Computer Concepts

Basic Computer Concepts

Khalil A.Channa

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What is Computer ? Hard Ware Software Khalil A.Channa

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Basic Concepts of Computer Hardware Primary Memory

Input Units

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CPU (Central Processing Unit)

Output Units

This model of the typical digital computer is often called the von Neumann computer. • Programs and data are stored in the same memory: primary memory. • The computer can only perform one instruction at a time. Khalil A.Channa

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Basic Concepts of Computer Hardware ■

Input/Output (I/O): Refers to the process of getting information into and out of the computer. • Input: Those parts of the computer receiving information to programs. • Output: Those parts of the computer that provide results of computation to the person using the computer.

Khalil A.Channa

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Sources of Data for the Computer ■

Two types of data stored within a computer: • Original data or information: Data being introduced to a computing system for the first time. – Computers can deal directly with printed text, pictures, sound, and other common types of information. • Previously stored data or information: Data that has already been processed by a computer and is being stored for later use. – These are forms of binary data useful only to the computer. – Examples: Floppy disks, DVD disks, and music CDs.

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Input Devices ■

Two categories of input hardware: • Those that deal with original data. • Those that handle previously stored data.

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Input Devices ■

Input hardware: Those that deal with original data. • • • • •

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Keyboard Mouse Voice recognition hardware Scanner Digital camera

Digitizing: The process of taking a visual image, or audio recording and converting it to a binary form for the computer. • Used as data for programs to display, play or manipulate the digitized data. Khalil A.Channa

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Input Devices ■

Connecting Hardware to the computer: • Hardware needs access through some general input/output connection. – Port: The pathway for data to go into and out of the computer from external devices such as keyboards. • There are many standard ports as well as custom electronic ports designed for special purposes. • Ports follow standards that define their use. » SCSI, USB: Multiple peripheral devices (chain). » RS-232, IDE: Individual peripheral devices. – Peripheral device: A piece of hardware like a printer or disk drive, that is outside the main computer. Khalil A.Channa

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Input Devices ■

Connecting Hardware to the computer: (continued) • Hardware needs software on the computer that can service the device. – Device driver: Software addition to the operating system that will allow the computer to communicate with a particular device.

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Input Devices ■

Common Basic Technologies for Storing Binary Information: • Electronic • Magnetic • Optical

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Input Devices ■

Electronic Circuits • Most expensive of the three forms for storing binary information. • A flip-flop circuit has either one electronic status or the other. It is said to flip-flop from one to the other. • Electronic circuits come in two forms: – Permanent – Non-permanent

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Input Devices ■

Magnetic Technology • Two parts to most of the magnetic forms of information storage: – The medium that stores the magnetic information. • Example: Floppy disk. Tiny spots on the disk are magnetized to represent 0s and 1s. – The device that can “read” that information from the medium. • The drive spins the disk. • It has a magnetic sensing arm that moves over the disk. • Performs nondestructive reading. Khalil A.Channa

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Input Devices ■

Optical • Uses lasers to “read” the binary information from the medium, usually a disc. – Millions of tiny holes are “burned” into the surface of the disc. – The holes are interpreted as 1s. The absence of holes are interpreted as 0s.

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Input Devices ■

Secondary Memory Input Devices • These input devices are used by a computer to store information and then to retrieve that information as needed. – External to the computer. – Commonly consists of floppy disks, hard disk drives, or CD-ROMs. • Secondary memory uses binary. – The usual measurement is the byte. • A byte consists of 8 binary digits (bits). The byte is a standard unit.

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Input Devices ■

The four most important characteristics of storage devices: • • • •

Speed and access time Cost / Removable versus non-removable Capacity Type of access

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Input Devices ■

Speed (Access time) - How fast information can be taken from or stored onto the computer memory device’s medium. • Electronic circuits: Fastest to access. – 40 billionths of a second. • Floppy disks: Very slow in comparison. – Takes up to 1/2 second to reach full speed before access is even possible.

