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Subjects | Fact sheet | Samples
Computing and the Internet: Sample articles
Babbage, Charles (1792–1871)
English mathematician who devised a precursor of the computer. He designed an analytical engine, a general-purpose mechanical computing device for performing different calculations according to a program input on punched cards (an idea borrowed from the Jacquard loom). This device was never built, but it embodied many of the principles on which digital computers are based.
Babbage was born in Totnes, Devon. As a student at Cambridge, he assisted John Herschel with his astronomical calculations and thought they could be better done by machines. His mechanical calculator, or difference engine, begun in 1822, which could compute squares to six places of decimals, got him a commission from the British Admiralty for an expanded version. But this project was abandoned in favour of the analytical engine, on which he worked for the rest of his life. The difference engine could perform only one function, once it was set up. The analytical engine was intended to perform many functions; it was to store numbers and be capable of working to a program. The first computer printer, also designed but never built by Charles Babbage, was completed and put on show at London's Science Museum in April 2000.
Babbage was a founder member of the Royal Astronomical Society, the British Association, the Cambridge Philosophical Society, and the Statistical Society of London. He was elected Fellow of the Royal Society in 1816. His book On the Economy of Machinery and Manufactures (1832) is an analysis of industrial production systems and their economics.
In 1991, the British Science Museum completed Babbage's second difference engine (to demonstrate that it would have been possible with the materials then available). It evaluates polynomials up to the seventh power, with 30-figure accuracy.
byte
Sufficient computer memory to store a single character of data, such as a letter of the alphabet. The character is stored in the byte of memory as a pattern of bits (binary digits), using a code such as ASCII. A byte usually contains eight bits – for example, the capital letter F can be stored as the bit pattern 01000110.
A single byte can specify 256 values, such as the decimal numbers from 0 to 255; in the case of a single-byte pixel (picture element), it can specify 256 different colours. Three bytes (24 bits) can specify 16,777,216 values. Computer memory size is measured in kilobytes (1,024 bytes) or megabytes (1,024 kilobytes).
computer graphics
Use of computers to display and manipulate information in pictorial form. Input may be achieved by scanning an image, by drawing with a mouse or stylus on a graphics tablet, or by drawing directly on the screen with a light pen.
The output may be as simple as a pie chart, or as complex as an animated sequence in a science fiction film, or a seemingly three-dimensional engineering blueprint. The drawing is stored in the computer as raster graphics or vector graphics.
Vector graphics are stored in the computer memory by using geometric formulae. They can be transformed (enlarged, rotated, stretched, and so on) without loss of picture resolution. It is also possible to select and transform any of the components of a vector-graphics display because each is separately defined in the computer memory. In these respects vector graphics are superior to raster graphics. They are typically used for drawing applications, allowing the user to create and modify technical diagrams such as designs for houses or cars.
Raster graphics are stored in the computer memory by using a map to record data (such as colour and intensity) for every pixel that makes up the image. When transformed (enlarged, rotated, stretched, and so on), raster graphics become ragged and suffer loss of picture resolution, unlike vector graphics. They are typically used for painting applications, which allow the user to create artwork on a computer screen much as if they were painting on paper or canvas.
Computer graphics are increasingly used in computer-aided design (CAD), and to generate models and simulations in engineering, meteorology, medicine and surgery, and other fields of science.
Developments in software mean that designers on opposite sides of the world will soon be able to work on complex three-dimensional computer models using ordinary personal computers (PCs) linked by telephone lines rather then powerful graphics workstations.
fuzzy logic
In mathematics and computing, a form of knowledge representation suitable for notions (such as 'hot' or 'loud') that cannot be defined precisely but depend on their context. For example, a jug of water may be described as too hot or too cold, depending on whether it is to be used to wash one's face or to make tea.
The central idea of fuzzy logic is probability of set membership. For instance, referring to someone 175 cm/5 ft 9 in tall, the statement 'this person is tall' (or 'this person is a member of the set of tall people') might be about 70% true if that person is a man, and about 85% true if that person is a woman.
The term 'fuzzy logic' was coined in 1965 by Iranian computer scientist Lofti Zadeh of the University of California at Berkeley,
although the core concepts go back to the work of Polish mathematician Jan Lukasiewicz in the 1920s. It has been largely ignored in Europe and the USA, but was taken up by Japanese manufacturers in the mid-1980s and has since been applied to hundreds of electronic goods and industrial machines. For example, a vacuum cleaner launched in 1992 by Matsushita uses fuzzy logic to adjust its sucking power in response to messages from its sensors about the type of dirt on the floor, its distribution, and its depth. Fuzzy logic enables computerized devices to reason more like humans, responding effectively to complex messages from their control panels and sensors.
optical character recognition
OCR
In computing, a technique for inputting text to a computer by means of a document reader. First, a scanner produces a digital image of the text; then character-recognition software makes use of stored knowledge about the shapes of individual characters to convert the digital image to a set of internal codes that can be stored and processed by a computer.
