Glossary:Central Processing Unit (CPU)

Introduction

The CPU (Central Processing Unit) is one of the primary devices that enables a computer to do work. It performs the instructions of a computer program. CPUs today are rated by the number of cores per die they feature, as well as the speed of each core. Today CPUs can contain anywhere from 1 to 8 cores on the die (or higher for server CPUs).

Technologies

Multi Core

CPUs featuring more than 1 core per die are said to be multi-core. Almost all CPU's that are made today are multi-core, meaning they feature 2 or more cores per CPU die. Many laptops today feature CPUs with 2 cores. Desktop computers can feature 4 or more cores. Common core configurations include single-core (1 core), dual-core (2 cores), quad-core (4 cores), 6 core and on very high end devices even 8 cores. AMD also sells processors with disabled, malfunctioning cores at a lower price. These include, but are not limited to, single-core and triple-core processors, which are respectively dual-core and quad-core processors with a disabled core. It may sometimes be possible to unlock a disabled core, but remember that these cores are disabled for a reason and like over-clocking, unlocking them will most likely void your warranty.

Single-core processors in desktops are mostly considered legacy devices nowadays, but more cores are not always better. Many games fail to use more than two threads (or two cores) and while a processor may be fast with all its cores enabled, a CPU with a lower number of cores but with higher performance per core will probably do better in most games. Like the clock speed of a CPU, the amount of cores should not be directly used as a guide to choosing the fastest one.

Speeds

CPU speeds can range anywhere from 1.0 GHz to over 3.4 GHz stock. Speeds for a CPU are measured in terms of MHz (megahertz) and GHz (gigahertz), and measure the speed of the clock signal going through the CPU. CPU clock speed should not be used to judge weather or not one CPU is faster, nor should core count.

Turbo

Turbo is the name for the technology used by Intel and AMD to run a CPU at a higher frequency when it is stressed. For example, an Intel Core i7 2600k runs at 3.4 GHz stock, but turbo increases it to 3.8 GHz. This is especially useful for gamers, as Turbo technologies often kick in when not all cores are used, as is often the case while gaming.

Over-clocking

Over-clocking is causing a CPU to run at speeds beyond what the manufacturer recommends. Over-clocking can damage the CPU if performed improperly. Often times, the stock cooler is inadequate for CPU over-clocking.

Please note that over-clocking will probably void your warranty and that it increases the chance of a CPU malfunctioning. Over-clocking is done at the risk of the user and is not recommended for novices.

Graphics

Some CPUs can feature combined graphics capabilities. These graphics capabilities may be adequate for web surfing, but are often not adequate for high end gaming. Intel's first CPU line that featured these capabilities was their Nehalem architecture. AMD also provides CPUs with on-board graphics under the Fusion name. AMD calls these chips APUs (accelerated processing unit) and they are much faster than their Intel counterparts at this time. While Fusion APUs will also not provide a great high end gaming experience, most games will run quite well on these chips, even though the graphical fidelity might need to be reduced to achieve reasonable frame rates.

Intel

Intel's initial offerings in the consumer GPU space were under the Intel Graphics Media Accelerator (GMA) brand, and served only to provide basic video functionality to PCs. Very near the end-of-life for the GMA brand, Intel's chipset integrated chips began to compete with older, very basic GPUs from Nvidia and AMD; they are able to play old games at reduced settings. Recently Intel began moving away from chipset integrated graphics, and with the Core i3/5/7 line of chips began offering GPUs combined with the CPU. The current best offering is their HD4000 graphics core, found in some Ivy Bridge chips; it is capable of competing with basic cards in the current generation.

AMD

AMD processors are often cheaper than their Intel counterparts, but recent Bulldozer CPUs have been less comparable in terms of their performance. These Fusion APUs are available for both embedded appliances as well as desktops, the latter using the Llano architecture, are mounted on socket FM1 and are sold as A4, A6, A8 (2, 3, 4 cores respectively) processors. There is currently also an E2 line-up available with 2 cores. The fastest GPU offered by the Fusion series is the HD 6550D, which trades blows with the NVIDIA GeForce GT 240 for gaming performance.

General Advice

Troubleshooting

When a CPU is malfunctioning, the problems can range from something as simple as higher temperatures to the inability to boot. The first step is to thoroughly test all other components to make sure that the CPU is the problem. If you are still certain, monitor the CPU temperatures with CoreTemp. If temperatures regularly go over 70 °C, then you may have a heat problem. Make sure that the heat-sink is fully fastened, and if it is, make sure that you applied a proper amount of thermal paste (Note: checking the thermal paste will require you to clean off and then reapply more thermal paste, so only check this as a last resort.)

Another problem that may arise with the CPU is improper seating. If you are experiencing random freezes and blue screens, you may have bent pins on the CPU. To check this, you must separate the CPU from the CPU socket (check your CPUs documentation on how to do this) and visually look for bent pins.

Choosing a CPU

Megahertz myth

A common misconception, especially to novice buyers, is that the higher the clock speed on a CPU is (the clock speed is easy to find and looks something like 2666 MHz or 3.2 GHz), the faster the CPU is going to be. This used to be the case many years ago and is still the case when comparing processors from the same architecture. For example, an Intel i3 2120 is clocked at 3.3 GHz and is faster than an Intel i3 2100 which is only clocked at 3.1 GHz, a 200 MHz decrease. This is valid because the clock speed is the only difference between these two processors. On the contrary, however, an Intel i3 2120 at 3.3 GHz will be vastly slower than an Intel i5 2400, which is actually clocked 200 MHz lower at 3.1 GHz, because of various other factors like the amount of cache memory on the chip, the amount of transistors, the number of cores and several other factors.

A good way of telling if a CPU is faster than another is to look at benchmarks. Benchmarks are tests where processors are put to work and are compared in their real world performance afterwards. A simple Google search can give plenty of results for almost any CPU. Remember to do your research before spending money on a processor.

External links

CPU article on Wikipedia