1) Software                2) Hardware                   3)    Data                4) User

Software: 

Software – also called programs – consists of organized
sets of instructions for controlling the computer.
Some programs exist for the computer’s use, to help it
manage its own tasks and devices.
Other programs exist for the user, and enable the
computer to perform tasks for you, such as creating
documents. 

Hardware:

A computer’s hardware consists of
electronic devices; the parts you
can see and touch.
The term “device” refers to any
piece of hardware used by the
computer,such as a keyboard,
monitor, modem, mouse, etc. 
 

Data:

Data consists of raw facts, which the computer can
manipulate and process into information that is useful
to people.
Computerized data is digital, meaning that it has been
reduced to digits, or numbers. The computer stores
and reads all data as numbers.
Although computers use data in digital form, they
convert data into forms that people can understand,
such as text, numerals, sounds, and images. 

User:

People are the
computer’s operators, or users.

Some types of computers can operate without much intervention from people, but

personal computers are designed specifically for use by people.