Only seeing 4Gb RAM with 8Gb installed., old 775 rig.

Scania · 2 Sep 2019 at 10:36

I have built an old Sct 775 system up via the MM and it has 8Gb Patriot DDR 2 667, 2x4Gb sticks, trouble is I can only get it to recognise 4Gb, I’ve tried both sticks individually and in all four RAM slots without issue but if I put both sticks in together one seems to be ignored in both the BIOS and Windows (10 Home x64)

I’m wondering if I’m doing something wrong, I’m a bit rusty on DDR2 to put it mildly, it’s in an Asus P5k-e board with a Q9550.

Any pointers appreciated.

bimbleuk · 2 Sep 2019 at 10:52

Max 2GB per slot so you'll need 4 x 2GB to achieve the max 8GB.

Scania · 2 Sep 2019 at 11:55

bimbleuk said:
Max 2GB per slot so you'll need 4 x 2GB to achieve the max 8GB.

I’d read something about that whilst trying to troubleshoot this, if that’s the case then why does one 4Gb stick work fine given this limit of 2Gb per slot? and as I say it’ll work individually in any slot quite happily.

Besty · 2 Sep 2019 at 14:28

Scania said:
I’d read something about that whilst trying to troubleshoot this, if that’s the case then why does one 4Gb stick work fine given this limit of 2Gb per slot? and as I say it’ll work individually in any slot quite happily.

should explain why in a little more detail in the manual, short version is that one stick will work fine as it will be allowed to consume the whole 4GB allocation from that memory channel. two 4Gb channels=8GB maximum in four slots.

almost ten years since i bumped into this type of problem so best to crack open the memory compatibility list for that board.

bimbleuk · 2 Sep 2019 at 15:06

Scania said:
I’d read something about that whilst trying to troubleshoot this, if that’s the case then why does one 4Gb stick work fine given this limit of 2Gb per slot? and as I say it’ll work individually in any slot quite happily.

You're right it sounds like the 2 x 4GB sticks should work one in each channel but there must be some quirk that limits the maximum addressable memory per slot when going over 4GB. I did only have a quick glance in the manual at the memory config table that shows the slot combinations.

Memory interleaving or the number of banks per physical RAM stick can have an affect. You'll notice some RAM sticks are single or double sided.