At the heart of the computer is the microprocessor.
This contains several REGISTERS to store data and an ARITHMETIC LOGIC UNIT (ALU) which manipulates data.
It acts as the central processing unit (CPU) of the computer, carrying out a sequence of instructions, called a program.

The program may be stored in memory, as software, or written into the memory from tape or disk.

There are two types of memory.
Read Only Memory (ROM) which stores software permanently. The software is not lost when the computer is switched off but the stored data cannot be changed.
Random Access Memory (RAM) which can be written to and read from.
The stored data is volatile.
It is lost when the computer is switched off.

The actual computer, its case and printed circuit boards etc are known as hardware.

The computer needs to communicate with the outside world.
It does this via interfaces which are usually a plug or socket of some type.

The computer is a digital device.
It may need to communicate with an analogue device such as a loudspeaker or variable speed control.
To do this it uses digital to analogue and analogue to digital converters.