ASCII and ANSI

ASCII (American Standard Code for /nformation interchange—pronounced "AS-key") is the most popular encoding system for PCs and data communication. In ASCII, alphanumeric characters are encoded into a bit configuration on input so that the computer can interpret them. This coding equates a unique series of on-bits and off-bits with a specific character. Just as the words mother and father are arbitrary English-language character strings that refer to our parents, 1000010 is an arbitrary ASCII code that refers to the letter B. When you tap the letter B on a PC keyboard, the B is transmitted to the processor as a coded string of binary digits (for example, 1000010 in ASCII), as shown in Figure 2-3. The characters are decoded on output so we can interpret them. The combination of bits used to represent a character is called a byte (pronounced "bite"). The 7-bit ASCII code can represent up to 128 characters (27). Although the English language has considerably fewer than 128 printable characters, the extra bit configurations are needed to represent additional common and not-so-common special characters (such as - [hyphen]; @ [at]; I [a broken vertical bar]; and [tilde]) and to signal a variety of activities to the computer (such as ringing a bell or telling the computer to accept a piece of datum).
ASCII is a 7-bit code, but the PC byte is 8 bits. There are 256 (28) possible bit configurations in an 8-bit byte. Hardware and software vendors accept the 128 standard ASCII codes and use the extra 128 bit configurations to represent control characters or noncharacter images to complement their hardware or software product. For example, the IBM-PC version of extended ASCII contains the characters of many foreign languages (such as a [umlaut] and e [acute]) and a wide variety of graphic images that can be combined on a text screen to produce larger images (for example, the box around a window on a display screen).
Microsoft Windows uses the 8-bit ANSI encoding system (developed by the American National Standards /nstitute) to enable the sharing of text between Windows applications. As in IBM, extended ASCII, the first 128 ANSI codes are the same as the ASCII codes, but the next 128 are defined to meet the specific needs of Windows applications.