Encoding text: ASCII, ISCII and Unicode

A computer understands only binary (0s and 1s). So when you press a key, the computer maps it to a unique code number, which is then stored in binary. For example, the capital letter 'A' has the code 65, which in binary is 1000001.

Encoding is converting data into an equivalent form using a specific code. Standard encoding schemes make sure that each letter, number and symbol gets the same code on every keyboard and every computer, so that text typed on one machine reads correctly on another.

Three important schemes:

• ASCII (American Standard Code for Information Interchange), from the 1960s. It first used 7 bits, giving 2⁷ = 128 different codes: enough for the English letters (capital and small), digits and common symbols, but only English.
• ISCII (Indian Script Code for Information Interchange), from the mid-1980s, uses 8 bits, giving 256 codes. It keeps the 128 ASCII codes as they are, and uses the rest (160 to 255) for the aksharas of Indian scripts.
• Unicode gives a unique number to every character of every written language in the world, the same on any device, operating system or software. Its common encodings are UTF-8, UTF-16 and UTF-32. Unicode is a superset of ASCII: the ASCII characters keep their old codes. The Hindi letter 'अ', for example, is 0905 (in hexadecimal).

An example: encode the word BIG in ASCII. B = 66, I = 73, G = 71. In 7-bit binary: 1000010 1001001 1000111.