What is the CPU?

The CPU (Central Processing Unit) is the heart of the computer. It executes the instructions of the programs and the operating system and It is made up of several billion transistors which process information in the form of bits (which have a value of 0 or 1).

Ryzen 5 3600 CPU

What are the main characteristics of a CPU?

  • The number of cores and threads: the higher the number of cores, the more tasks the CPU will be able to execute in parallel. This is a simple way to improve the performance of a computer because the core contains the transistors needed to execute the instructions of a program. In addition to multiple cores, some CPUs also have two threads per core, which allows them to execute certain instructions in parallel and  therefore increase the performance. In 2021, mainstream desktop CPUs have between 2 and 16 cores while the CPUs used in laptops have between 2 and 8 cores.
  • The frequency expressed in GHz: the higher the frequency, the faster the CPU will be. Nowadays the CPU frequency is usually not constant, modern CPUs can temporarily increase their frequency to perform heavy tasks or lower it to reduce power consumption and heat output. In 2021, the base frequency is generally between 2 and 4 GHz for the CPUs used in desktop computers and between 1 and 3 GHz for the ones used in laptops.
  • Lithography process size in nanometers (or nm): the thiner the process, the more transistors there can be on the same surface. It influences the production cost (the cost decreases if more CPUs can be manufactured from the same silicon wafer) and the complexity of the CPU (more transistors can be included in the same area). In 2021, the process size is between 7 and 14 nm for AMD and Intel CPUs.
  • The thermal design power (or TDP) in watts (or W): it corresponds to the energy that the CPU cooling system must be able to dissipate for the CPU to operate correctly. It is linked to the power consumed by the CPU but watch out as this one can be far greater as you can see in this page. In 2021 the TDP is between 5 and 55 W for the CPUs used in laptops and between 35 and 165 W for those used in desktop computers.
  • The CPU socket: it is specific to the CPU manufacturer. In 2021, Intel desktop CPUs use the FCLGA1700 (Alder Lake CPUs) or FCLGA1200 (Intel Rocket Lake and Comet Lake CPUs) sockets. Previous generations of Intel CPUs used the FCLGA1151 socket. On the other hand, AMD desktop CPUs use the AM4 socket.
  • L1, L2 and L3 caches: RAM memory is fast but microprocessors are even faster. CPUs therefore have different levels of small, ultra-fast memories called caches where program instructions and data are copied in order to improve their performance. Modern microprocessors generally have three levels of caches. The level 1 cache (L1) is very small (a few tens of kilobytes per core) but it is the fastest with speeds that can reach several terabytes per second. The level 2 (L2) cache is larger (a few hundred kilobytes per core) but a little slower, finally the level 3 (L3) cache can have several megabytes but is also the slowest (with a throughput of several hundreds of gigabytes per second). The level 1 and 2 caches are generally specific to each core while the level 3 cache is shared between the CPU cores. Usually, a larger amount of cache will improve the performance of the CPU.

Price and choice of CPU:

In 2021, the two main manufacturers (Intel and AMD) are offering many CPUs for different price ranges. Their prices vary from a few tens of euros or dollars for the low end to over a thousand euros or dollars for the high end CPU. Some manufacturers use other CPUs based on an ARM architecture for ChromeBook laptops or some Apple computers introduced in late 2020.

The choice of a CPU will depend on what the computer will be used for. For light usage (word processing, spreadsheet, internet browsing, social networks) low-end CPUs will be sufficient. For more intensive tasks (video games, video editing, scientific computing for example) you should choose a middle-range or high-end CPU.

Intel’s entry-level CPUs are the Celeron, Pentium and Core i3, the mid-range are the Core i5 and the high-end are the Core i7 and Core i9. On the AMD side, the entry-level consists of the Athlon and Ryzen 3 CPUs, the mid-range are the Ryzen 5 CPUs and the Ryzen 7 and Ryzen 9 are the high-end CPUs.

Both manufacturers offer a new generation of microprocessors almost every year in order to improve the performance and features. Intel introduced the 11th and 12th generations of Core CPUs called Rocket Lake and Alder Lake in 2021 while AMD introduced the Ryzen 5000 or Zen 3 series of CPUs in 2020.

Some CPUs have an integrated graphics solution for the 2D or 3D graphics and computer video. It is enough for a light usage or for simple or old video games and it reduces the cost of the computer. But it will nevertheless be necessary to add a dedicated graphics card to play modern video games in high resolution. You can consult the graphics cards page for more information.

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