How to build a computer
How To Build A PC - A Computer Building Guide
Rob Williams - contact via the forums
Last Updated: 1/3/2016
How to build a computer
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Build A Computer Like My Super PC

RAM - Computer System Memory

RAM (Random Access Memory) is the main system memory of the computer. A total of 1024MB of RAM (1GB of RAM) is sufficient in many cases to ensure the overall system performance is not unduly impaired by the amount of RAM in the system, but a general purpose computer of today should have 2048MB of RAM (2GB of RAM) or more.
How to build a computer - Crucial Ballistix 1GB PC3-12800 DDR3 memory module Click on the picture to see it enlarged.

Not all computer system memory is the same. For example, DIMM memory modules have been the common form factor years, but they come in a variety of types, including DDR, DDR2, DDR3 and DDR4. The type commonly with motherboards today is DDR3. Even among compatible memory module type, there are a number of manufacturer's from which to choose. It's not only important to purchase RAM that's compatible with your computer, it's important to choose top quality RAM. Many computer problems are due to the use of sub-quality RAM. Companies such as Kingston and Corsair have good reputations, and Mushkin makes the highest quality RAM for those willing to pay a premium price, but for top quality RAM without paying extra the place to go is Crucial.

Crucial memory comes with a lifetime guarantee and shipping is free. And they take the uncertainty out of compatibility and of knowing which RAM is right for your computer with their handy advisor. Start by selecting your motherboard (such as ABit, ASUS, EPoX, MSI, etc.), clicking Go and then follow the selections to find the RAM compatible for your motherboard. The page listing the compatible memory modules will also show the maximum amount of memory your particular brand and model of motherboard supports.

U.S. and North American Systems UK and European Systems
Memory upgrades from Crucial Technology - Computer memory, flash and video card upgrades
The Crucial Memory Advisor™

Select your system and press go!

Memory Upgrades from Crucial Technology
The Crucial Memory Advisor™

Select your system and press go!


As you might guess, each type of DDR memory provides greater performance potential, starting with DDR, then DDR2, then DDR3, and so on. DDR3 memory modules and higher are more commonly used in add-on cards, especially video cards.

DDR2 memory modules run at faster speeds than DDR, including effective speeds of 400MHz, 533MHz, 667MHz, 800MHz, 1000MHz and 1067MHz. But DDR2 memory has a higher latency, meaning it takes more clock cycles to deliver the data. This higher latency actually causes DDR2 memory to be slower than DDR memory, even when running at higher MHz speeds. As a general rule, DDR2 memory of 800MHz or higher must be used to equal or exceed the performance of DDR 400MHz memory. But DDR2 has a great deal of upward potential in performance, whereas DDR memory tops out at 400MHz. And although they physically don't look very different, they have significant differences in terms of voltage requirements and architecture.

For a great deal more information regarding memory and for detailed, step-by-step instructions on how to install memory, check out my Computer Memory Upgrade - How To Add Or Upgrade System Memory (RAM) For Your Computer site. If you're wondering about such things as unbuffered memory, buffered memory, registered memory, parity, non-parity, ECC, or anything else about memory then this site will help!

I'm often asked if it's better in terms of performance to get one memory module or two memory modules. For example, is it better to get one memory module of 512MB or two memory modules of 256MB? With DDR memory like I use in My Super PC, there is a slight performance improvement using two memory modules instead of one memory module. My own measurements comparing two 256MB memory modules to one 512MB memory module that are identical except for size show a two percent to three percent improvement in performance using the two 256MB memory modules. Running pairs of identical memory like this is called "Dual Channel", and it is recognized automatically by the motherboard.

DDR2 RAM Timings, Latencies Speeds And Performance

I tried a number of different Crucial memory modules using the same computer hardware configuration to see for myself what peformance differences there would be. I ran two different tests, one being the Half-Life 2 benchmark and the other being the Futuremark 3DMark05 benchmark. This is by no means a comprehensive set of tests, but it should give a reasonable indication of what to expect. Both tests are graphics intensive and will give the system RAM a good workout. Both tests make good overall system performance tests. The Half-Life 2 Benchmark and PCMark05 benchmarks are run as described on this page, with results given in fps (frames per second). I describe the Futuremark 3DMark05 Benchmark on this page.

