Functional units of computer: 

A computer is not a single unit but it consists of many functional units(intended to perform jobs) such as Input unit, Central Processing Unit(ALU and Control Unit), Storage (Memory) Unit and Output Unit. 

1. Input Unit: 

Its aim is to supply data (Alphanumeric, image , audio, video, etc.) to the computer for processing. The Input devices are keyboard, mouse, scanner, mic, camera, etc 

2. Central Processing Unit (CPU): 

It is the brain of the computer and consists of three components 

• Arithmetic Logic Unit(ALU): As the name implies it performs all calculations and comparison operations. 
• Control Unit(CU): It controls overall functions of a computer 
• Registers: It stores the intermediate results temporarily.

3. Storage Unit(Memory Unit): 

A computer has huge storage capacity. It is used to store data and instructions before starts the processing. Secondly it stores the intermediate results and thirdly it stores information(processed data), that is the final results before send to the output unit(Visual Display Unit, Printer, etc)

Two Types of storage unit 

(a) Primary Storage alias Main Memory: 

It is further be classified into Two- Random Access Memory(RAM) and Read Only Memory(ROM). The one and only memory that the CPU can directly access is the main memory at a very high speed. 

It is expensive hence storage capacity is less. RAM is volatile (when the power is switched off the content will be erased) in nature but ROM is non volatile(lt is permanent)

(b) Secondary Storage alias Auxiliary Memory:

Because of limited storage capacity of primary memory its need arises. When a user saves a file, it will be stored in this memory hence it is permanent in nature and its capacity is huge. 

eg: Hard Disc Drive(HDD), Compact Disc(CD), DVD, Pen Drive, Blu Ray Disc etc. 

4. Output Unit: 

After processing the data we will get information as result, that will be given to the end user through the output unit in a human readable form. Normally monitor and printer are used.