Business Glossary

popular lines of microcomputers manufactured by IBM. There are many variations of each; this article will mention only the most historically important.

The IBM Personal Computer (PC), introduced in 1981,was the first of a family of very popular microcomputers, including not only IBM products but also "clones" (imitations) made by other companies. The original IBM PC used very little proprietary technology. Thus, it was easy for competitors to build compatible machines without violating patents. See clone; PC compatibility.

IBM maintained a high level of upward compatibility within the PC and PS/2 line. This means that later-model machines would run virtually all software written for earlier models. Nowadays, most PCcompatible computers are made by other companies; IBM continues to market PC-compatibles that are very similar to competitors' products.

IBM's two original machines, the PC and PC XT, are virtually identical, featuring 4.77-MHz 8088 microprocessors with an 8-bit bus. The only difference was that the XT had a 10-megabyte hard disk and had eight expansion slots instead of five. The PC AT, introduced in 1984, was the first PC to use the 80286 microprocessor, enabling programs to run much faster. The PC AT had what is now known as the ISA (Industry Standard Architecture) bus; it accepted both 8-bit (XT-style) and 16-bit plug-in cards.

The PS/2 machines were introduced in 1987 and discontinued in 1995. They were more compact than comparably configured PCs or ATs, and all but the lowest models used the Micro Channel bus, which made it possible in some situations to use more than one CPU in a single machine.

These computers use theASCII character set (see ASCII). In addition, they define printed representations for all character codes from 0 to 255.

Figure 135 shows the printable part of the special character set. Under DOS or at a Windows command prompt, these characters are typed by holding down the Alt key and typing the appropriate number on the numeric keypad at the right side of the keyboard. For example, to type a shaded block, hold down Alt, type 178, and then release Alt.

a font that includes a full set of accented vowels, ligatures, small caps, and other special characters (such as an extended group of case fractions). It is assumed that someone using such a font will have the know-how and the software to be able to set the special characters. Not every typeface has a matching expert set; you may have to take this into consideration when selecting a typeface for a particular job or when purchasing fonts.

the main industrial standardization organization in the United States. There are official ANSI standards in almost all industries, and many of them have to do with computers. In computer programming, ANSI most often refers to one of the following:

1. ANSI standard versions of C, FORTRAN, COBOL, or other programming languages. Typically, a particular manufacturer's version of a language will include all of the features defined in the ANSI standard, plus additional features devised by the manufacturer. To be easily transportable from one computer to another, a program should not use any features that are not in theANSI standard. The programmer can then produce executable versions of it for different types of computers by compiling the same program with different compilers.
2. ANSI standard escape sequences for controlling the screen of a computer terminal or microcomputer. An escape sequence is a series of character codes which, when sent to the screen, causes the screen to do something other than simply display the characters to which the codes correspond. The ANSI escape sequences all begin with theASCII Escape character (code 27). See ANSI screen control.
3. The ANSI extended character set used in MicrosoftWindows, and shown in Table 2. It includes all the ASCII characters plus many others. See ASCII ; IBM PC; Unicode; Windows (Microsoft).

To type any ANSI character in Microsoft Windows, hold down the Alt key while typing 0 followed by the character code number on the numeric keypad at the right-hand side of the keyboard. For example, to type é, hold down Alt and type 0233. You may prefer to use the Character Map utility to select characters and copy them to the Clipboard, and then paste them into your application.

a system for representing characters using up to 20 bits, allowing for 1.048,576 different characters, enough to represent all the written languages of the world, including Japanese and Chinese. This contrasts with the 256 characters possible in ASCII and similar systems.

The Unicode standard is not yet complete. Originally, Unicode characters were 16 bits, as in the UTF-16 format described later, and only 65,536 characters were possible. Unicode version 3 goes beyond this limit and defines over 90,000 characters. Complete information is available at www.unicode.org.

The first 128 Unicode character codes are the same as ASCII, including end-of-line marks (see CRLF). In various programming languages and editors, Unicode character codes are written as U+XXXX or \uXXXX, where XXXX stands for a series of hexadecimal digits; thus, the letter A, ASCII hexadecimal 41, is Unicode U+0041. Figure 283 shows examples of Unicode characters.

There are several kinds of Unicode text files. The most important are:

• UTF-8 – Same as ASCII for codes up to 127; thus, a UTF-8 file can also be anASCII file. Higher-numbered codes are represented by sequences of up to 4 bytes.
• UTF-16 big-endian – Each character occupies 2 bytes (16 bits), high-order byte first. The file begins with hexadecimal FE FF or with any Unicode character. Codes higher than 16 bits are represented by pairs of 16-bit sequences.
• UTF-16 little-endian – Just like UTF-16 big-endian, except that each pair of bytes has the low-order byte first, and the file begins with hexadecimal FF FE (representing the value FEFF). This is the Unicode system normally used in Microsoft Windows.

Unicode is used internally by the Java programming language and many newer software packages. However, the characters that you will actually see on your machine are limited by the fonts installed.

Hint: When you open a UTF-16 file in an ASCII text editor on a PC, you generally see characters separated by blanks ("l i k e t h i s"- the blanks are really ASCII 0). The remedy is to use a Unicode editor, such asWindows Notepad, and save the file as ASCII.