4. Memory

Memory is where the information from active programs is kept, so that it can be readily available for the processor. Choosing the correct type of memory for your computer is essential, as slow memory will create a definite bottleneck on your system.

What kind of memory do you need

I see this question asked all the time in forums and usually answered incorrectly. Things here arent as confusing as they may appear. Observe:

  • CPU FSB Speed / 4 = Mainboard Clock Speed
  • RAM Speed / 2 = Memory Clock Speed

Obviously for a stable system you want the two clock speeds to match. Let me get into some specifics to aid the curious mind. The difference above arises because processors use Quad Data Rate Technology (Clock x 4) while the memory uses Dual Data Rate (Clock x 2). Most motherboards run the CPU and RAM synchronously, which means they are run at the same clock speed. Thus a CPU that runs on a 1333 MHz FSB (like the Wolfdale 45nm Core2Duo E8400 3.0GHz that I like) has a motherboard clock speed of 1333/4 = 333 MHz. Therefore I need memory that is rated at 333 x 2 = 666MHz, which would be DDR2 667.

So you do not need DDR21333 memory to run this processor at all! This is a common misconception that leads to a lot of wasted dollars. Most people will of course go with a nice pair of 2x1GB DDR2-800 RAM just to relax the memory a bit while running this CPU and to offer some overhead for overclocking. But how much overclocking does this allow me exactly?

This processor runs at 3000MHz with 333MHz clock speed. Thus the multiplier (which we’ll assume is locked) is:

3000 / 333 = 9

Now if I overclock the processor by changing the FSB, I can safely take the DDR2-800 memory up to:

800 / 2 = 400 MHz

I can take the processor up to:

400 x 9 = 3600 MHz

This specific CPU can handle that with the stock cooler. Note also that most memory can be pushed around just like any CPU can and you ‘ll find that DDR2-800 memory, clocked at 400 MHz will sometimes get up to 450MHz depending on the quality of the electronics and luck.

Study the above calculations carefully and you will unlock the secret to choosing your memory and overclocking your system at the same time. I will go into this in detail in the overclocking section.

Reading reviews of specific memory sticks is necessary if you’re planning an ultimate computer. If not, then any current CPU will run wonders on some nice DDR2-800 memory that is getting cheaper and cheaper by the minute.

I have only spoken about DDR2 memory here, because I kept the DDR2 Vs DDR3 comparison for the following section. Its interesting and a good thing to know so read on.

DDR2 Vs DDR3

Lets get this out of the way, since the evidence is clear.

There is no contest (yet). DDR3 can only beat low latency DDR2 at high clock speeds. You may end up spending double or triple the money that you’d have to fork out for DDR2, and the performance difference most likely is close to zero. Read the definitive shootout that Tom wrote up for us:

Toms Hardware: DDR3-1333 Speed and Latency Shootout

A good quality DDR2 FSB800 memory that runs at 200MHz can often be pushed beyond its limits, which is good for overclocking without having to go to the more expensive FSB1033. Heat spreaders should always be used as a precaution, especially in OC projects and especially since they only cost about $5.

ECC and Memory Timings

ECC is a new feature that is built into most new motherboards and memory sticks that allows the memory to pass its timing information to the motherboard. This alieviates the trouble of newbies overclocking/maximizing the effectiveness of their memory, but doesnt really matter much to those with some adventure in them.

Memory timings is something that may have caught your attention. They are the string of numbers that look like 5-5-5-15. These are the percharge, charge, unchargea and ready-ing times that the memory needs to process information. In english, they signify how fast a stick of memory can process information. Memory optimization usually invonves decreasing the timings from the motherboard until the computer is unstable. Then you go and increase the memory voltage a little bit and try it again. If you push the voltage too high, the memory fries, so you gotta have a gentle touch.

A successful overclock usually leaves the memory in a 4-4-4-12 state, with a little bit of voltage added. People almost never go further than that, as the improvements are very small. At this stage your machine probably just picked up a 5% performance boost. In terms of a game’s fps this means that from 30=>31.5 fps just from the memory.

Some of this information relates clearly to overclocking, but I state it here because several vendors quote the max timings that their memory supports. Using ECC, the motherboard should pick up the fast, usually 4-4-4-12 timings without any messing around at all from your part, so this is something to look out for.

Memory Speed and FSB Speed

The system memory has to be able to keep up with the processor FSB. Some motherboards allow the CPU and memory FSBs to be tweaked independently, but this is a custom feature that ony some BIOS allow and only becomes important for overclocking. I have added this section seperately so that I can specifically answer a few key questions that I see often in forums and review sites:

The first is “if the CPU is unlocked, is it better to pick faster FSB or higher clock speeds?” : The simple answer is that it doesnt make a difference. Whatever gets you the highest CPU speed overall is the option you should go with. That said some applications/games have gain advantages with a high FSB but not enough to warrant the cost of expensive memory and motherboard.

This is a good time to start looking through the futuremark benchmark results. You will see how the FSB ratings vary. CPU speed and FSB speed doesnt seem to correlate well enough for us to say “high FSB is good”. You may have a different opinion, so please head over to FutureMark’s new realtime benchmark submission page and have a look at some systems and specs:

Futuremark Benchmark Ticker

In some cases, and while overclocking you will find that further OC requires faster memory, which generally speaking will not be readily available by the user, just for overclocking purposes. Thus careful planning is necesary and intimate knowledge of the abilities of the motherboard, cpu and memory. What Im trying to say is, if you are planning on overclocking, you should read some reviews and figure out exactly how much far you are going to go and make sure that the memory you buy can handle it.

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So what good quality memory modules are there? This is what I’ve found:

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