Memory

What the heck is a...?
People get the memory and hard drive mixed up all the times. Both are storage mechanisms, but memory is extremely fast temporary storage used by the computer's processor while it's actually doing work, while the hard drive is much slower permanent storage used by the computer to store things long term. Sometimes you'll hear the term "RAM" when talking about computers. This is another name for the computer's memory. RAM stands for "Random Access Memory", named after the way data is retrieved from this kind of storage. Read more about it here, if you're interested. The important thing to understand is that when some computer nerd or sales person uses the term "RAM", they're talking about memory, not the hard drive.

Unlike the hard drive, which keeps programs and data intact even when the power is off, your computer's memory is "volatile". This means that it only works while the machine is turned on. And when I say that memory is tremendously faster, I'm not exaggerating. In the modern PC, data can literally be retrieved by the CPU from memory about 100,000 times faster than it can from the hard drive.

The Filing Cabinet Analogy
Think of the hard drive as a filing cabinet. This is where you keep files for the long term. Now, think of memory as your desk. When you want to work on a file, you take it out of the filing cabinet and put it on your desk to work on it. The computer does the same thing. When it wants to work on some piece of data, it pulls it off the hard drive (comparatively very slow) and puts it on the desk, where it can be accessed easily and quickly.

Now, imagine working on multiple things at one time - something computers are very good at. If you had 10 files you wanted to work on simultaneously, how would you do it? Would you take file #1 out of the file cabinet, work on it for a few minutes on your desk, then return it to the file cabinet, then take out file #4, work, replace, take out #2 and #7, work, replace, and so on? No. You'd get out all ten files, make a stack on your desk, and interchange them quickly without ever leaving your chair.

So does the computer. When it needs to work on ten things at once, it puts them all in memory. And it's actually really smart about trying to predict which things to leave there (because it thinks you'll use them again soon) and which to put back on the hard drive for longer-term storage. Why? Because it takes so long to get things off the hard drive that if it needed to run back there for every piece of data all the time, your computer would slow down to African sloth speeds.

The Moral of the Story
Conclusion... You need a lot of memory. The more things you think you'll do at the same time, the more memory you need. Think about it this way... If your PC doesn't have the space to keep files on its desk, it's going to have to keep them in the file cabinet, and spend all kinds of time running back and forth to get the files that it needs. This would certainly slow you down if you had to work that way, no? The catch is that memory is one of the most expensive parts of the computer. It gets cheaper and faster all the time, but still a pricy component compared to the rest of the box.

How do you measure the size of memory? Remember that this is a space measurement, just like the hard drive, just on a smaller scale. The basic rule is that the hard drive is big and cheep and slow, while memory is small and fast and expensive. Therefore, the hard drive will always be about 50-100x larger than the memory on any computer. Both are measured in bytes. Memory is millions- to billions of bytes, so mega- to gigabytes, abbreviated MB and GB respectively.

Type of Memory
Memory has become a lot more complicated as new technologies have been introduced. This is where an article like this one can get really complicated if we let it. So, here's how we'll play it...

If you're buying an old computer (using SDRAM or older), all memory will be cheap and the max amount your computer can hold will still be less than the 2GB ideal we're shooting for (letting the cat out of the bag early). So the net of it will be to get as much as you can get your hands on, and skip to the next section of the article.

If you're buying a newer computer (using DDR or DDR2), then keep reading so we can sort out a few new technical terms. This newer memory comes in two flavors - DDR and DDR2. The only advantage of DDR2 over DDR (as far as the vast majority of us are concerned) is that DDR2 uses newer technology that allows us to arrive at faster speeds.

So, ask the dealer what kind of memory the system supports. Get DDR2 if possible, and fall back to DDR then SDRAM if that fails.

Single- vs. Dual Channel
Very minor, but you should know the terms. Newer memory is "dual channel" memory, which means that information can flow two directions at once. Obviously, this is much faster than "single channel" memory. Both DDR and DDR2 are dual channel, while SDRAM is single channel.

The Front Side Bus
Remember that we talked about the front side bus in the processor section, and said that the speed of the FSB determines how fast the processor can pull information out of memory? Now that you know your FSB speed, you have to get the memory to match. Modern computers allow you to use memory up to the speed of the FSB, so make sure you have the fastest memory your system will support. The goal is to get a lot of memory at a reasonable speed for a reasonable price. And this is a balance, because just like processors and hard drives, the faster you get, the more you pay per MHz increase in speed. After about 1GHz, it becomes unreasonable (not to mention unnoticeable) for the average user.

Here's a chart that will help you pick the right memory for your FSB...

For a new PC, if your FSB supports it, I recommend at least DDR2 667 (PC2 5x00) RAM. More than that is hard to come by for an "average user" PC.

Buffering and Error Checking
There are a few remaining technical terms you should be aware of when purchasing RAM for your new computer. These don't really matter, from a performance perspective, but I don't want you to get lost in terminology limbo. Don't let dealers convince you that either buffering or error checking (also called parity, or ECC) is a selling point. It doesn't really matter. Just make sure that you get the right memory for what your PC supports, which is a topic on which you'd trust the dealer.

Brand
I'd love to tell you to get a certain brand, but you almost never get a choice. You'll get what they give you - whoever "they" is - unless you build it yourself, which is probably out of the question for average users. This plays into a general principle I share later in the article about picking a respectable manufacturer for the overall system because you know you'll get quality parts inside. A computer's like a car ... all this brand stuff matters.

That said, if you do have the choice, get Kingston ... which is an excellent brand, very affordable, and I've almost never had any problems with it.

Upgradeability
The only stuff that's easier to swap out / upgrade than your memory are your peripherals - printer, monitor, mouse, etc. Memory is by far the easiest thing that's inside the box to change out after your purchase. It also comes down in price the fastest. But be careful, make sure a computer geek picks out the right memory to go with your machine if you upgrade. Unlike hard drives, one size does NOT fit all.

Let's cut to the chase...
So, here's what I recommend... At least 1 GB of memory (2 GB is preferable) of DDR2 800 (PC2 6400) RAM, which will run on a box at a FSB speed of 800 MHz.

Introduction
Overview

The Parts of the Modern PC:
Processors | Hard Drives | Memory | Other Hardware | Software

Smart Buyers Will Also Consider:
Manufacturer (Where to Buy) | Service Plans and Warranties | Prices (What to Pay)

Conclusion:
The Final Word

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