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How to Install SDRAM Memory Into a PC (Page 2/5)

Written By: Dan "Tweak Monkey" Kennedy
Posted: July 10, 2001

Memory Speed

(For the purposes of this article I'm going to assume you already know what a MB is, and I am going to assume that you know the MB of RAM you have, the better. And I'm also going to assume you know that there is a point where more RAM doesn't help. In Windows 98 systems this is usually around 128 MB, and for most users (gamers?) with Windows 2000, this is around 256 MB)

When purchasing memory, you'll likely find a plethora of terms with each product. One of the more obvious is the speed rating. Let's assume you go to buy RAM and find the following:
128 MB PC100 - $64
128 MB PC133 - $69
128 MB PC150 - $79

If you buy the more expensive RAM, are you getting a faster memory stick? Will the memory last longer? Will your PC be faster? No, not necessarily. Almost every component in your PC operates at a certain frequency, or speed, which is determined by the bus speed set on the motherboard. For early Pentium II systems, this was 66 MHz. For later Pentium II and some Pentium III systems, this was 100 MHz. For later Pentium III systems, this could be 133 MHz. Now these are just the default, recommended settings. Overclocking a system bus could increase these considerably.

Some brands are better than others, but most work fine.

So how does PC100 memory differ from PC133 memory? PC100 memory is essentially "stable" on 100 MHz bus speeds and below. That isn't to say it won't work at 133 MHz and beyond, but it will probably lead to some problems, such as system crashes. PC133 is good for up to 133 MHz bus speeds (by spec). Again, it could reach 150 MHz, but if you're going to use a higher bus speed you might as well buy the higher spec'd memory. To find out which bus speed your system uses, read the manual or ask a friend. It's just easier that way. :)

If you plan to overclock your system, buy RAM that can accomodate a higher bus speed. Don't buy PC100 just because it's $5 less than PC133. Just buy the PC133. If you're 100% sure your system will remain at 100 MHz bus speed for the entire life of the system, still consider buying faster RAM! You may upgrade the system some day to a 133 MHz bus speed system, and if that's the case you could always re-use the RAM. I think that's enough on memory speed.

CAS Latency

I'm sure you've seen memory that says "CAS2" and "CAS3", but you might have no idea what the differences are between the two. I should mention that if your memory doesn't have a specified "CAS" setting listed, it is probably CAS3. CAS3 is cheaper to produce and for the most part, easier to sell. CAS2 is for high-performance applications. What does it all mean?

If your system has CAS2 memory and it is enabled in the BIOS setup, you'll have a very nice speed increase when doing input/output through the RAM. Any program you run uses the system RAM, so in essence, every program is faster. The speed notice may not be visible to the human eye, but it's definitely there. RAM is already so fast compared to a hard drive that when things are loaded from RAM, they seem almost instant. CAS2 makes that instant into 2/3 of an instant. It is significantly faster than CAS3, but you probably won't notice the difference in real-world applications. Also, note that higher bus speeds benefit more from CAS2 than lower bus speeds. The difference between CAS2 and CAS3 may not be as obvious at 100 MHz FSB than it is at 133 MHz FSB and beyond.

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