DDR2 667Mhz CLass 5 vs CL6

Whatever the Default RAM Frequency is for your CPU then that's the fastest Dell or any OEM BIOS is going to allow. DDR2 800MHz will down-clock to DDR2 667MHz and the lower the CAS per Frequency then the faster the kit -- DO NOT MIX: Frequency, CAS nor especially Voltage. Yes 2GB for XP and 4GB of Windows 7 are the minimums I recommend.

As far as which kit -- flip a coin.

CAS vs Frequency:

CAS is a measure in ns nanoseconds (billionths of a second). The DDR2-800MHz will down-clock to same overal 'speed' as the DDR2-667MHz kit.

The calculation of CAS latency for the Chart above is CAS latency (ns) = (CAS / Frequency (MHz)) × 1000

OK. Thank you both. The chart is very helpful & the info on higher MHz & higher CL is great. Will commit to memory - no pun intended.
Guess will buy the PC2-6400 Kit, it is a couple $$ cheaper.

thanks

I hate to nitpick but the DDR transfer rate is twice the IO bus frequency, not twice the core memory frequency. There's another ratio between the IO Bus frequency and the core memory frequency, for DDR it is 1:1, for DDR2 it is 2:1, and for DDR3 it is 4:1. Thus, DDR-400 / PC-3200, DDR2-800 / PC2-6400 and DDR3-1600 / PC3-12800 all have core memory frequencies of 200Mhz with IO bus speeds of 200Mhz, 400Mhz and 800Mhz respectively. Even top of the line DDR3-3000 only has a core memory clock of 375Mhz

Best answer selected by snoots.

Not to nit pick either, I never said anything to the contrary. Though on Intel the '1:1' doesn't pertain here if the BIOS is limiting the RAM to DDR2-667; the OP's Intel® Core™2 Duo Processor T7250 (2M Cache, 2.00 GHz, 800 MHz FSB) therefore the ratio is 3:5 not 1:1. Further, you're mixing two different things into one: (1) I/O bus clock - is the actual clock speed of the RAM, (2) 1:1 refers to the ratio of the CPU's (rated) FSB : I/O bus clock of the RAM. I've seen this same issue with Dell and other OEM BIOS many times.

OP:

ME:


Looking up the Intel Core 2 Duo T7250 - http://ark.intel.com/products/31728/Intel-Core2-Duo-Pro...(2M-Cache-2_00-GHz-800-MHz-FSB) ; it has a FSB of 800MHz so DDR2-800 will work but Dell is apparently setting (limiting) the RAM to DDR2-667 (3:5).

Dell's Specs "Min: 512MB DDR2 shared 667MHz; Max: 4GB DDR2 shared 667MHz" - http://www.dell.com/downloads/ap/products/latit/LAT_D63...

Example of a Dell:

That's the Front Side Bus, not the memory IO bus. The IO bus clock is not the speed of the ram modules. DDR3 makes 2 transfers per IO clock and there are 4 IO clocks per module clock