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Input Devices ■

Cost • Megabyte: A Million bytes. • Gigabyte: A billion bytes. • Two parts to a removable secondary storage device: – The cost of the medium. (Cheaper if bought in quantity) – The cost of the drive. Examples: Cost for drive Cost for medium Floppy drive (1.4MB) 59.00 .50 Zip 100 (100 MB) 99.00 10.00 CD-WR (650 MB) 360.00 and up 1.00 Khalil A.Channa

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Input Devices ■

Capacity - The amount of information that can be stored on the medium. Unit 1 bit 1 nibble 1 byte 1 kilobyte 1 megabyte 1 gigabyte 1 terabyte

Description 1 binary digit 4 bits 8 bits 1,024 bytes 1,048,576 bytes 1 million bytes 1,073,741,824 bytes 1 billion bytes 1 trillion bytes Khalil A.Channa

Approximate Size

1 character ≈1/2 page, double spaced ≈500,000 pages ≈5 million pages ≈5 billion pages 3-18

Input Devices ■

Type of Access – Sequential - Obtained by proceeding through the storage medium from the beginning until the designated area is reached (as in magnetic tape). – Random Access - Direct access (as in floppy and hard disks).

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Primary Memory ■

Primary storage or memory: Is where the data and program that are currently in operation or being accessed are stored during use. • Consists of electronic circuits: Extremely fast and expensive. • Two types: – RAM (non-permanent) • Programs and data can be stored here for the computer’s use. • Volatile: All information will be lost once the computer shuts down. – ROM (permanent) • Contents do not change. Khalil A.Channa

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The Central Processing Unit ■

The Central Processing Unit ( CPU) • Often referred to as the “brain” of the computer. • Responsible for controlling all activities of the computer system. • The three major components of the CPU are: 1. Arithmetic Unit (Computations performed) Accumulator (Results of computations kept here) 2. Control Unit (Has two locations where numbers are kept) Instruction Register (Instruction placed here for analysis) Program Counter (Which instruction will be performed next?) 3. Instruction Decoding Unit (Decodes the instruction)

• Motherboard: The place where most of the electronics including the CPU are mounted. Khalil A.Channa

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Output Devices ■

Output units store and display information (calculated results and other messages) for us to see and use. • Floppy disk drives and Hard disk drives. • Display monitors: Hi-resolution monitors come in two types: – Cathode ray tube (CRT) - Streams of electrons make phosphors glow on a large vacuum tube. – Liquid crystal display (LCD) - A flat panel display that uses crystals to let varying amounts of different colored light to pass through it. • Developed primarily for portable computers.

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Output Devices ■

Audio Output Devices • Windows machines need special audio card for audio output. • Macintosh has audio playback built in. • Audio output is useful for: – Music • CD player is a computer. • Most personal computers have CD players that can access both music CDs and CD-ROMs. – Voice synthesis (becoming more human sounding.) – Multimedia – Specialized tasks (i.e.: elevator’s floor announcements) Khalil A.Channa

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Output Devices ■

Optical Disks: CD-ROM and DVD • CD-ROM (Compact Disk - Read Only Memory) – By its definition, CD-ROM is Read Only. – Special CD drives “burn” information into blank CDs. • Burn: A laser is used to “burn” craters into the surface to represent a binary 1. • Two main types of CDs: » CD-R (Compact Disk - Recordable) » CD-WR (Compact Disk - ReWritable) – It takes longer to write to a CD-R than a hard drive. – Special software is needed to record. Khalil A.Channa

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Output Devices ■

DVD (Digital Versatile Disk) • Allows up to 17 gigabytes of storage (from 4.7 GB to 17 GB). • Compatible with older CD-ROM technology. • The four versions of the DVD:

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Output Devices ■

Storage Requirements: How much storage capacity is needed for… • • • • •

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One keystroke on a keyboard. One page single-spaced document. Nineteen pages formatted text. One second of high-fidelity sound. Complete word processing program.

