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ASCII is the American Standard Code for Information Interchange.

ASCII codes are the 8 bit patterns of 1's and 0's (binary numbers) that represent text in computers and other devices that use text.

For instance the letters 'A' and 'a' is represented by:-

A = Decimal 65, hex:0101, Octal 0x41

a = Decimal 97, hex:0140, Octal 0x61

With numbers :-

0 = Decimal 48, hex:0060, Octal 0x30

9 = Decimal 57, hex:0071, Octal 0x39

And this means that if you subtract the ASCII character 0 (decimal 48) from the ASCII character 9 (decimal 57) you get the number 9. This is how keyboard keystrokes which are captured as text (ASCII) are converted into numbers in the computer when you need to do sums (e.g. in a spreadsheet).

There are other encodings that may also be used such as Extended Binary Coded Decimal Interchange Code (EBCDIC), but ASCII is the most common.

As a point of interest, with Roman character sets (which have about 127 characters) it is possible to encode most of the characters needed using just 8 bits (there is therefore room for 255 characters). However as use of computers spread and it became necessary to provide for different scripts such as kanji, which have many more characters to encode (the Yiti Zidian dictionary published in 2004 contains 100,000 or more individual characters) the character set used in computers and by programming languages had to be extended (by grouping bit patterns) to cope. The result is that you can type using kanji utilising a computer with a Chinese/Japanese keyboard. (Although how anyone can learn/remember 100,000 different characters is beyond my comprehension!).

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14y ago

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