Basic Computer

Light Pen : A light pen is a light-sensitive computer input device, basically a stylus, that is used to select text, draw pictures and interact with user interface elements on a computer screen or monitor. The light pen works well with CRT monitors because of the way such monitors scan the screen, which is one pixel at a time, giving the computer a way to keep track of the expected scanning time by the electron beam and infer the pen’s position based on the latest timestamp of the scanning.

ASCII to Extended ASCII characters (8-bit system) and ANSI Code: In the 1960s, a need for standardization led to ASCII, which is a 7-bit system. But later almost everything was done in an 8-bit system. With 7 bits, 128 numbers (0-127 in decimal notation) are available to code characters. A bit is a binary digit which can have either two values, on or off. Seven bits can have 2^7 or 128 possible unique values. ASCII was soon expanded to an 8-bit system that has 256 code points, 0-255 (8-bit corresponds to 2 ^ 8 ie. 256 possibilities). There are many variants of Extended ASCII characters (8-bit system) to cover regional characters and symbols. One example is the extended ASCII characters which includes various letters needed for writing languages of Western Europe and certain special characters.
Source : wikipedia.org

The Enhanced Graphics Adapter is an IBM PC computer display standard from 1984 that superseded and exceeded the capabilities of the CGA standard introduced with the original IBM PC, and was itself superseded by the VGA standard in 1987.