I insert my new RAM stick in slot 1 (slot 3 is empty), BIOS reports "Single-Channel Memory Mode". However, if I move it to slot 3 (leaving slot 1 empty), BIOS reports "Dual-Channel Memory Mode". Why is that?

In any case, no matter where I insert my new RAM, the BIOS reports 3 x 2GB for a total of 6GB.
However, no matter which OS I boot (tried the latest Gentoo live minimal image and other Linux flavors) I can only see 4GB (top, free, etc.).

Here's the output of dmidecode regarding the DDR3 sticks:

tomtom69 · Posted: Wed Oct 17, 2018 6:43 pm Post subject:

your board handbook says

Anon-E-moose · Posted: Wed Oct 17, 2018 7:00 pm Post subject:

As far as the OS memory report are they 64 bit OS's or 32 bit, if 32 then they will only report 4gb.

I haven't looked at the manual for the MB, but typically if you put an odd amount of memory 1,3, etc, then you don't get dual channel memory.
Some MB's have a setting in the bios to switch from dual to single, an odd amount HAS to run in single (if you think about it, it's obvious)
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freke · Posted: Wed Oct 17, 2018 7:56 pm Post subject:

It's only using two of the DIMMs - they're supposed to be installed in pairs for dual-channel configuration. ie. two or four, but not three DIMMs

Naib · Posted: Wed Oct 17, 2018 8:04 pm Post subject:

Is this a 32bit system or a 64bit system?
The reason I ask is

Anon-E-moose · Posted: Wed Oct 17, 2018 8:21 pm Post subject:

There's 2 or 3 things going on.

if you have memory slots 1 2 3 4
1 and 3 are dual channel, 2 and 4 are dual channel.

you can put memory in 1 2 and 3 but you'll only have single channel with an OS potentially seeing max of 6 gb.
you can put memory in 1 3 and 4 again only single channel, the bios will report 6 because it sees it, but an OS isn't likely to see channel 4 thus reporting only 4 gb.

And as I and others have said if the OS is 32 bit it only sees 4gb max no matter how much is really available.
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PRIME x570-pro, 3700x, 6.1 zen kernel
gcc 13, profile 17.0 (custom bare multilib), openrc, wayland

Vieri · l33t Joined: 18 Dec 2005 Posts: 877

Thanks for the feedback.

I first booted with Gentoo's minimal install CD on a bootable USB pendrive.
It was 64-bit.

I am now running an Ubuntu system and here's the output of uname:

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

The manufacturer will test memory configurations that they list in the book. Other configurations may work but there is no guarantee.

You can, if the board supports it, put a single stick in, but putting 2 in one bank and 1 in the next is an oddball case that almost no motherboard manufacturer will actually test, especially if one module is not identical to the others.

I have mixed brands before, but in almost every case if all sticks aren't the same exact size (of RAM) then something unfortunate will usually happen. Like it decides all the sticks are the size of the smallest, if you're lucky, or maybe that it shouldn't boot all, or only recognizes the first stick.

I've had a motherboard that work with two different module sizes, but each bank must have identical modules in that bank (0 and 2, 1 and 3) and the lowest-numbered bank is supposed to have the biggest sticks if I remember right. I think that board was an Asus. I remember playing around with that one having found some dimms for cheap online, and didn't get happy results.

I've also mixed timings before, but again identical timings in the same-color slots. The board may decide all the timings are the same as the worst modules.

Naib · Posted: Wed Oct 17, 2018 9:04 pm Post subject:

Anon-E-moose · Posted: Wed Oct 17, 2018 9:04 pm Post subject:

Again, I haven't read the MB manual, but if you have 0,1 and 2 populated then you will ONLY get single channel
If the bios allows you to set memory as dual or single and you have 3 sticks then it will probably ignore the 3rd stick when offering it to an OS, if it's set to dual.

And it could be that it simply won't offer the 3rd stick as usable if only 3 are available.

A lot of what I'm conjecturing depends on how the bios is written. And it's been years since I've used an asrock board.

As far as adding another stick to match the odd one, it should work.
They don't have to be the same manufacturer (though it's recommended and they probably only test for that) but if the specs are the same it should work.
_________________
PRIME x570-pro, 3700x, 6.1 zen kernel
gcc 13, profile 17.0 (custom bare multilib), openrc, wayland

Vieri · l33t Joined: 18 Dec 2005 Posts: 877

NeddySeagoon · Posted: Thu Oct 18, 2018 7:24 pm Post subject:

Vieri,

You are trying to mix RAM with different 'geometries'. That may or may not work. It depends how tolerant the memory controller is.

RAM is divided into 'rows' and 'columns'. Your single sided stick has only half, or a quarter the number of RAM chips on it compared to the double sided sticks.
As the two sorts are both 2GB, The single sided stick requires one or two extra address bits per chip over your double sided sticks.

Some DRAM controllers will work, some won't as they expect all the the DRAM to have the same number of rows and columns.
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NeddySeagoon

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