Hi 02GF74, What your best doing, is going to www.crucial.com and running their scanner for your memory. As for the 32bit version, if you have 4GB of memory the 32bit will only see 3.25GB, where the 64bit will see it all.

thanks for that;  I checked, and as expected, am runnng Vista 32 bit. so now need to decide if I want to fit another 2 GB, of which almost 40 % will not be usalbe of slip in a cheaper 1 GB module.

I have been looking on ebay for memory and am abit confused by the types.

What crucial and other sites recommend is DDR2 PC2 6400

but what I have installed is 2RX8 PC2 6400S  (hynix brand)

I have seen 2RX16 and 1RX8

So my question naturally leads on to what is the difference between DDR2, 2RX8, 2RX16 and 1RX8?

I am guessing DDR is the top of the pile so I suppose I should replace the 2GB of 2RX8  I have now with 2 G DDR for best performance?

a bit of googling brought up this

now I need to figure out what it all means ..... so I can work out what to fit.....