The definitions below came from www.pcwebopedia.com (an on-line dictionary of computer terms).

Array: In programming, a series of objects all of which are the same size and type. Each object in an array is called an array element. For example, you could have an array of integers or an array of characters or an array of anything that has a defined data type. The important characteristics of an array are:

Each element has the same data type (although they may have different values).

The entire array is stored contiguously in memory (that is, there are no gaps between elements).

Arrays can have more than one dimension. A one-dimensional array is called a vector ; a two-dimensional array is called a matrix.

ASCII: Acronym for the American Standard Code for Information Interchange. Pronounced ask-ee, ASCII is a code for representing English characters as numbers, with each letter assigned a number from 0 to 127. For example, the ASCII code for uppercase M is 77. Most computers use ASCII codes to represent text, which makes it possible to transfer data from one computer to another.

Text files stored in ASCII format are sometimes called ASCII files. Text editors and word processors are usually capable of storing data in ASCII format, although ASCII format is not always the default storage format. Most data files, particularly if they contain numeric data, are not stored in ASCII format. Executable programs are never stored in ASCII format.

The standard ASCII character set uses just 7 bits for each character. There are several larger character sets that use 8 bits, which gives them 128 additional characters. The extra characters are used to represent non-English characters, graphics symbols, and mathematical symbols. Several companies and organizations have proposed extensions for these 128 characters. The DOS operating system uses a superset of ASCII called extended ASCII or high ASCII. A more universal standard is the ISO Latin 1 set of characters, which is used by many operating systems, as well as Web browsers.

Another set of codes that is used on large IBM computers is EBCDIC.

Byte: Abbreviation for binary term, a unit of storage capable of holding a single character. On almost all modern computers, a byte is equal to 8 bits. Large amounts of memory are indicated in terms of kilobytes (1,024 bytes), megabytes (1,048,576 bytes), and gigabytes (1,073,741,824 bytes). A disk that can hold 1.44 megabytes, for example, is capable of storing approximately 1.4 million characters, or about 3,000 pages of information.

Character: In computer software, any symbol that requires one byte of storage. This includes all the ASCII and extended ASCII characters, including the space character. In character-based software, everything that appears on the screen, including graphics symbols, is considered to be a character. In graphics-based applications, the term character is generally reserved for letters, numbers, and punctuation.

Character String: A series of characters manipulated as a group. A character string differs from a name in that it does not represent anything -- a name stands for some other object.

Enclosing the characters in single or double quotes often specifies a character string. For example, WASHINGTON would be a name, but 'WASHINGTON' and "WASHINGTON" would be character strings.

The length of a character string is usually the number of characters in it. For example, the character string "WASHINGTON" has a length of 10 (the quote marks are not included). Some programs, however, mark the beginning or end of a character string with an invisible character, so the length might actually be one greater than the number of characters.

Data Type: In programming, classification of a particular type of information. It is easy for humans to distinguish between different types of data. We can usually tell at a glance whether a number is a percentage, a time, or an amount of money. We do this through special symbols -- %, :, and $ -- that indicate the data's type. Similarly, a computer uses special internal codes to keep track of the different types of data it processes.

Most programming languages require the programmer to declare the data type of every data object, and most database systems require the user to specify the type of each data field. The available data types vary from one programming language to another, and from one database application to another, but the following usually exist in one form or another:

integer : In more common parlance, whole number; a number that has no fractional part.

floating-point : A number with a decimal point. For example, 3 is an integer, but 3.5 is a floating-point number.

character (text ): Readable text

Extended ASCII: A set of codes that extends the basic ASCII set. The basic ASCII set uses 7 bits for each character, giving it a total of 128 unique symbols. The extended ASCII character set uses 8 bits, which gives it an additional 128 characters. The extra characters represent characters from foreign languages and special symbols for drawing pictures.

	3.0
	-111.5
	½
	3E-5

The last example is a computer shorthand for scientific notation. It means 3*10-5 (or 10 to the negative 5th power multiplied by 3).

In essence, computers are integer machines and are capable of representing real numbers only by using complex codes. The most popular code for representing real numbers is called the IEEE Floating-Point Standard .

The term floating point is derived from the fact that there is no fixed number of digits before and after the decimal point; that is, the decimal point can float. There are also representations in which the number of digits before and after the decimal point is set, called fixed-point representations. In general, floating-point representations are slower and less accurate than fixed-point representations, but they can handle a larger range of numbers.

Note that most floating-point numbers a computer can represent are just approximations. One of the challenges in programming with floating-point values is ensuring that the approximations lead to reasonable results. If the programmer is not careful, small discrepancies in the approximations can snowball to the point where the final results become meaningless.

Because mathematics with floating-point numbers requires a great deal of computing power, many microprocessors come with a chip, called a floating point unit (FPU ), specialized for performing floating-point arithmetic. FPUs are also called math coprocessors and numeric coprocessors.

	0
	1
	-125
	144457

In contrast, the following are not integers:

	5.34
	-1.0
	1.3E4
	"string"

The first three are floating-point numbers; the last is a character string.

Integers, floating-point numbers, and character strings constitute the basic data types that most computers support. There are often different sizes of integers available; for example, PCs support short integers, which are 2 bytes, and long integers, which are 4 bytes.

Matrix: (1) A two-dimensional array; that is, an array of rows and columns.

(2) The background area of color display.

Vector: 1) In computer programming, a one-dimensional array. A vector can also mean a pointer.

(2) In computer graphics, a line that is defined by its start and end point.