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The CPU

The CPU is the "brain" of the computer. It's where most of the calculating is done. A computer's speed can be changed perhaps most by the choice of CPU.

Two main companies make CPUs: Intel and AMD. Intel is the No. 1 chipmaker with more than 90% of the market; AMD makes lower-cost CPUs for people on a budget. In this section, we will focus mostly on Intel, in part because they are the dominant CPU maker, and partly in order to keep things simpler.

When you buy a CPU, it comes as a single piece. It is usually flat, with hundreds of small metal pins or contacts on the bottom, and a chip casing on top. You never open or change the CPU physically. While you can replace a CPU with a different one, you cannot change an existing CPU.

The Need for Speed

CPUs have certain design points which can affect the speed. The main points are:

  • Model: This is the general name of the CPU, e.g. Pentium 4, Core 2 Duo, or Core i5. The model is usually (but not always) the most important indicator of speed.
  • Cores: A "Core" is the main area where calculations are made; recently, CPUs include 2, 4, 6, or more cores.
  • Clock Speed: This is a frequency, measure in GHzGigahertz; a "hertz" is one cycle per second, so a GHz is 1,000,000,000 cycles per second. The computer's calculations move forward one step for each cycle. Clock speed is mostly useful comparing different versions of the same model; when comparing different models, clock speed is meaningless.
  • Cache: Cache is memory located on the CPU, usually called L2 or L3 cache. 2-3 MB per core is considered fair.
  • Multi-threading: This is a feature where one CPU core can handle more than on calculation at the same time.

NOTE: The model of the processor (Core 2 Duo, i5, Xeon, etc.) is usually more important than the clock speed. Most people focus on the clock speed, thinking that a 3.0 GHz CPU will always be faster than a 2.6 GHz CPU. However, that is not true. For example, take this comparison between a Core 2 Duo at 3 GHz and a Core i5 at 2.66 GHz. You will notice that despite a lower clock speed, the Core i5 is a faster CPU:

Models, Versions, Types

Model lines are decided by the company that makes them. CPU models usually come in "generations," and there are often up to a half-dozen basic model types. For example, the Intel generation ending about right now (2010) included the Core Solo, Core Duo, Core 2 Duo, Core 2 Extreme, and Core 2 Quad. The new generation includes the Core i3, Core i5, Core i7, and Core i7 Extreme. A model line called "Xeon" are for powerful, workstationYou remember what a "workstation" computer is, don't you? No? Uh-oh... computers.

In any one generation, there are CPUs that are made for mobile computers and for desktops; there are slow, medium, and fast CPUs. Each model will have several (from 2-3 to dozens) of specific versions. For example, the Core i5 CPU by Intel has these basic versions:

  • 7xx: 4-core, 8MB L3 cache, no multi-threading (all current i5s have no multithreading)
  • 7xxS: 4-core, 8MB L3 cache, Medium-high-power usage
  • 6xx: 2-core, 4MB L3 cache, Medium-high-power usage
  • 4xx, 5xxM, 5xxUM: 3MB L3 cache, Low-power usage

Each version can have several types. Additionally, new versions and types come out every year or so while a generation continues. By the end of a generation, there is a long list of different CPUs. The Core 2 Duo, for example, had over 100 different versions before its generation ended!

So, Which CPUs Are Better?

To give you an idea of which Intel CPUs are faster than which other CPUs, here is a list of ones you can still get today in general order of power--weakest CPUs at the top, and strongest CPUs at the bottom:

Chip Use Notes
Atom mobile devices, netbooks The Atom is a very low-powered CPU made for very small computers which cannot cool themselves well
Celeron mobile devices, cheap desktops Celeron is the classic "cheap chip," with low price and low performance
Pentium 4 laptops & desktops Before the Core 2 Line came out, the Pentium 4 was the main CPU for Intel
Pentium Dual Core laptops & desktops Far better than the outdated Pentium 4, the strongest Pentium can beat the weakest Core 2 Duo--but the Core 2s are generally better
Core 2 Duo laptops & desktops The Core 2 series has been a strong challenger, but is beginning to show its age
Core 2 Quad laptops & desktops While the strongest Core 2 Duo can beat the weakest Core 2 Quad, the Core 2 Quads are generally better; the quads are not as common, though
Core i3 laptops & desktops The weakest Core i3 is about as powerful as the strongest Core 2 Duo. Still, the i3 is intended as the low-priced, low-power CPU of Intel's new line
Core 2 Extreme laptops & desktops A special chip, powerful but not used very often
Core i5 laptops & desktops Intel's new mid-range CPU
Core i7 some laptops, but mostly desktops Intel's new consumer-range power CPU
Xeon workstations The Xeon has always been a top-level power CPU for high-end workstations, but the name "Xeon" has been used for so long, that older Xeons are actually about as powerful as Core 2 Duos. However, new Xeons are in the same range as the most powerful i7 CPUs.

As you can see, the CPU models have some overlap, but it is generally possible to figure the ranking of a CPU by its name. With AMD CPUs, things are a little less clear, but generally AMD CPUs rank, from weakest to strongest, Athlon 64, Sempron, Turion, Athlon II, Phenom, Opteron--with the Opteron being the rough equivalent of Intel's Xeon. For test purposes, don't bother to remember the AMD names, but you should try to remember the Intel model names.

Sockets

The "socket" for a CPU means what design fits into a motherboard. For Intel, the main socket types today are:
  • LGA 775 (Core 2 Duo, Core 2 Quad, older Xeons)
  • LGA 1156 (Core i3, Core i5, some Core i7s)
  • LGA 1366 (Core i7, Core i7 Extreme, newer Xeons)

When you buy a motherboard, you must choose a CPU socket type; so you must know which CPU you will get. If the socket type is the same, then usually (but not always) you can change to another CPU. Many power users do this: they will buy a computer with a certain CPU, but later will upgrade to a more powerful CPU with the same socket type.