ASCII is an acronym for American Standard Code for Information Interchange. ASCII is a 7-bit character code where each separate bit represents a unique character. Computers can only understand digits, so this is where the ASCII character table comes in. It contains the numerical representations of a character like ‘b’ or ‘$’. ASCII was designed many years ago and now the non-printable characters are seldom used for what was intended. The ASCII character table was created to be used with teletypes and therefore the descriptions are hardly used anymore. If you need to create a text file in ASCII format, all that needs to be done is to create a ‘plain’ text file with no formatting like font color, bold or underscoring. This is a basic format that any software can operate with. On Microsoft Windows, Notepad creates ASCII text, or in MS Word has the option to save a file as ‘text only’.
Because the ASCII character table extensions have so many versions, there has to be a way to identify which set corresponds to every separate text so it could be understood properly. On the other hand, because the popular characters are included in all sets — including the most proprietary ones — unsuccessful identification of a character set usually doesn’t bear any consequences if the user is typing in English. Further, because many Internet standards use ISO 8859-1, and because Microsoft Windows (using the code page 1252 superset of ISO 8859-1) is the dominant operating system for personal computers today, unannounced use of ISO 8859-1 is quite commonplace, and may generally be assumed without evidence to the contrary.
Extended ASCII is a character table of codes that adds to the original ASCII set. The basic ASCII table uses 7 bits for each character, which makes a total of 128 separate symbols. The extended ASCII character table uses 8 bits, which gives it an additional 128 characters. The extra ones accommodate characters from non-English languages and special characters for creating drawings. The combined number of symbols which constitute human languages, mathematics, most programming languages and software applications far exceeds the 96 (128-32) printable ASCII codes, many extensions to it have been used. Because the ASCII character table is in 7-bit code and all modern PC’s operate with data in 8-bit bytes, many extensions use the additional 128 codes available by using all eight bits of each byte. Extended ASCII helps include many languages otherwise not easily expressed in ASCII, but is still not enough to cover all languages of countries in which computers are sold, so even these eight-bit extensions had to have local variants.