User:Kerrick Staley/Engl 314 Processors

Introduction
The processor is the single most important component of your computer—it's your computer's equivalent of a brain. The processor (or CPU: Central Processing Unit) takes input, processes it (i.e. analyzes it) according to a series of instructions (called a program), and produces useful, meaningful output. The input can come from you, through the keyboard or mouse, from files and documents on your hard disk, or from other people around the world (via the internet, accessed through your network card). The output can go to your display (through your video card) or back to your hard drive or the internet. Input and output are not limited to what's listed here—see if you can think of other ways your computer "talks" with the world.

Speed
Depending on how it is manufactured, a processor's speed (how quickly it carries out tasks) will vary widely. Processing speed is a function of a number of other factors (see "What doesn't make a good processor?").

Benchmarks are the most useful tool (outside of buy-it-and-try-it) for evaluating a processor's speed. A benchmark is a program that does a large number of repetitive tasks, so that the time it takes to do all the tasks can be measured. How quickly or slowly a certain CPU executes a benchmark gives an estimate of its performance. There are several reputable websites (such as Tom's hardware) that run scores of benchmarks on a plethora of modern CPUs, to help guide you in your purchase.

Different benchmarks target different audiences: scientists may be interested in how many numerical calculations a CPU can perform in a second, so they'll be interested in benchmarks which do heavy number crunching. A CPU that's quick with numbers isn't necessarily as fast with other tasks, so you'll need to see if a benchmark is designed to match what you want to do with the computer. You'll probably end up doing a mix of different things on your new computer, so you should pick several benchmarks that related to something you'd do with your new computer, and use them when making comparisons.

Cache size
The cache (pronounced "cash") is a small amount of very fast memory that is built into the CPU. As a program executes, the processor will figure out which information in the main memory is most important to the program and save that information in the cache. Since the cache is a lot faster than the main memory, having a bigger cache means that your computer can process more information more quickly. Exactly how much extra performance you will get out of a bigger cache is hard to say; depending on which particular program you're using and which particular task the program is performing, a bigger cache could either make no difference whatsoever or cause an improvement of several hundred percent. The key point is that while all the other aspects of your new processor affect, more or less, the same thing (the speed), cache size is a distinct characteristic, and while processors with small caches are often significantly cheaper than processors with large caches (even if everything else is equal), the price drop can mean a big performance hit, or it can mean big savings without any difference to you. For your first build, you probably shouldnt't buy a processor that has an unusually small or unusually large cache compared to other processors in the same category.

Power consumption
The total amount of power your processor consumes may or may not matter to you. At the time of writing, the median Newegg processor (they currently carry exactly 100 models) has an 80 watt maximum power dissipation, and the median power supply (of 482 offerings) is rated for up to 600 watts, so a very rough estimate is that your processor will use 13% of your computer's power. Hence, if you're environmentally conscious, you'll only benefit from an energy-efficient CPU if you are also diligent with the rest of the system.

Compatibility
Your processor has to be compatible with your motherboard, but usually there are a wide variety of motherboards supporting a given processor. This just means that you should pick your processor before choosing a motherboard.

Brand name
The two most popular processor brands are AMD and Intel. While expert computer builders can be very opinionated and will sometimes insist upon one company or the other, in reality the brand makes very little difference. The processor market is fiercely competitive, and neither brand will typically be more or less powerful or expensive than the other, even though occasional technology breakthroughs allow one company or the other to gain a temporary lead.

Price
Usually, processor pricing is monotonic, more or less: a more expensive processor will generally be faster than a less expensive one. However, more expensive processors tend to have less bang-per-buck; tripling the price may only give you one-and-a-half times the speed. Furthermore, the value (total speed per dollar) of an average processor has historically followed a very consistent trend of doubling every 18 months (and there's no reason to think it won't continue), so the extra $100 you want to spend now might be better spent on another computer 3 or so years down the line. The key point is that even an entry-level processor will get you through many daily tasks like email and web browsing, and you only need to consider more expensive options if you have specific needs (like gaming).

Clock speed
The clock speed, which is usually expressed in gigahertz (GHz), indicates how many operations a computer performs in a second. It used to be a very important measure of how fast a processor is, but nowadays, multi-core processors and other advances have diluted the effect that the clock speed has on the overall performance, to the point that clock speed really doesn't mean anything. Still, two CPUs of the same model (a CPU's model identifies all its characteristics except for clock speed) can be directly compared on the basis of clock speed: a 3.0 GHz CPU will be exactly 50% faster than a 2.0 GHz CPU of the same model.

Number of cores
Modern processors contain multiple cores. A core is basically its own processor: each core of a multi-core processor has everything in it that an ordinary (single-core) processor does, so a multi-core processor effectively puts several processors into the same computer, working in tandem. Like clock speed, the number of cores really just affects the processor's overall speed, and it means very little on its own. Low-end processors are nearly always single or dual-core, since it is cheaper to focus on improving the cores themselves rather than adding more, so processors with 3 or more cores are typically more powerful, but again this can vary.

32 or 64 bit
"32 bit" and "64 bit" describe the word size of a processor. Processors with a 32-bit word size cannot efficiently use more than 4 GB of memory, whereas 64-bit processors can. When 64-bit processors were first introduced, there was a lot of speculation from consumers about whether or not they were really necessary, since most computers had significantly less than 4 GB of memory at that time. However, since then, memory sizes have increased, and it is almost impossible to come across a 32-bit processor any more.

Feature size
Another specification of a CPU that you will occasionally notice is the feature size, which is usually measured in nanometers (nm). The feature size of a processor is an indication of how small the components on the processor are, but it has no direct effect on the processor's performance: it just allows processor manufacturers to fit more complex and more powerful designs into the same space.