1. RAM & ROM

RAM
i) It stands for random access memory.
ii) It is an optical disc, where data and information is stored permanently.
iii) RAM is the primary storage media.
iv) RAM is the primary storage device from which the system boots.
v) RAM is stored on RAM chip.
vi) The data or information stored on it can be written on or it can be erased.

ROM
i) It stands for read only memory.
ii) It is that part of CPU, where temporary information is stored.
iii) RIOM is the secondary storage media.
iv) System does not boot from ROM.
v) ROM is stored on a compact disc.
vi) The data or information stored on it neither be written on, nor it can be erased.

2. BIT & BYTE
A bit is defined as: a single basic unit of information, used in connection with computers and electronic communication. All modern computers store and use data in digital form. The smallest unit of storage and measurement is one binary digit, therefore its name.
A byte, pronounced ‘bite’, is the next size up basic unit of measurement for information storage, usually consisting of eight bits. These 8 bits are grouped together to form a byte that is, a total or 8 grouped bits representing one character of data.
Therefore, so far we have two basic units of measuring digital information storage that have different capacities, they are:
• 1 Bit
• 8 Bits equal 1 Byte

3. CU & ALU

CU
i) It stands for Control Unit.
ii) Control unit controls overall activates of computer.
iii) CU does not perform the functions of calculations.

ALU
i) It stands for arithmetic logic unit.
ii) It performs arithmetic and logical operations.
iii) ALU performs functions of addition, subtraction, multiplication and division.

4. Hardware & Software

Hardware:
i) All the physical components of computer which can be touched, measured have weight and occupy space are collectively called computer hardware etc.
ii) Examples of hardware are: keyboard, mouse, joy stick, scanner, printer, CPU etc.

Software:
i) Software can be defined as a set of instructions and codes written in a defined manner. In other words software are pre-written programs, which control the operation of computer.
ii) Examples of software are; DOS, windows, UNIX, XENIX, Linus, JAVA, Oracle, Antivirus etc.

5. PC/Minicomputers & Mainframe computers

PC:
i) It is a small computer based on microprocessor.
ii) One user can use it at a time.
iii) These are very low priced computers. An individual can afford it.
iv) User friendly software are used to operate this computer.
v) Minicomputers were launched in 1959 by Digital Equipment Corporation (DEC)
vi) Minicomputers are also made by Data General, Hewlett-Packard & IBM

Mainframe Computers:
i) The largest computers called mainframe computers are the oldest category of computer system.
ii) They are capable of great processing speed and data storage.
iii) These are always kept in air-cooled rooms.
iv) They are mainly used in banks, airlines and industrial companies.