Data Representation

The storage and processing of data are explained in terms of characters in the computer. The characters are represented electronically with a two-state binary system of numbers. A binary means two. The binary system is a fundamental principle of digital computers. Everything that goes into a computer is converted into binary digits, 0 and 1

Bit

A bit stands for BInary digT, and is a single digit in a binary number (1 or 0). That is each 0 or 1 in the binary system is bit. Physically, a bit is a cell in memory, a magnetic spot on disk or tape, and a pulse of high or low voltage through a circuit in the computer.

Bytes

A storage unit in the computer is groups of bits called characters, bytes, or words. The most common storage unit is the byte, which is made up of eight bits and typically represents a single alphanumeric character - number, letter, and special character.

Binary Code

What are the methods to code characters with 0s and 1s in the computer? There are many coding schemes. Among them, ASCII and EBCDIC are two of the most popular binary coding schemes. Both use eight bits to form each byte.

• ASCII: ASCII, pronounced "as-key, " stands for American Standard Code for Information Interchange. This is the most widely used binary code for data communications and microcomputers. ASCII is a 7-bit code, giving 128 possible character combinations. An extra bit is used to hold a parity bit.
• EBCDIC: EBCDIC, pronounced "eb-see- dick, " stands for Extended Binary Coded Decimal Interchange Code. EBCDIC is a binary code set for representing data and an 8-bit code that allows 256 possible characters combination. It was developed by IBM and is used on all IBM computers. EBCDIC is also almost an industry standard for minicomputers and mainframe computers.

Units of Capacity

The capacity of memory (primary storage) and a storage device is expressed in numbers of bytes, which start with 1 and double: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, etc. For example, when a microcomputer system is listed with an "8 MB main memory," the computer has primary storage capacity of around 8 million bytes. The capacity of disk, tape and memory is measured in bytes, whereas that of the CPU and memory chips is measured in bits.

• Kilobyte (KB): About 1000 bytes (precisely, 1024 bytes). A kilobyte is abbreviated KB or K-byte.
• Megabyte (MB): About 1 million bytes. A megabyte is abbreviated MB or M-byte.
• Gigabyte (GB): About 1 billion bytes. A gigabyte is abbreviated GB or G-byte. Today's high capacity microcomputer has around 1 GB hard disk space.
• Terabyte (TB): About 1 trillion bytes. A terabyte is abbreviated TB or T-byte. This is a measure used with mainframe computers and supercomputers.

Parity Bit

A parity bit is an extra bit added to a byte for error detection purposes in data transmission. Parity checking is accomplished by using a parity bit that is an extra bit automatically added to a byte for purposes of testing accuracy.
There are even-parity systems and odd- parity systems. In an even-parity system, the parity bit is set to either 0 or 1 to ensure that the number of 1s is even. Odd-parity systems perform the opposite.

Units of Space/Time

Space

Kilo (KB)	Thousand	1000
Mega (MB)	Million	1,000,000
GIga (GB)	Billion	1,000,000,000
Tera (TB)	Trillion	1,000,000,000,000

Time

Milliscond (ms)	Thousandth	1/1,000
Microscond (µs)	Millionth	1/1,000,000
Nanoscond (ns)	Billionth	1/1,000,000,000
Picoseond (ps)	Trillionth	1/1,000,000,000,000
Femtoscond (fs)	Quadrillionth	1/1,000,000,000,000,000