Hi there, just wondering if anyone knows if it's possible to use DDR2 PC2-4200 in a computer that currently has DDR2 PC2-5300 installed? Are these 2 compatable? Cheers!

If you pair up PC2-4200 (DDR2-533) with PC2-5300 (DDR2-667), ALL the RAM will run as PC2-4200. In other words, you'll end up with more total RAM but it will be running at a slower speed. Which CPU do you have? "If my answers frighten you then you should cease asking scary questions" - Jules Winnfield (Samuel L. Jackson) in Pulp Fiction

My processor is AMD Athlon(tm) 64 X 2 Dual Core Processor 5400+ Max space in the PC RAM is for 8GB. If 4gb of this was PC2-4200 and 4gb was PC2-5300, it would all run as PC2-4200 then? WWhat would be faster? 8GB 4200 or 4gb 5300 Thanks!

If you're running the 32-bit version of XP, 4GB is the max, but it will be recognized as less. It could be 3.5GB, 3.25GB, 3.0GB or even less...it depends on the hardware you have installed. Regardless of that, the proper RAM to run with an A64 X2 is PC2-6400 (DDR-800). PC2-5300 will bottleneck the system slightly, PC2-4200 will bottleneck it even more. "If my answers frighten you then you should cease asking scary questions" - Jules Winnfield (Samuel L. Jackson) in Pulp Fiction

And more RAM does not automatically speed up the machine. If you have enough RAM to run your normal workload adding more does not help. You can determine how much RAM you are using, and if the Page File is being overly used, in the Task Manager/Performance window. Checking memory usage: http://www.whiz-tech.com/guides/ram...

Yup - i'm aware that more RAM doesnt speed up a computer but rather allows you to have more programs running simultaneously. This is what im after. I run photoshop, itunes, smartboard software and other processor hungry software, and often sit around waiting for things to happen. Perhaps the word 'faster' was misleading. I figured people would know what I was getting at... So at the moment, I am under the understanding that XP pro 32 bit is limited to 4gb, and that putting 4200 in will cause the 5300 also run at 4200. This will bottleneck the PC somewhat. I was thinking I'd put my 2gb of 4200 and 2gb of 5300 in the pc, until I can replace it with 4gb of 5300. I assume 4gb at 4200 is better than 2gb at 5300?

"I assume 4gb at 4200 is better than 2gb at 5300? Not necessarily. Like I said earlier, it depends. If 2gb does the job without using the Page File excessively, then the 4gb running slower will slow you down. I suggest that you do some testing.