I currently have 256 MB of PC100 SDRAM, and wish to upgrade this, now i dont know the difference and compatabilities of the different types of RAM... Do i have to buy another 256 of PC100 SDRAM or can i use DDR? (i.e can i mix the two types?) Will my motherboard be compatable with DDR if i decide to just use that? What are the differences between these types of RAm and what else should i look out for? Thanks guys

If you already have 256MB of PC100 then you need to use a PC100. It can be 64MB or 128MB as well not just 256MB. DDR RAM will not work with your board if it doesn't have DDR slots. DDR requires different physical slots. it has 184 pins where the PC100 has 168 pins. DDR stands for double data rate and it takes a motherboard designed for it. You might be able to use PC133 but you would need to remove the PC100. putting the two together could cause conflicts and you would have more trouble than you already have.

See www.crucial.com they might give you more info.....

Correction Rick, putting PC133 and PC100 will still run but both of them run ah 100Mhz, I tried. About the DDR part, you have to check your motherboard maunfactory, i believe there are ONLY A FEW motherboards that support DDR and SDRAM, you can only use either DDR or SDRAM. CAN'T NOT BE MIX. ~Death-Knight~

Yes, the mixing RAM of SDRAM will run at the slower speed.

Yes you are right about being able to mix PC100 and PC133 at the lower speed. however some cannot. I have seen conflicts occasionally and some Memory manufacturers don't recommend it because of the possibility of conflicts. sometimes it's better to be safe. I've added PC133 to a PC100 and it actually slowed the system down and recieved the fatal exception error. usually it can work though