Random Access memory (RAM) is the main memory of a PC where every thing is loaded before it can be processed. Everybody knows there are lots of processes running in the background than it appears. Applications nowadays are resource hungry, they demand like anything. So, your 1yr old PC will not win the battle with stone age tools. Either you upgrade core components or buy a new one. Buying a new PC is not feasible every time, so considerable performance gain can be achieved by addition of more RAM on every PC whose other components are not bottlenecking the system. (I mean don't expect a blazing fast computer if you have upgraded to 512MB RAM with a Celeron)
Type & Clock of RAM : First of all you need to know what type of RAM (SD, DDR, DDR2) your motherboard supports. Now it is time for you to decide how fast RAM you want and how fast your motherboard can support. Yes, I am talking of the bandwidth they can offer. You might have seen RAM sticks as DDR 333Mhz, DDR 400Mhz, DDR2 533Mhz etc. This clock (mhz) is your bandwidth factor. The more, the better. To know either look at the manual provided with your motherboard or do a little search on google with your motherboard model number. Now you are ready with what type and mhz of RAM you want.
Two things still left for consideration are the latency & dual channel.
Latency is the time delay only after which the data can be accessed in the RAM. So the less,the better. No need to go into the details of latency because low latency rams are 30% to 100% more costlier than high latency RAM. So you need not consider such details while buying RAM for your desktop PC. Just go for branded names like Kingston. They tend to perform better than others. If you tend to go deeper in the latency stuff, I recommend this link.
Dual Channel is like you are running two identical sticks in combined mode, doubling the data transfer rate. This feature needs to be supported by the motherboard. Just insert two identical sticks in same colored module and its done. If you want good performance, go for matched pairs that specially come in a single packaging specially for dual channel performance. They are little expensive from normal RAM sticks but worth it.
- When running two sticks, the whole system will run at the lower clock out of the two supported. For example : 1 DDR2 533Mhz and 1 DDR2 667Mhz will run @ 533mhz if run together. i.e. One will underclock itself
- Never try any incompatible stick in your motherboard. Although they might run well in some case but they can also smoke up your cabinet. For example: If your motherboard supports DDR2 upto 667mhz, don't try the 800mhz stick. Even if it runs then also it will underclock itself to 667mhz. So it will cost more and will give no performance gain. (Don't go with the vendor)
- Buying RAM running greater than FSB is pointless. FSB is how fast data can be transferred between processor and RAM. There is no point of buying a 667mhz stick if your processor has a FSB of 533Mhz.
I hope you will learn something from this. Any queries, suggestions and comments are welcome. Do tell me how you like the article.