What is a CPU (Central Processing Unit)?

The CPU is the heart of your computer. It contains the computing power that is essential for the tasks your PC has to handle on a daily basis.

The abbreviation CPU refers to the Central Processing Unit of your computer. It is often simply referred to as the processor. The processor is the central hardware component and the heart of your PC. Without it, a computer cannot function at all. This is mainly because the CPU is responsible for all calculations that are necessary for the PC’s operation.

To understand the importance of the CPU, it is necessary to understand the basic function of a computer. The computer’s calculations are performed by machine instructions, which you can think of as instructions to the processor. All machine instructions can be represented as sequences of ones and zeros, or binary code. This also happens in your computer because the CPU can only process binary instructions.

There is not one processor, but a whole range of different CPUs. These can be distinguished primarily by the number of processor cores. However, the field of application of CPUs also allows differentiation between different processor types. Of course, manufacturers vary, but the market is dominated by two companies in particular, Intel and AMD.

Single core CPUs only have a single processor core. This means that they can only process one task at a time. They are the oldest CPUs and are now only rarely used because parallelization plays a central role in many modern applications.

The counterpart to single-core processors are multi-core CPUs. They are characterized by the fact that they have several cores. They often have two or four processor cores (dual or quad core), but a larger number of cores is not uncommon. Processors with a very large number of cores are used especially when running servers. The advantage of multi-core processors is obvious: Due to the different, independent units, they can execute several tasks in parallel and enable smoother and faster work.

If you work with a conventional desktop PC, you are using a desktop CPU. These are the processors installed in PCs. Many modern desktop processors also include an integrated graphics card, which is sufficient for standard applications.

Basically, there are no major differences between desktop and mobile processors. In most cases, they mainly differ in power consumption. In general, desktop CPUs are considered more powerful than their counterparts installed in mobile devices like notebooks.

Processors used inside servers differ from CPUs in laptops and PCs. They have a much higher number of cores to efficiently execute many simultaneous operations. In addition, servers usually run around the clock, so the high load can be compensated with the number of cores.

The processor performs the essential tasks of your computer. They can generally be distinguished in the following three ways:

1. Processing instructions. The computing unit is responsible for processing the received instructions and returning corresponding results.
2. Communication with the input and output devices or peripherals. The control unit is responsible for this. It also takes care of the interaction of individual processor components with each other.
3. Data exchange. A conventional PC consists of many components, e.g. different types of memory or the graphics card. With its system bus, a processor ensures that data can be sent back and forth between the components.

In addition to these central components, CPUs can also contain other components that have become indispensable in modern processors:

• Memory Management Unit: The Memory Management Unit, or MMU for short, manages access to the computer’s main memory or RAM by translating virtual memory addresses into physical ones.
• Cache: The cache is often a multi-level, fast buffer memory.
• Floating point unit: The floating-point unit is a specialized computing unit responsible for handling decimal numbers.

The processing of individual instructions within the CPU happens incredibly fast. For example, when you press a key on your keyboard, you normally see the corresponding letter on your monitor without delay. Nevertheless, many steps are running in the background for the processing of instructions to run smoothly. The basic sequence of command processing can be divided into four essential phases:

1. Fetch: First, the address of the next machine instruction is read from your computer’s memory.
2. Decode: Then the instruction is decoded, and the corresponding circuits are loaded.
3. Fetch operands: Then all parameters required for the instruction are loaded into the registers. The values that are written into the registers can be found either in the main memory, in the working-memory or in cache.
4. Execute: Finally, the command is executed.

These four phases are repeated practically in a continuous loop: as soon as a command has been completed, the next command is selected and processed by the processor. The order in which the commands are executed depends on scheduling procedures. Through appropriate planning, they ensure that the system behaves in a balanced manner.

How powerful a processor is, depends on several factors. On the one hand, the word width is relevant. This specifies how long a machine word can be. For example, it determines how many bits can be read from the main memory at the same time or in which range integer or floating-point numbers can be processed. Most common computers have a word width of 32 or 64 bits.

The number of CPU cores also plays a decisive role when you want to assess the performance of a processor: The more cores a processor has, the more tasks can be processed in parallel. Load distribution within your system also works better with an increasing number of cores.

However, it is not only the number of cores that matters. At least as important for the performance of a CPU is the clock frequency with which the individual cores work. The clock frequency is specified in Hertz or Gigahertz. Basically, the higher the clock frequency, the more machine instructions can be processed by the CPU per second.

However, the mainboard’s base clock also plays a role for the clock frequency, which can be set manually in BIOS for some mainboards. Furthermore, the clock frequency can’t be increased arbitrarily, but is always limited by the CPU temperature. If this increases too much, the processor can be damaged under certain circumstances. Not least because of this, overclocking CPUs also requires some know-how.

What is more decisive for CPU performance: the number of cores or the clock frequency? Unfortunately, there is no clear answer to this question. It not only depends on the application, but also on the processor itself.

Modern processors are often more efficient in processing instructions and can therefore also provide the same performance with a lower clock frequency as older processors with a higher clock frequency. In addition, modern processors often offer the possibility for multithreading or hyperthreading, so that several threads can be executed in parallel on one core.

If you run applications on your computer that benefit from multiple cores and parallelization, then it is worthwhile to resort to a correspondingly high number of processor cores to distribute the CPU load in the best possible way. Such applications include the use of virtual machines or rendering. This is because the workload of such programs can be distributed very well.

If you mainly use your PC for applications that can’t distribute their workload that well, for example computer games, then the clock frequency becomes more decisive.

Modern processors often have an intelligent workload distribution across the CPU cores. If the current workload can be efficiently distributed across several cores, this is exactly what is done, and all available cores are used. The individual cores then run at a lower clock frequency. However, if the use of multiple cores is not sensible or necessary, then the clock frequency of the cores used is increased.