BLOCK DIAGRAM OF COMPUTER

Functional units of PC: 

-Control unit                         -  Arithmetic & logic unit(ALU)

- Main Memory unit             - Input unit

-output unit                           - Secondary storage.

1. Control Unit: This is the one of the central part of personal computer, which mainly control the operation. Its purpose to handle the processor control signal. It control the all the input and output flow in the computer system. basically it provide the communication between the input and output devices in computer system. It interpret the data or the information and send them for the further processing. It guide the computer flow between different media in system.

2. Arithmetic & Logic unit (ALU): It perform the arithmetical and logical operation and send them for the further processing It is the one of the main part of the central processing unit.  ALU has direct access to the processor for input and output . In some cases ALU divided into two part, first one the arithmetic unit (AU) and another one is logical unit (LU). AU perform arithmetic operation and LU perform the logical operation.

3. Main memory unit: This is a temporary memory. Where the data can be accessed randomly at any time. It is a volatile memory i.e its contents are lost when computer system is powered off. RAM is a volatile memory or temporary memory. It is normally of two type one is static RAM and another is dynamic RAM.

For more info click on Computer Memory:

4. Input unit: Computer is a device that take the input and give the output. So input unit basically include that input devices which is used to give the input to the computer system. This mean main purpose is to put the information in system by these devices. Input devices are like keyboard, mouse , scanner etc. There are various input devices that are discuss in the following links.

For more info click on the Input devices

5. Output unit: When any of the data or information sent by the system to any of the internal and external devices is a output. It include the devices like printer, speaker, desktop etc. for more discussion go and check the following link.
For more info click on Output devices

6. Secondary storage : Secondary storage mean permanent. Where we can permanent sore the data. It is non volatile memory. That mean contents are not erased or lost even your computer system is powered off.  There are another permanent storage like pen derive, CD, DVD etc are the some of the storage media where we can store the data for future use.

For more info click on Computer memory