Can a PC Support Different Size RAM Sticks?

Reader Jade writes: I have a Dell 2350 and want to upgrade my memory. It now has 256MB of PC2100 (266MHz) DDR SDRAM (non-ECC), with a capacity of 1GB. Nowhere in my manual can I find if I can mix the sizes of memory sticks, and I read somewhere that some computers you can not mix the sizes. I was wondering if I could use a 256MB and a 512MB stick. Or if I have to use two 256MB, as two 512MB sticks would go over my capacity. Thank You!

Excellent question, Jade. Long ago, computers did indeed require identical RAM sticks (called DIMMs), often in groups of two. But those days have largely passed, and most computers now can support any combination of DIMMs, in various sizes and even different speeds.

For your machine, yes, you can remove one of the 256MB DIMMs and replace it with a 512MB DIMM. It's recommended that you use PC2100 RAM, and make sure it is also non-ECC (non-error correcting), as ECC RAM will not work in the machine. Fortunately for you, PC2100 non-ECC RAM is still a common type of memory on sale today, and 512MB should cost you less than $50. You can probably also use faster RAM (indicated by a larger number, like PC2400 or PC2700), but the RAM will run at the lower PC2100 speed due to the DIMM already in your machine, so there's no reason to spend extra on the faster stuff. You won't notice a difference, anyway. Always, however, buy brand-name memory from Kingston, Crucial, Micron, Samsung, or another big brand. Generic memory can be unreliable and lead to crashes.

Now, not every computer lets you install RAM willy-nilly like this. Systems that use RDRAM (which you don't see much any more, but which were popular three or four years ago) required identical memory sticks to be installed in pairs (or four at a time). RDRAM is still frightfully expensive and performance is no better than SDRAM, but there's no way to switch from RDRAM to SDRAM without jumping to a new computer.

In answer to your final question, 512MB x 2 = 1GB, actually, as a gigabyte isn't 1000MB but rather 1024 of them. So you're free to upgrade both DIMMs to 512MB if you want the extra RAM headroom.