ASCII is a 7-bit text encoding. ASCII stands for American Standard Code for Information Interchange.

To be valid ASCII, each character’s value must fall within the range of 0 to 127; this limit is imposed because only 7 bits are used to encode each character. One byte (8 bits) is used to store each character but only the 7 least significant bits may be used: any character with the 8th bit set is not valid ASCII.

Of the 128 possible characters, 95 are printable (that is, they are visible on the screen with the exception of the space character which appears as a blank space). The printable characters include all lower and uppercase letters of the Roman alphabet, the digits 0 through 9, and various punctuation marks such as !, ? and /.

The other 33 characters are non-printable control characters such as tab, backspace and delete.