All the memory modules I used were 1GB in size, unbuffered and Non-ECC. The rest of the hardware in the computer - processor, motherboard, video card - were identical for each test. I used both standard RAM memory modules and high-end, performance RAM memory modules, identified as Ballistix by Crucial.

Computer Memory Speed Tests With 1GB of RAM

Each test was done with a single, 1GB memory module. As you can see, performance improves with each faster memory module. The Half-Life2 Benchmark appears to be particularly sensive to RAM performance. A 3DMark05 score can vary by as much as about 100 points on successive runs on the same hardware, so scores within that range of each other are not significantly different.

Memory SpeedTimingsHalf-Life 2
PC2-4200 DDR2-533 CL=4 35.3 fps 6278 13330
PC2-5300 DDR2-667 CL=5 36.8 fps 6418 13754
PC2-6400 DDR2-800 CL=5 47.3 fps 6468 13921
Ballistix PC2-6400 DDR2-800 4-4-4-12 51.0 fps 6504 13977
Ballistix PC2-8500 DDR2-1066 5-5-5-15 51.8 fps 6454 14060

Computer Memory Speed Tests With 2GB of RAM

Here are the results from running the same tests with 2GB of RAM. The first entry is standard, non-performance RAM, that is not even of the same type so it does not even get the small advantage of performance in dual channel mode. Still very good RAM of very good quality, but not high-end RAM. The next two entries are different speeds of high-end RAM. As you can see, the high-end RAM yielded much better performance, something like 25 percent better. Still, the standard RAM would be sufficient for many users.

It's really interesting that the performance of the two different types of high-end RAM is nearly identical. Although the DDR2-1066 RAM has a higher speed, the DDR2-800 has lower latencies due to faster timings. As a result, the two finish up about the same.

One thing that is clear is that the quanity of RAM, 2GB instead of 1GB, can make a big difference, regardless of the type of the smaller quantity of memory.

Each test was done with two, 1GB memory modules.

Memory SpeedTimingsHalf-Life 2
PC2-4200 DDR2-533
PC2-5300 DDR2-667
82.9 fps 6318 13280
Ballistix PC2-6400 DDR2-800 4-4-4-12 104.4 fps 6509 14282
Ballistix PC2-8500 DDR2-1066 5-5-5-15 107.5 fps 6488 14280

How Much Computer Memory Is Enough RAM

The tests emphasize what most experienced PC builders know. Generally speaking a computer needs 1GB of RAM as a reasonable minimum. A reasonable maximum is 2GB of RAM. It is often the quantity of system memory that makes a big difference in overall system performance, rather than the actual speed of the system memory. However, since RAM is one of the bigger bottlenecks in system performance, it may well be worthwhile to use RAM with a faster speed as well.

Both Windows XP and Windows Vista will perform better with at least 1GB of RAM, and 2GB is a better rule-of-thumb. If you're using a 32-bit version of the Windows operating system, such as Windows XP or Windows Vista - and most of us are - then be aware that the maximum amount of system memory actually available to the user is between 2.75GB and 3.5GB, as I explain on this page regarding Windows problems recognizing 4GB of RAM. If you are using Windows 98SE and are looking to go above 512MB of RAM then you should be aware of this Microsoft Product Support Service article which documents this problem and my own Fix For "Out Of Memory" Error On Windows 98/ME Systems After Adding Memory page, which shows how to fix the problem.

It's perfectly reasonable for many computers to have even more than 2GB of RAM, depending on the type of applications being used, and especially if the computer is running a number of applications simultaneously. Computers built with playing PC games as an important consideration should definitely use as much memory as their computer will hold.

I have the physical maximum amount supported by the motherboard in My Super PC, for a total of 4GB. As it turns out, the usable amount of memory available to applications is 3.25GB, as can be seen on this page. If you really want to be sure that you have your computer configured with all of the RAM it can use then it needs to have at least 4GB of RAM physically installed. This is because the usable limit varies, depending on the computer hardware and configuration. As I mentioned before, it's somewhere in the range of 2.75GB to 3.5GB. And with prices of RAM so low, it's tempting to go ahead and max out the computer memory.

Next: Build A Computer Like My Super PC - Video Card

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