CPS100 • Introduction to Computers

Lakeland College • Japan Campus

The CPU (Central Processing Unit)

Various parts of the computer process data by performing calculations. However, the part that does most of the work, and the most important work, is the CPU.

What Makes a CPU Fast?

As explained in the previous chapter, the CPU has cores and cache.

a map of a cpu die

The core is where the important work is done. Instructions from programs are processed here. Recently, most CPUs have multiple cores (called "multicore"). This allows the CPU to work faster. Generally speaking, the more cores, the faster the CPU will operate. It is similar to having more people do the same job; if one person can finish a job in 4 hours, then four people can finish the work in perhaps one hour. Cores do not work in exactly this way, but the idea is similar.

One program may access multiple cores for greater speed, or each program can use a single core so several programs can run quickly at the same time. Otherwise, it is like living in a house with four people but only one bathroom; at busy times, everyone must wait their turn.

CPUs today usually have at least two cores; four cores is becoming more common. Some mainstream CPUs have 6 cores, and some workstation CPUs have 12 cores.

The cache is the memory kept on the CPU. This is much faster than using memory from RAM. However, the CPU is small and "real estate" is valuable, so only a little memory—usually only a few megabytes per core—can be used in cache.

There are several levels of cache, called L1 cache, L2 cache, and L3 cache. Lower numbers are smaller and faster, but all types help with the CPU's speed. Generally speaking, more cache is better.

A liquid CPU cooling system
A liquid cooling system

It is commonly believed that clock speed is a good indicator of a CPU's speed. The clock speed is like a metronome for the CPU; it sets the pace at which operations take place, and how data moves in the pathways of the CPU.

If CPUs were 100% efficient, then clock speed would be an excellent indicator. However, some CPUs work much better than others. Lower-performance CPUs may make more errors and have to perform more corrections. Some CPUs may not be able to receive data quickly enough, and will have no data to process sometimes. Additionally, certain CPU designs and features can allow two CPUs with the same clock speed to process data at much different speeds. Multiple cores are an excellent example of this. Think about one person doing a job at a set speed. If another person joins them and helps, they can finish the job in half the time, even though they work at the same speed. It is similar with CPU cores.

More and more, because CPUs are run faster and faster, they become extremely hot. Most CPUs require cooling fans in order to keep them from overheating. These fans are what cause most noise coming from computers.

A CPU going into its socket
A CPU going into its socket

You can also increase the clock speed for a CPU you already have; if you do this, the CPU will run faster. This is called overclocking. It is only possible with CPUs that allow it. However, the CPU becomes far too hot. A special, powerful cooling fan is needed to allow the overclock. Sometimes, an extreme cooling system, sometimes using liquid cooling, is required. Some DIY computer cases allow for liquid cooling.

CPUs can often be removed and replaced. However, you can only put in a CPU that uses the same socket (a foundation, like a plug socket, which accepts a specific type of chip). This usually does not allow you to put in a much faster CPU; therefore, upgrading the CPU is not very useful, and can be very expensive.

Which CPU Do I Need?

This is an excellent question. If (1) you will use a computer for very limited purposes, like MS Word and the Internet, and (2) you will rarely or never upgrade your software, then probably any CPU will work fine for you for many, many years.

However, most people upgrade your software. Upgrades and other new software usually need greater speed; these will sometimes make your computer seem to "slow down." In fact, your computer is running at the same speed—it is just being asked to do more work! Eventually, your computer will seem to go so slowly that you may give up and buy a new computer.

Future-proofing is a technique where you buy faster and more powerful equipment so it will last a longer time. When you shop for a computer, you may only think about how fast the computer is for software you use today. If you future-proof, you must think about how fast your computer will be in 2 or 3 years, or more. You will get a faster CPU than you need today, and you will add more RAM than you currently need.

How Do I Know Which CPU Is Fastest?

CPU names are extremely confusing. With Intel computers, there are "families" (Pentium 4, Core Duo, Core i), "generations" (Sandy Bridge, Ivy Bridge, Haswell), "lines" (i3, i5, i7, Xeon), and "models" (E3500, 2500K, 4440S). Understanding them and keeping track is extremely difficult.

Fortunately, there is a way to get around that: benchmarks are the results of performance tests on a CPU which rate its speed. They are usually the best way to see which CPUs are faster than other CPUs. It is not a perfect system; a "faster" CPU may do very poorly at a specific task, like playing video files, or doing 3-D rendering, despite being extremely fast at most tasks.

An excellent benchmark site is Passmark, where you can see various lists but also can see a list of a few thousand CPUs going back several years. Anandtech has a fair list as well.

Terms to Know

CPUthe "brain" of the computer, where most processing is done.
corewhere the main processing happens in the CPU; program instructions are carried out in the core.
cachea temporary data holding area on the CPU; it is only a few megabytes in size, but helps increase the speed of the computer.
socketa special receptor in which a CPU sits. It has hundreds of small pins which connect to the bottom side of the CPU case.
clock speedthe rate (speed) at which a CPU works, measured in Hertz (cycles per second). The more Hertz, the faster the CPU. Most CPUs today work in gigahertz (GHz).
overclockto run a CPU at a speed faster than intended.
cooling fanrequired to cool the CPU.
future-proofingpurchasing a computer which is faster and more equipped than is necessary for the present, so it will work better and longer in the future.
benchmarkthe results of performance tests on a CPU which rate its speed.
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