1 byte (8 bits) 4.0 K 75 K 95-110 K 8.4 MG

Storage Capacity: How much data can be stored on… • • • •

One inch of 1/2 in. wide magnetic tape. One 3 1/2” floppy disk, high density. One Compact Disk. One DVD. Khalil A.Channa

4K 1.4 MG 650 MG up to 17 GB

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Moving Information Within the Computer ■

How do binary numerals move into, out of, and within the computer? • Information is moved about in bytes, or multiple bytes called words. – Words are the fundamental units of information. – The number of bits per word may vary per computer. – A word length for most large IBM computers is 32 bits:

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Moving Information Within the Computer ■

Bits that compose a word are passed in parallel from place to place. • Ribbon cables: – Consist of several wires, molded together. – One wire for each bit of the word or byte. – Additional wires coordinate the activity of moving information. – Each wire sends information in the form of a voltage pulse. Khalil A.Channa

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Moving Information Within the Computer ■

Example of sending the word WOW over the ribbon cable • Voltage pulses corresponding to the ASCII codes would pass through the cable.

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Packaging the Computer Fast Expensive Complex Large ■

The many physical forms of the general purpose computer: • All follow general organization: – Primary memory – Input units – Output units – Central Processing Unit • Grouped according to speed, cost, size, and complexity.

Super Computers Mainframe Computers Minicomputers Microcomputer Palmtop Computer Calculator Slow Cheap Simple Small

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Software Tools for Maintaining Your Computer Hardware ■

Utility Programs exist that can help diagnose and solve computer hardware problems. • Four major problem areas where utility programs are helpful: – Finding and fixing problems. • Testing Input/Output peripherals. • Testing RAM, motherboard, video cards. • Recovering deleted files or fixing damaged disks.

– Improving computer performance. • De-fragmenting a disk (Packs all files closer together).

– Preventative maintenance. – Troubleshooting. • Locates incompatible programs. Khalil A.Channa

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What is an Operating System? ■

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A program that acts as an intermediary between a user of a computer and the computer hardware. Operating system goals: • Execute user programs and make solving user problems easier. • Make the computer system convenient to use.

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Use the computer hardware in an efficient manner.

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Computer System Structure ■

Computer system can be divided into four components • Hardware – provides basic computing resources – CPU, memory, I/O devices • Operating system – Controls and coordinates use of hardware among various applications and users • Application programs – define the ways in which the system resources are used to solve the computing problems of the users – Word processors, compilers, web browsers, database systems, video games • Users – People, machines, other computers Khalil A.Channa

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Four Components of a Computer System

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Operating System Definition ■

OS is a resource allocator • Manages all resources • Decides between conflicting requests for efficient and fair resource use

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OS is a control program • Controls execution of programs to prevent errors and improper use of the computer

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Operating System Definition (Cont.) ■ ■

No universally accepted definition “Everything a vendor ships when you order an operating system” is good approximation • But varies wildly

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“The one program running at all times on the computer” is the kernel. Everything else is either a system program (ships with the operating system) or an application program

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Computer Startup ■

bootstrap program is loaded at power-up or reboot • Typically stored in ROM or EPROM, generally known as firmware • Initializates all aspects of system • Loads operating system kernel and starts execution

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I/O Structure ■

After I/O starts, control returns to user program only upon I/O completion. • Wait instruction idles the CPU until the next interrupt • Wait loop (contention for memory access). • At most one I/O request is outstanding at a time, no simultaneous I/O processing.

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After I/O starts, control returns to user program without waiting for I/O completion. • System call – request to the operating system to allow user to wait for I/O completion. • Device-status table contains entry for each I/O device indicating its type, address, and state. • Operating system indexes into I/O device table to determine device status and to modify table entry to include interrupt. Khalil A.Channa

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Direct Memory Access Structure ■

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Used for high-speed I/O devices able to transmit information at close to memory speeds. Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention. Only one interrupt is generated per block, rather than the one interrupt per byte.