OCR originally required specially designed characters but current devices can recognize most standard typefaces and even handwriting. OCR is used, for example, by gas and electricity companies to input data collected on meter-reading cards, and by personal digital assistants to recognize users' handwriting.
programming
Writing instructions in a programming language for the control of a computer. Applications programming is for end-user programs, such as accounts programs or word-processing packages. Systems programming is for operating systems and the like, which are concerned more with the internal workings of the computer.
There are several programming styles. Procedural programming, in which programs are written as lists of instructions for the computer to obey in sequence, is by far the most popular. It is the 'natural' style, closely matching the computer's own sequential operation. Declarative programming, as used in the programming language PROLOG, does not describe how to solve a problem, but rather describes the logical structure of the problem. Running such a program is more like proving an assertion than following a procedure. Functional programming is a style based largely on the definition of functions. There are very few functional programming languages, HOPE and ML being the most widely used, though many more conventional languages (for example C) make extensive use of functions. Object-oriented programming, the most recently developed style, involves viewing a program as a collection of objects that behave in certain ways when they are passed certain 'messages'. For example, an object might be defined to represent a table of figures, which will be displayed on screen when a 'display' message is received.
spreadsheet
In computing, a program that mimics a sheet of ruled paper, divided into columns down the page, and rows across. The user enters values into cells within the worksheet, then instructs the program to perform some operation on them, such as totalling a column or finding the average of a series of numbers. Calculations are made by using a formula. Highly complex numerical analyses may be built up from these simple steps.
Columns and rows in a spreadsheet are labelled; although different programs use different methods, columns are often labelled with alpha characters, and rows with numbers. When a cell containing a formula is copied and pasted within a spreadsheet, the formula is said to be relative, meaning the cell references from which it takes its values are relative to its new position. An absolute reference does not change.
The pages of a spreadsheet can be formatted to make them easier to read; the height of rows, the width of columns, and the typeface of the text may all be changed. Number formats may also be changed to display, for example, fractions as decimals or numbers as integers. Spreadsheets are widely used in business for forecasting and financial control. The first spreadsheet program, Software Arts' VisiCalc, appeared in 1979. The best known include Lotus 1-2-3 and Microsoft Excel.
validation
In computing, the process of checking input data to ensure that it is complete, accurate, and reasonable. Although it would be
impossible to guarantee that only valid data are entered into a computer, a suitable combination of validation checks should ensure that most errors are detected.
Common validation checks include:
Character-type check
Each input data item is checked to ensure that it does not contain invalid characters.
For example, an input name might be checked to ensure that it contains only letters of the alphabet, or an input six-figure date might be checked to ensure it contains only numbers.
Field-length check
The number of characters in an input field is checked to ensure that the correct number of characters has been entered. For example, a six-figure date field might be checked to ensure that it does contain exactly six digits.
Control-total check
The arithmetic total of a specific field from a group of records is calculated – for example, the hours worked by a group of employees might be added together – and then input with the data to which it refers. The program recalculates the control total and compares it with the one entered to ensure that entry errors have not been made.
Hash-total check
An otherwise meaningless control total is calculated – for example, by adding together account numbers. Even though the total has no arithmetic meaning, it can still be used to check the validity of the input account numbers.
Parity check
Parity bits are added to binary number codes to ensure that each number in a set of data has the same parity (that each binary number has an even number of 1s, for example). The binary numbers can then be checked to ensure that their parity remains the same. This check is often applied to data after they have been transferred from one part of the computer to another; for example, from a disk drive into the immediate-access memory.
Check digit
A digit is calculated from the digits of a code number and then added to that number as an extra digit. For example, in the ISBN (International Standard Book Number) 0 631 90057 8, the 8 is a check digit calculated from the book code number 063190057 and then added to it to make the full ISBN. When the full code number is input, the computer recalculates the check digit and compares it with the one entered. If the entered and calculated check digits do not match, the computer reports that an entry error of some kind has been made.
Range check
An input numerical data item is checked to ensure that its value falls in a sensible range. For example, an input two-digit day of the month might be checked to ensure that it is in the range 01 to 31.
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