Arithmetic/logic unit (alu)

The ALU is capable of performing two classes of operations: arithmetic and logic.

The set of arithmetic operations that a particular ALU supports may be limited to adding and subtracting or might include multiplying or dividing, trigonometry functions (sine, cosine, etc) and square roots. Some can only operate on whole numbers (integers) whilst others use floating point to represent real numbers—albeit with limited precision. However, any computer that is capable of performing just the simplest operations can be programmed to break down the more complex operations into simple steps that it can perform. Therefore, any computer can be programmed to perform any arithmetic operation—although it will take more time to do so if its ALU does not directly support the operation. An ALU may also compare numbers and return Boolean truth values (true or false) depending on whether one is equal to, greater than or less than the other ("is 64 greater than 65?").

Logic operations involve Boolean logic: AND, OR, XOR and NOT. These can be useful both for creating complicated conditional statements and processing Boolean logic.

Superscalar computers contain multiple ALUs so that they can process several instructions at the same time. Graphics processors and computers with SIMD and MIMD features often provide ALUs that can perform arithmetic on vectors and matrices.

Bits for pictures

Each tiny dot on the computer screen is called a picture element or pixel. Images and texts are formed by combining a large number of pixels. In a bit-mapped display the dots displayed on the screen correspond, pixel by pixel, with bits in the main memory on the computer. The bits are held in an area of the memory called the “refresh buffer” and are stored in groups that represent the horizontal and vertical position of the pixels on the screen and whether the pixels are “on” or “off”.

On monochrome systems, one bit in this “map” represents one pixel on the screen and can be either “on” or “off” (black or white).

On color systems each pixels is a certain combination of the three primary colors: red, green and blue. The total number of colors which can be shown on the screen is called the color palette. The size of this palette depends on the graphic adaptor a separate video card that converts the bits into visual signals. A graphic adaptor with 1 bit per primary color can generate up to 8 colors. A graphic adaptor with 8 bits per primary color can generate 16.7 million colors.

The internet

The Internet is international computer network linking together thousands of individual networks at military and government agencies, educational institutions, nonprofit organizations, industrial and Financial corporations of all sizes, and commercial enterprises (called gateways or service providers) that enable individuals to access the network. The most popular features of the Internet include electronic mail (e-mail), discussion groups (called newsgroups or bulletin boards, where users can post messages and look for responses on a system called Usenet), on-line conversations (called chats), adventure and role-playing games, information retrieval, and electronic commerce (e-commerce).

The public information stored in the multitude of computer networks connected to the Internet forms a huge electronic library, but the enormous quantity of data and number of linked computer networks also make it difficult to find where the desired information resides and then to retrieve it. A number of progressively easier-to-use interfaces and tools have been developed to facilitate searching. Among these are search engines, such as Archie, Gopher, and WAIS (Wide Area Information Server), and a number of commercial indexes, which are programs that use a proprietary algorithm to search a large collection of documents for keywords and return a list of documents containing one or more of the keywords.

There is also such a program as Telnet that allows users of one computer to connect with another, distant computer in a different network. The File Transfer Protocol (FTP) is used to transfer information between computers in different networks. The greatest impetus to the popularization of the Internet came with the introduction of the World Wide Web (WWW), a hypertext system that makes

MOUSE

In computing, a mouse (plural mice, mouse devices, or mouses) is a pointing device that functions by detecting two-dimensional motion relative to its supporting surface. Physically, a mouse consists of a small case, held under one of the user's hands, with one or more buttons. It sometimes features other elements, such as "wheels", which allow the user to perform various system-dependent operations, or extra buttons or features can add more control or dimensional input. The mouse's motion typically translates into the motion of a pointer on a display, which allows for fine control of a Graphical User Interface.

The name mouse, originated at the Stanford Research Institute, derives from the resemblance of early models (which had a cord attached to the rear part of the device, suggesting the idea of a tail) to the common mouse.

The first marketed integrated mouse — shipped as a part of a computer and intended for personal computer navigation — came with the Xerox 8010 Star Information System in 1981.