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Storage Structure ■

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Main memory – only large storage media that the CPU can access directly. Secondary storage – extension of main memory that provides large nonvolatile storage capacity. Magnetic disks – rigid metal or glass platters covered with magnetic recording material • Disk surface is logically divided into tracks, which are subdivided into sectors. • The disk controller determines the logical interaction between the device and the computer. Khalil A.Channa

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Storage Hierarchy ■

Storage systems organized in hierarchy. • Speed • Cost • Volatility

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Caching – copying information into faster storage system; main memory can be viewed as a last cache for secondary storage.

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Storage-Device Hierarchy

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Caching ■

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Important principle, performed at many levels in a computer (in hardware, operating system, software) Information in use copied from slower to faster storage temporarily Faster storage (cache) checked first to determine if information is there • If it is, information used directly from the cache (fast) • If not, data copied to cache and used there

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Cache smaller than storage being cached • Cache management important design problem • Cache size and replacement policy Khalil A.Channa

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Operating System Structure ■

Multiprogramming needed for efficiency • Single user cannot keep CPU and I/O devices busy at all times • Multiprogramming organizes jobs (code and data) so CPU always has one to execute • A subset of total jobs in system is kept in memory • One job selected and run via job scheduling • When it has to wait (for I/O for example), OS switches to another job

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Timesharing (multitasking) is logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing • • • •

Response time should be < 1 second Each user has at least one program executing in memory process If several jobs ready to run at the same time CPU scheduling If processes don’t fit in memory, swapping moves them in and out to run • Virtual memory allows execution of processes not completely in memory Khalil A.Channa

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Applet ■

A small Java application that is downloaded by an ActiveX or Java-enabled web browser. Once it has been downloaded, the applet will run on the user's computer. Common applets include financial calculators and web drawing programs.

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ASCII ■

American Standard Code for Information Interchange, an encoding system for converting keyboard characters and instructions into the binary number code that the computer understands.

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Bandwidth ■

The capacity of a networked connection. Bandwidth determines how much data can be sent along the networked wires. Bandwidth is particularly important for Internet connections, since greater bandwidth also means faster downloads.

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Boot ■

To start up a computer. Cold boot—restarting computer after having turned off the power. Warm boot—restarting computer without having turned off the power.

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Browser ■

Software used to navigate the Internet. Netscape Navigator and Microsoft Internet Explorer are today's most popular browsers for accessing the World Wide Web.

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Chat ■

Typing text into a message box on a screen to engage in dialog with one or more people via the Internet or other network.

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chip • A tiny wafer of silicon containing miniature electric circuits that can store millions of bits of information.

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client • A single user of a network application that is operated from a server. A client/server architecture allows many people to use the same data simultaneously. The program's main component (the data) resides on a centralized server, with smaller components (user interface) on each client.

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Cookie ■

A text file sent by a Web server that is stored on the hard drive of a computer and relays back to the Web server things about the user, his or her computer, and/or his or her computer activities

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cracker • A person who “breaks in” to a computer through a network, without authorization and with mischievous or destructive intent (a crime in some states).

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crash • A hardware or software problem that causes information to be lost or the computer to malfunction. Sometimes a crash can cause permanent damage to a computer.

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cursor • A moving position-indicator displayed on a computer monitor that shows a computer operator where the next action or operation will take place.

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cyberspace • Slang for the Internet.

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database – A collection of similar information stored in a file, such as a database of addresses. This information may be created and stored in a database management system (DBMS).

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debug • Slang. To find and correct equipment defects or program malfunctions.

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default • The pre-defined configuration of a system or an application. In most programs, the defaults can be changed to reflect personal preferences.

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desktop • The main directory of the user interface. Desktops usually contain icons that represent links to the hard drive, a network (if there is one), and a trash or recycling can for files to be deleted. It can also display icons of frequently used applications, as requested by the user.

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desktop publishing • The production of publication-quality documents using a personal computer in combination with text, graphics, and page layout programs.

