1.25GB ram detected, but i have 1.5GB??

okay..system

AMD Athlon XP 2800+ oc mild to 2300MHz
1.5GB (3x512MB) DDR333
ATI Radeon x1650xt 512MB AGP OC
AOpen ak77-600MAX mobo
2x 400GB SATA drives
Audigy 2 zs P

problem:
i have 1.5GB of ram. Motherboard supports 3GB, 1GB per slot. Windows says i have 1.25GB. so does 3dmark. CPU-Z says i have 1.5GB. BIOS says i have ~1.31GB. why does my extra 256MB not register? i have latest bios, v1.09. i don't get it...did i miss some setting in the bios? please just tell me its some silly thing i overlooked.
 

lewbaseball07

Distinguished
May 25, 2006
783
0
18,990
tell you the truth i dont freaking use it i just like saying i have linux,xp, and vista on my computer lol

when i get a hold of an extra hdd ill install osx but......


sooo to your prob......ahh....

so u tested all three 512mb sticks altogether in another rig? or indiviually tested?
 

rammedstein

Distinguished
Jun 5, 2006
1,071
0
19,280
this may sound stupid but have you disabled you integrated graphics if your mobo has it, sometimes even after sticking in a agp/pcie card it stays turned on
 

aztech

Distinguished
Apr 13, 2004
114
0
18,680
well that mother board doesnt seem to have onboard video. but if your ATI Radeon x1650xt 512MB AGP OC has turbo cache thats what is using your system memory.
 

darkstar782

Distinguished
Dec 24, 2005
1,375
0
19,280
Motherboard is using a VIA KT600 chipset with a single channel DDR1 memory controller.

3 DIMMs will be unstable at DDR400 speeds. You need to run at DDR333 MAX.

Motherboard will not support 3 Double sided DIMMs either. You probably have 2 double bank and 1 single bank 512mb DIMMs there, and are loosing half of one of the 512MB DIMMs.

In short, if you want more RAM you need either 2*1GB DIMMs or a new system
 

darkstar782

Distinguished
Dec 24, 2005
1,375
0
19,280
Known and used many Athlon XP systems over the years, and never liked the nForce chipsets or saw the point in dual channel with a max FSB of 400MHz, so I have used many many KT333, KT400, KT600, and KT880 motherboards ;)

To be honest I usually stick to 2 DIMMs in them, as you have discovered 3 DIMMs is usually a hassle, either because of speed limitations or because of bank limitations.

The KT600 memory controller was only ever designed for 2 DIMMs on a single channel, hence supporting 4 banks. Motherboard makers put 3 slots on most of the boards to try to narrow the gap with the nForce 2 Ultra boards that had 4 slots / Dual channel.


EDIT:
Just re-read your original post, you say 1.31GB? This is very different from 1.25GB :p
If it is the bank issue, you will see exactly 1280MB in BIOS or windows. Unless you are seeing 1,310,720KB? (which is 1280MB...)