Data representation

People use computers to work with many kinds of data, including numbers, text, music, photos, and videos. Data representation is the process of transforming this diverse data into form (today digital) that computers can use for processing.

Most computers are digital devices which work with discrete – distinct and separate – data, such as the digits 1 and 0. In contrast, an analog device works with continuous data. As an analogy, a traditional light switch has two discrete states – “on” and “off” – so it is a digital device. A dimmer switch, on the other hand, has a rotating dial that controls a continuous range of brightness. It is, therefore, an analog device. Most computers use the simplest type of digital technology – their circuits have only two possible states. For convenience, let’s say that one of those states is “on” and the other state is “off”. When discussing these states, we usually indicate the “on” state with 1 and the “off” state with 0. These 1s and 0s are referred to as binary digits. It is from this term that we get the word “bit” – bi narydigi t. Computers use sequences of bits to digitally represent numbers, letters, punctuation marks, music, picture, and videos.

Numeric data consists of numbers that might be used in arithmetic operations. Computers represent numeric data using the binary number system, also called “base 2”. The binary number system has only two digits: “0” and “1”. No numeral like “2” exists in this system, so the number “two” is represented in binary as “10” (pronounced “ one zero“). In binary you count 0 (”zero”), 1 (“one”), 10 (“one zero”), instead of counting 0, 1, 2 in decimal. The important point to understand is that the binary number system allows computers to represent virtually any number simply by using 0s and 1s, which conveniently translate into electrical “on” and “off” signals.

Character data is composed of letters, symbols, and numerals that are not used in arithmetic operations. A digital computer uses a series of bits to represent letters, characters, and numerals. Computers employ several types of codes to represent character data, including ASCII, EBCDIC, and Unicode. ASCII (pronounced“ASK ee”, American Standard Code for Information Interchange,) requires only seven bits for each character. ASCII provides codes for 128 characters.

A superset of ASCII, called Extended ASCII, uses eight bits to represent each character. Using eight bits instead of seven bits allowsExtended ASCII to provide codes for 256 characters. Unicode (pronounced ‘YOU ni code’) uses sixteen bits and provides codes for 65,000 characters.

To work with music and pictures, they must be digitized. The term to digitize means to convert raw, analog data into digital format represented by 0s and 1s. A photograph or drawing can be digitized by treating it as a series of colored dots. Each dot is assigned a binary number according to its color. A digital image is simply a list of color numbers for all the dots it contains. In a similar way, music can be digitized by assigning binary codes to notes.

All the “stuff” that your computer works with is stored in files as a long series of 1s and 0s. Your computer needs to know whether to interpret those 1s and 0s as ASCII code, binary numbers, or the code for a picture or sound. To avoid confusion, most computer files contain a file header with information about the code used to represent the file data. A file header can be read by the computer, but never appears on the screen. By reading the header information, a computer can tell how a file’s contents were coded.

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