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directory • A list of files stored in the computer. Khalil A.Channa

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domain • Represents an IP (Internet Protocol) address or set of IP addresses that comprise a domain. The domain name appears in URLs to identify web pages or in email addresses. For example, the email address for the First Lady is [email protected], “whitehouse.gov” being the domain name. Each domain name ends with a suffix that indicates what “top level domain” it belongs to. These are: “.com” for commercial, “.gov” for government, “.org” for organization, “.edu” for educational institution, “.biz” for business, “.info” for information, “.tv” for television, “.ws” for website. Domain suffixes may also indicate the country in which the domain is registered. No two parties can ever hold the same domain name.

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domain name • The name of a network or computer linked to the Internet. Domains are defined by a common IP address or set of similar IP (Internet Protocol) addresses. Khalil A.Channa

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download • The process of transferring information from a web site (or other remote location on a network) to the computer. It is possible to “download a file” or “view a download.”

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DOS • Disk Operating System. An operating system designed for early IBM-compatible PCs.

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Drop-down menu • A menu window that opens vertically on-screen to display context-related options. Also called pop-up menu or pull-down menu.

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DSL • Digital Subscriber Line. A method of connecting to the Internet via a phone line. A DSL connection uses copper telephone lines but is able to relay data at much higher speeds than modems and does not interfere with telephone use.

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DVD • Digital Video Disc—Similar to a CD-ROM, it stores and plays both audio and video.

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ebook • An electronic (usually hand-held) reading device that allows a person to view digitally stored reading materials.

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email • Electronic mail; messages, including memos or letters, sent electronically between networked computers that may be across the office Khalil A.Channa

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encryption • The process of transmitting scrambled data so that only authorized recipients can unscramble it. For instance, encryption is used to scramble credit card information when purchases are made over the Internet.

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ethernet • A type of network.

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ethernet card • A board inside a computer to which a network cable can be attached.

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file • A set of data that is stored in the computer.

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firewall • A set of security programs that protect a computer from outside interference or access via the Internet.

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Firewire • Apple® Computer's high-speed data transfer. Frequently used to import video to a computer.

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folder • A structure for containing electronic files. In some operating systems, it is called a “directory.”

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fonts • Sets of typefaces (or characters) that come in different styles and sizes.

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freeware • Software created by people who are willing to give it away for the satisfaction of sharing or knowing they helped to simplify other people's lives. It may be freestanding software, or it may add functionality to existing software.

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FTP • File Transfer Protocol. A format and set of rules for transferring files from a host to a remote computer.

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gigabyte (GB) • 1024 megabytes. Also called gig. Khalil A.Channa

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glitch • The cause of an unexpected malfunction.

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Gopher • An Internet search tool that allows users to access textual information through a series of menus, or if using FTP, through downloads.

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GUI • Graphical User Interface. A system that simplifies selecting computer commands by enabling the user to point to symbols or illustrations (called icons) on the computer screen with a mouse.

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groupware • Software that allows networked individuals to form groups and collaborate on documents, programs, or databases.

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hacker • A person with technical expertise who experiments with computer systems to determine how to develop additional features. Hackers are occasionally requested by system administrators to try and “break into” systems via a network to test security. The term hacker is sometimes incorrectly used interchangeably with cracker. A hacker is called a “white hat” and a cracker a “black hat.” Khalil A.Channa

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hard copy • A paper printout of what you have prepared on the computer.

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hard drive • another name for the hard disc that stores information information in a computer.

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home page • The main page of a Web site used to greet visitors, provide information about the site, or to direct the viewer to other pages on the site.

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HTML • Hypertext Markup Language. A standard of text markup conventions used for documents on the World Wide Web. Browsers interpret the codes to give the text structure and formatting (such as bold, blue, or italic).

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HTTP • Hypertext Transfer Protocol. A common system used to request and send HTML documents on the World Wide Web. It is the first portion of all URL addresses on the World Wide Web (e.g., http://www.whitehouse.gov). Khalil A.Channa

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HTTPS • Hypertext Transfer Protocol Secure. Often used in intracompany internet sites. Passwords are required to gain access.

