Characters in computer systems are represented using ASCII codes, which assign a unique number to each character.

ASCII, or American Standard Code for Information Interchange, is a character encoding standard designed to represent text in computers and other devices that handle text. Each character is associated with a unique number ranging from $0$ to $127$, corresponding to a specific character. For instance, the ASCII code for the capital letter ‘A’ is $65$, while the code for the lowercase ‘a’ is $97$.

Originally developed from telegraphic codes, the ASCII standard was first published in $1963$ by the American National Standards Institute (ANSI) and has undergone several revisions since its inception. The standard defines a total of $128$ characters: $33$ of these are non-printing control characters (many of which are now obsolete) that influence text processing, while the remaining $95$ are printable characters.

ASCII codes facilitate the transmission of data between computers by representing all necessary punctuation and control characters (such as carriage return and line feed), alongside all letters and digits. This capability makes ASCII an invaluable tool in the realm of computing.

The ASCII system is primarily based on the English alphabet and encompasses all characters typically found on a standard keyboard. However, it does not support special characters from non-English languages. This limitation led to the creation of alternative character encoding schemes, such as Unicode, which can accommodate characters from a wide array of languages and scripts.

In a computer, ASCII codes are stored as binary numbers. For example, the ASCII code for ‘A’ (which is $65$) is stored as the $8$-bit binary number $01000001$. This binary representation is utilized in the underlying hardware of computer systems.

In summary, ASCII codes provide a standardized method for representing characters in computer systems, enabling the reliable and efficient storage and transmission of text data. Despite its limitations, ASCII continues to be widely used and serves as the foundation for more advanced character encoding schemes.