I have a 5 yr old desktop with a P4 2.66GHz. The board is D915GLVG with 4 DDR slots of 1Gb max capacity each.
I have filled all the DIMM slots as follows:
1) 2 x 1024Mb in 2 slots
2) 2 x 256Mb in the other two slots
All the memory modules are 400MHz. 3 sticks are from the same vendor, say A, ie 2 x 1024Mb and a 256Mb. The 256Mb one is single sided while the 1024Mbs are double sided. When the ones from vendor A are used, the bios correctly shows system memory speed as 400MHz.
The 256Mb from the other vendor, say B, is double sided. If the vendor B's 256Mb is used alone then too the bios shows 400MHz. But when A and B are used together in any combination the bios shows 333MHz only as system memory speed.
The total installed capacity is correctly shown in the bios, just the speed is 333MHz instead of 400MHz. Any idea why? The OS is correctly functioning.
Also the processor is capable of handling only 333MHz.
That is normal for your board. Many older p4 boards ran slower with all ram slots filled.
I have access to another desktop with the same board ie D915GLVG, but the processor is P4 3.00GHz (this processor can fully use 400MHz DDR ram).
This board has 2 X 1024Mb and 2 x 512Mb correctly fitted on the slots in the interleaved mode. The RAMS are from 2 different vendors. Yet here the bios correctly shows the system memory speed as 400MHz.
In both cases for same board model all 4 DIMM slots are correctly filled, yet one shows 400MHz while shows 333MHz. So what do you say mate?