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hyperlink • Text or an image that is connected by hypertext coding to a different location. By selecting the text or image with a mouse, the computer “jumps to” (or displays) the linked text.

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hypermedia • Integrates audio, graphics, and/or video through links embedded in the main program.

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hypertext • A system for organizing text through links, as opposed to a menudriven hierarchy such as Gopher. Most Web pages include hypertext links to other pages at that site, or to other sites on the World Wide Web. Khalil A.Channa

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Internet • An international conglomeration of interconnected computer networks. Begun in the late 1960s, it was developed in the 1970s to allow government and university researchers to share information. The Internet is not controlled by any single group or organization. Its original focus was research and communications, but it continues to expand, offering a wide array of resources for business and home users.

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IP (Internet Protocol) address • An Internet Protocol address is a unique set of numbers used to locate another computer on a network. The format of an IP address is a 32-bit string of four numbers separated by periods. Each number can be from 0 to 255 (i.e., 1.154.10.266). Within a closed network IP addresses may be assigned at random, however, IP addresses of web servers must be registered to avoid duplicates.

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Java • An object-oriented programming language designed specifically for programs (particularly multimedia) to be used over the Internet. Java allows programmers to create small programs or applications (applets) to enhance Web sites.

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Javascript/ECMA script • A programming language used almost exclusively to manipulate content on a web page. Common Javascript functions include validating forms on a web page, creating dynamic page navigation menus, and image rollovers. Khalil A.Channa

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Linux • A UNIX®-like, open-source operating system developed primarily by Linus Torvalds. Linux is free and runs on many platforms, including both PCs and Macintoshes. Linux is an open-source operating system, meaning that the source code of the operating system is freely available to the public. Programmers may redistribute and modify the code, as long as they don't collect royalties on their work or deny access to their code. Since development is not restricted to a single corporation more programmers can debug and improve the source code faster..

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Megabyte (MB) • Equal to 1,048,576 bytes, usually rounded off to one million bytes (also called a “meg”).

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Memory • Temporary storage for information, including applications and documents. The information must be stored to a permanent device, such as a hard disc or CD-ROM before the power is turned off, or the information will be lost. Computer memory is measured in terms of the amount of information it can store, commonly in megabytes or gigabytes. Khalil A.Channa

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Menu • A context-related list of options that users can choose from.

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Menu bar • The horizontal strip across the top of an application's window. Each word on the strip has a context sensitive drop-down menu containing features and actions that are available for the application in use.

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Merge • To combine two or more files into a single file.

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MHz • An abbreviation for Megahertz, or one million hertz. One MHz represents one million clock cycles per second and is the measure of a computer microprocessor's speed. For example, a microprocessor that runs at 300 MHz executes 300 million cycles per second. Each instruction a computer receives takes a fixed number of clock cycles to carry out, therefore the more cycles a computer can execute per second, the faster its programs run. Megahertz is also a unit of measure for bandwidth.

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Modem • A device that connects two computers together over a telephone or cable line by converting the computer's data into an audio signal. Modem is a contraction for the process it performs: modulate-demodulate.

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Monitor • A video display terminal.

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Mouse • A small hand-held device, similar to a trackball, used to control the position of the cursor on the video display; movements of the mouse on a desktop correspond to movements of the cursor on the screen.

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MP3 • Compact audio and video file format. The small size of the files makes them easy to download and e-mail. Format used in portable playback devices.

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multimedia • Software programs that combine text and graphics with sound, video, and animation. A multimedia PC contains the hardware to support these capabilities.

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MS-DOS • An early operating system developed by Microsoft Corporation (Microsoft Disc Operating System).

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network • A system of interconnected computers.

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palm • A hand-held computer.

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PDA Personal Digital Assistant. A hand-held computer that can store daily appointments, phone numbers, addresses, and other important information. Most PDAs link to a desktop or laptop computer to download or upload information.

