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  • What makes a computer fast?
    Comparing the speeds of computers is like comparing speed skaters. You may be able to see who wins a race, but you'd be hard-pressed to pick the exact attribute that made the winner faster. Was it the legs? The trim figure? The stamina?

    With computers, a lot of people point to the "CPU" as the one attribute that wins the race. While this isn't a ridiculous way to judge computers, it's also not the full story. This week's Tech Tip explores a few of the many elements that go into making a computer fast

    What's a CPU?
    CPU stands for Central Processing Unit, though it's just as often called a processor. Some people think of the processor as a kind of brain, because without it, your computer can't do the simplest calculations needed to operate. But another way to think about the processor is that it's just a simple (but very fast) calculator. It just follows instructions from the programs on your computer (including the operating system itself, like Windows XP, or Mac OS X).

    So, a program tells the processor to get certain numbers from the memory, do some arithmetic on them, then hand the results back. The program itself
    then takes the results and interprets them in a way that you understand (for example, a program interprets a bunch of mathematical results to show a picture of your uncle eating a hot dog).

    Without getting into the magic of how numbers can look like Uncle Rick, we can at least understand that the faster a processor can do calculations, the better your computer can show you pictures, open programs, and do all those other things you use your computer to do.

    So how fast can a processor calculate? The answer to that question takes us into the world of megahertz and gigahertz.

    Uh, Megahertz? Gigahertz?
    Simply speaking, a 1 megahertz (MHz) processor can execute about a million calculations per second. A gigahertz (GHz) is about a thousand times faster than a megahertz.

    Four or five years ago, it wasn't surprising to find processors running at 500 MHz, or 500 million calculations per second. Pretty fast. And today? If you're not performing 2 BILLION calculations per second (2 GHz), well, you're not really trying.

    To be sure, most of the things that people do on a computer, like emailing, surfing the Net, or chatting, don't need very fast processors. But the newer operating systems need faster processors to look and perform as well as they do. And if you like gaming or digital image processing, that speed can make a real difference.

    So is a computer with a 2 GHz processor really 4 times faster than one with a 500 MHz processor? Probably not.

    Processor Speed is Not the Whole Speed Story
    Imagine you're the world's fastest mathematician (if you ARE the world's fastest mathematician, this will be easy to do). You're in a race to be the first to write down, then turn in, the answer to the problem 2 + 2 = X. You're a shoe-in.

    But wait, what if you don't have a pen? Or the professor you're supposed to give the answer to has wandered off for an egg salad sandwich? You can calculate like a star, but if there's a bottleneck further down the line, you'll lose to the well-armed 3rd grader with an attentive teacher.

    The processor in your computer calculates really quickly. But even if you have the fastest calculator in the world, you first have to know what to calculate, then deliver the results and maybe write the results down. In other words, calculating is only some of the battle.

    The same kinds of bottlenecks (like writing and delivering data) plague computer manufacturers and users. The speed of any given computer depends on processor speed, but also on too many other variables to mention here. The biggies include amount of RAM, amount of Cache, BUS speed, and Hard Disk speed. Egg salad is way down the list.

    RAM stands for Random Access Memory, and is a big part of how quickly a program can perform tasks. We covered RAM in much more detail in the eLink #79 Tech Tip, RAM 101. For this topic, it's enough to say that the RAM temporarily "remembers" all the little details that a program needs to know. The more RAM you have (like 800MB rather than 500MB), the more your computer can remember at once, and the faster the programs can run.

    Usually pronounced like CASH, this kind of memory is super-fast and super-expensive. Regular old RAM is pretty fast, but can't really keep up with a processor doing billions of calculations a second. With plenty of speedy cache memory, that bottleneck is eased. But because of the price, most computers don't come with more than a megabyte or two of cache. (There are different kinds of cache, but we're just talking about the fast memory kind here.)

    The Bus
    A bus, in a computer or on a street, delivers something from one place to another. Think of a bus stop outside the stadium after a big game. People can run from the stadium door to the bus stop, but if the buses are slow, they have to wait right there. It's a bottleneck.

    The bus in a computer collects data from the processor and delivers it where it's supposed to go (the RAM, the display controller, and the hard disk, are a few examples), then gets instructions to bring back to the processor. (This isn't metaphorical. That data, even though it's in the form of electrical impulses, literally has to travel from one place inside the computer to another.)

    If the bus is slow, it doesn't matter how fast the processor is. Just like all those people waiting to go home outside the stadium (and it's starting to rain), the data just sits there waiting to be delivered to the programs that can use it. The computer just isn't as fast as the processor's speed suggests.

    There are two pieces to figuring how fast the bus can move data: width and speed.

    Bus Parts
    The width is pretty standard today. Most buses are 32 bits wide (a bit is the smallest piece of data that a computer can understand. Eight bits equals a byte, and about a thousand bytes is a kilobyte). This means that, rather than deliver one bit then go get another one, instead they can deliver 32 bits simultaneously.

    Bus speed can vary even in new computers, so it's something to watch out for. Rather than measuring calculations (as in processor speed), bus speed refers to how fast a bit of data can be delivered. These days, a 667 MHz bus isn't out of the ordinary, and they've got faster ones out there, too. If you can get faster, then you'll get a lot more out of your processor speed, and leave fewer bits waiting to be delivered.

    Hard Disk
    The hard disk is a storage bin for data your computer keeps awhile (or at least until you erase it). For example, when you save a file, your computer "writes" the file onto the hard disk. Later, when you want to use that file again, the computer has to "read" the hard disk. If this writing and reading is slow, your computer can feel sluggish.

    We won't go into how a hard disk works, but it's important to know that it literally spins around inside your computer, just like a record or CD. The faster it spins, to a degree, the faster your computer can read and write.

    Spin Speed
    This spin speed is measured in revolutions per minute, or rpm. Most computers today spin their hard disks at either 5400 rpm or 7200 rpm, though some are even faster. To put that in perspective, a 7200 rpm disk goes around 120 times per second!

    And the Rest...
    This tip is just a general introduction to the many pieces that go into making a computer fast. Each piece in the box is important in its own way, but the ones we mention above stand out as playing the biggest part.

    If reading all about speed has gotten you interested in what's under the hood of your own computer (and how to speed it up without spending the bucks):

    Check out your computer's goods:
    Windows users: Right-click My Computer and choose Properties. Mac users: Click the Apple menu, then choose About This Mac, then More Info.

    Speed up your own computer (without spending money):
    Visit the eLink #59 In Focus Speeding Up Your Computer.

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