OK, so I received and installed the 2 x 1GB Kingston ValueRAM PC2-6400 modules. No problems.
But what disappoints and befuddles me is that, of the SPD instructions reported by the BIOS it is not selecting the 400MHz (Bus Clock) instruction.
For both modules, CPU-Z gives the reported SPD as:
JEDEC#1 400MHz 6-6-6-18 (tRC 24) 1.8V
JEDEC#2 333MHz 5-5-5-15 (tRC 20) 1.8V
JEDEC#3 266MHz 4-4-4-12 (tRC 16) 1.8V
But the BIOS has selected the lowest 266MHz speed, the same as it also did on the 2 x 512MB PC2-4200 cards that I just took out.
Now, from what I learned about P4 and DDR2 interactions, I understand why the BIOS would favor 266MHz over 333MHz, but why would 400MHz not be selected given that it is faster and matched to the CPU FSB? Does this mean then that CAS timings take priority?
If that is the case, what is to be gained in using PC2-6400 on the Dimension 3100 unless the BIOS allows the SDRAM clock frequency to be manually set, which, as far as I can make out, is not an option. Yet PC2-6400 is what the Dell support page gives as the recommended memory upgrade.
I wondered if there has maybe been a BIOS update that explains this?
The BIOS on my 3100 is version A03 (10/08/2005), which is what it came with. I see on the Dell site there is one available BIOS update to vA04. The stated change-log is ‘Add support for new CPU’, nothing about PC2-6400 support.
So am I missing something here?
If it has any bearing, the CPU and MB versions in my 3100 are:
CPU: Pentium 4 630 3GHz (Prescott) - which BIOS v A03 added support for.
MainBoard:
Dell OJC474
Chipset: Intel i915P/i915G Rev B1
Southbridge: Intel 82801FB (ICH6) Rev04