DDR2 RAM Upgrade

**montecarlo** · April 6th, 2008, 12:54 PM

I have a Dell Inspiron 6000 Laptop. As of now, it holds 512 MB (2 * 256 MB) DDR2 -533 (PC2-4200) RAM. I would like to upgrade it to 2 * 1GB. For this I checked out the Crucial Tool, which suggested that I use PC2-4200 itself. However, PC2-5300 (DDR2 - 667) was also listed as a compatible upgrade. The prices of both are the same. Also I noticed that the CAS Latency of 5300 was 5 and that of 4200 was 4. Further, I ran CPU-Z on my system and it reported that the FSB was 400 MHz (Bus Speed 100 - Quad Pumped). The CPU speed was alternating between 600 MHz and 1.6 GHz (The Multiplier was alternating between 6 and 16).
My question is this: Which is the better option? Should I choose PC2-4200 or PC2-5300?
Thanks.

**Platypus** · April 6th, 2008, 09:23 PM

The PC2-5300 will be backwards compatible, as it will run at the lower clock speed. However as you've noted, the faster memory typically has higher latency (slightly longer between access cycles). So unless you want to allow for possibly using the memory in a future faster machine, I'd suggest staying with the PC2-4200.

**montecarlo** · April 7th, 2008, 12:08 AM

Thanks Platypus.
What is the frequency that the RAM will actually run at? I mean, for a particular motherboard configuration, how do you find the optimal RAM speed to be used? I am slightly confused about that. Please clarify.

**Platypus** · April 7th, 2008, 07:24 AM

It looks like your machine would have an M725 CPU, and for M7x5 series processors, Dell's specification was PC2-3200 memory (the existing RAM is probably this lower specification). The clock speed is tied to the CPU bus speed, unless the BIOS has the capacity to run memory asynchronously. So even the PC2-4200 would be over specification for a 400MHz bus CPU, and would run at the correspondingly lower speed. There are 6000 series machines with M7x0 series CPUs (533MHz bus speed) so the PC2-4200 recommendation covers those units as well.