ASCII or American Standard Code for Information Interchange, a set of codes used to represent letters, numbers, a few symbols, and control characters. Originally designed for teletype operations, it has found wide application in computers. A seven-digit (or seven-bit) binary number (see binary system) can represent one of 128 distinct codes. Thus, in decimal equivalents, the series "72, 69, 76, 76, 79" represents the letters "h, e, l, l, o" in ASCII. With the introduction of its personal computer in 1981, the International Business Machines Company (IBM) increased the number of available characters to 256 by using an eight-bit byte. This IBM-extended ASCII set has become a de facto standard. However, the inability of US-ASCII to correctly represent many other languages became an obvious and intolerable misfeature as computer use outside the United States and United Kingdom increased. As a consequence, national extensions to US-ASCII were developed that were incompatible with one another. This in turn led to the standardization of 16-bit (or "double-byte") and 32-byte character sets, such as Unicode, that could accomodate large numbers of linguistic and other symbols.