Upgrading - this one or that one?

[julianhj]

I've got a 4 year old self-build machine (built with the assistance of techy mates)

I spent an eyewatering £255 on '1Gb Corsair Value Select DDR2, 533 MHz, 128Mx64, non-ECC, 240 DIMM' back then.

I realise that for about a tenth of that I can get a further 2GB RAM - my question is which type:

http://www.overclockers.co.uk/productlist.php?groupid=701&catid=8&subid=697

That page shows the 2x1GB Corsair Value Select which is (I think) two lots of what I have. I have an Abit AA8 3rd Eye mobo and P4 3.2Ghz CPU.

Can I stick slightly better RAM, if so what's the best spec, and will it be compatible with my original 1GB?
What is the difference between CAS 5-5-5-15 and CAS 4-4-4-12, and are the two able to run together?
Will buying two extra bits of RAM throw things out of sync if my original RAM occupies only one of the four available slots?

Thanks!

 

[Meronem]

any of the dimms on that page will work, they have slightly different timings but as long as your not benching or running Super Pi for world breaking results it won't matter.

If you were to buy any on that page with slight faster timings than your current ram, the new ram will run at the slower speed. But, the main thing is its all pc4200 / 533

 

[hp7909]

RAM speed is backwards compatible, so you can go for any. Recommend some PC2-6400/DDR2-800 sticks. Might be even handy if you ever choose to upgrade mobo.

 

[Glaucus]

for £55 you could get 4GB of 6400 and just bin your old stick.