Characters and strings of text:

Characters and strings of text:
A personal computer processes textual information. Individual key-strokes generate letters, numbers, or other symbols that are called characters. Groups of characters treated as units are called strings. Since characters and strings can’t be processed directly by machine that “understand” only binary numbers, they must be encoded in some kind of binary code. The computer uses coding system called ASCII (American Standard Code for Information Interchange). ASCII associates a unique 8-bits binary with each character symbol.
The standard ASCII uses 7 bits to encode a character. Thus, 27=128 different characters can be represented. This number is sufficiently large to represent uppercase and lowercase characters, digits, special characters such as !,ˆ, and control characters such as CR (carriage return), LF (line feed), and so on.
Since we store the bits in units of a power of 2, we end up storing 8 bits for each character, even though ASCII requires only 7 bits. The eighth bit is put to use for two purposes:
1. To Parity Encode for Error Detection: The eighth bit can be used to represent the parity bit. This bit is made 0 or 1 such that the total number of 1s in a byte is even (for even parity) or odd (for odd parity). This can be used to detect simple errors in data transmission.
2. To Represent an Additional 128 Characters: By using all 8 bits we can represent a total of 28=256 different characters. This is referred to as extended ASCII.