Explain the function of the central processing unit?

Answer 1

The purpose of the central processing unit is to do all necessary processing of data. It spends most of its time doing arithmetic but can manipulate data in other ways to depending on its instruction set. The instruction set is the set of things programs can ask the CPU to do. When it is done it sends the information back to the program that requested it so the program can finish its tasks.

Answer

The central processing unit (CPU) does all the general day-to-day processing within the computer. That is; it executes the machine instructions given to it by the operating system (which is just another program just like any other).

The instructions it executes are extremely simple and minute in the grand scheme of things, but the most of the work is achieved via logic circuits. These are finite-state machines, simple devices that accept one or two bits (binary digits) and output a bit, depending on the state of the input(s). When used together and in combination they can perform more complex tasks such as arithmetic and complex comparisons.

A simple task such as scrolling a list of values can easily generate thousands of individual instructions, each of which does a very minute fraction of the overall work. But they are executed with such speed that you'd be forgiven for thinking the CPU wasn't working at all. After all, when you look at your CPU activity monitor, 95% of the time it seems to be idle. But it's simply waiting for you to do something more useful than watching it idling. Give it a large file to copy and watch that idle figure tumble.

Bear in mind that the operating system may be running dozens of programs at the same time, some in the background, some in the foreground. It must give the CPU a little bit of time to each application, including itself, to give the appearance that each is running independently of the other. In truth, they are not; they are simply switching so fast you barely notice the pauses, although you will encounter them from time to time when an errant process fails to yield control to the operating system or the CPU is tied up with a hardware request. If you have multiple cores or processors, then simultaneous execution is indeed possible, but only one program has any one processor's brief but undivided attention at any one time.

The central processing unit isn't the only processor in your system, but it co-ordinates all the other processors, including the graphics processor, the audio processor and the maths processor. These other processors are "specialists". By delegating the work appropriately, the CPU can get on with its more generalised processing duties more efficiently.

The CPU is attached to the motherboard from where it has access to the system's main memory and all the peripheral devices attached to the motherboard, including internal and external hard-drives, and all input and output devices. Basically nothing happens without the CPU knowing about it.