ASCII is the most common format for text files in computers and on the Internet.
In an ASCII file, each alphabetic, numeric, or special character is represented with a 7-bit binary number (a string of seven 0s or 1s). 128 possible characters are defined. UNIX and DOS-based operating systems (except for Windows NT) use ASCII for text files.
Newer versions of Windows use a newer code, Unicode. IBM’s System 390 servers use a proprietary 8-bit code called EBCDIC. Conversion programs allow different operating systems to change a file from one code to another.
ASCII was developed by the American National Standards Institute (ANSI). A chart of ASCII characters and their decimal or hexadecimal equivalent can be found at asciitable.com