Reader Chris writes: When choosing RAM is it better to get two  512MB sticks or one 1GB stick in order to get one gig? Also, is it better to choose a higher frequency when the PC requires, say, 533MHz PC4200 DDR2 SDRAM?

It's true: Two smaller RAM sticks will perform better than one larger stick. Why? Because the PC can access both sticks in parallel, so your computer can (theoretically) have access to twice the RAMage as it could if you had only the single RAM stick. 

Back in the old days when I used to test and review enormous file servers, I'd see vendors use every possible RAM slot in order to take advantage of this effect. It wasn't uncommon to see a server with eight RAM sockets, each featuring a 128MB RAM chip, for a total of 1GB of RAM.

Realistically, if you aren't running a web server off your computer or dealing with some application where every ounce of computing power counts, you aren't going to notice much of a difference with, say, a 2x512MB vs. a 1x1GB RAM configuration. Personally, I tend to buy the largest RAM sticks I can afford when I'm upgrading a machine. Since most PCs have two slots, a typical scenario is finding a PC with one 256MB stick already in place, and I'll just add a 1GB stick to that to upgrade the RAM to 1.25GB, rather than remove the 256MB stick and replace it with two 512MB sticks. If I'm configuring a new PC, I usually just go with what's cheapest, and a single 1GB stick will be about 10 to 15 percent cheaper than two 512MB sticks.

Whew!

As for your other question about RAM speeds, there's no point in buying RAM that's faster than what the PC calls for. Why? Because the memory bus on your computer runs at a certain speed, and even if your RAM can run faster, it won't, because the PC won't feed it data at that speed. Bottom line: Just buy exactly the RAM speed that your PC requires, and only get faster RAM if the lower-speed RAM has been discontinued. Otherwise you'll just be wasting money.