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PDF • Portable Document Format. A format presented by Adobe Acrobat that allows documents to be shared over a variety of operating systems. Documents can contain words and pictures and be formatted to have electronic links to other parts of the document or to places on the web.

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Pentium chip • Intel's fifth generation of sophisticated high-speed microprocessors. Pentium means “the fifth element.”

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peripheral) • Any external device attached to a computer to enhance operation. Examples include external hard drive, scanner, printer, speakers, keyboard, mouse, trackball, stylus and tablet, and joystick.

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personal computer (PC) • A single-user computer containing a central processing unit (CPU) and one or more memory circuits. Khalil A.Channa

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petabyte • A measure of memory or storage capacity and is approximately a thousand terabytes.

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petaflop • A theoretical measure of a computer's speed and can be expressed as a thousand-trillion floating-point operations per second.

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platform • The operating system, such as UNIX®, Macintosh®, Windows®, on which a computer is based.

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plug and play • Computer hardware or peripherals that come set up with necessary software so that when attached to a computer, they are “recognized” by the computer and are ready to Khalil A.Channa 3-73 use.

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pop-up menu • A menu window that opens vertically or horizontally on-screen to display context-related options. Also called drop-down menu or pull-down menu.

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printer • A mechanical device for printing a computer's output on paper. There are three major types of printers:

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Dot matrix: creates individual letters, made up of a series of tiny ink dots, by punching a ribbon with the ends of tiny wires. (This type of printer is most often used in industrial settings, such as direct mail for labeling.) Ink jet: sprays tiny droplets of ink particles onto paper. Laser: uses a beam of light to reproduce the image of each page using a magnetic charge that attracts dry toner that is transferred to paper and sealed with heat.

program • A precise series of instructions written in a computer language that tells the computer what to do and how to do it. Programs are also called “software” or “applications.” Khalil A.Channa

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programming language • A series of instructions written by a programmer according to a given set of rules or conventions (“syntax”). High-level programming languages are independent of the device on which the application (or program) will eventually run; low-level languages are specific to each program or platform. Programming language instructions are converted into programs in language specific to a particular machine or operating system (“machine language”) so that the computer can interpret and carry out the instructions. Some common programming languages are BASIC, C, C++, dBASE, FORTRAN, and Perl.

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pull-down menu • A menu window that opens vertically on-screen to display context-related options. Also called drop-down menu or pop-up menu.

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push technology • Internet tool that delivers specific information directly to a user's desktop, eliminating the need to surf for it. PointCast, which delivers news in user-defined categories, is a popular example of this technology.

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QuickTime® • Audio-visual software that allows movie-delivery via the Internet and e-mail. QuickTime mages are viewed on a monitor. Khalil A.Channa

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search engine • Software that makes it possible to look for and retrieve material on the Internet, particularly the Web. Some popular search engines are Alta Vista, Google, HotBot, Yahoo!, Web Crawler, and Lycos.

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server • A computer that shares its resources and information with other computers, called clients, on a network.

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shareware • Software created by people who are willing to sell it at low cost or no cost for the gratification of sharing. It may be freestanding software, or it may add functionality to existing software.

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spider • A process search engines use to investigate new pages on a web site and collect the information that needs to be put in their indices.

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spreadsheet • Software that allows one to calculate numbers in a format that is similar to pages in a conventional ledger. Khalil A.Channa

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UNIX® •

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upload •

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Uniform Resource Locator.

1. The protocol for identifying a document on the Web. 2. A Web address (e.g., www.census.gov). A URL is unique to each user. See also domain. UPS •

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The process of transferring information from a computer to a web site (or other remote location on a network).

v. To transfer information from a computer to a web site (or other remote location on a network). URL •

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A very powerful operating system used as the basis of many high-end computer applications.

Universal Power Supply or Uninterruptible Power Supply. An electrical power supply that includes a battery to provide enough power to a computer during an outage to back-up data and properly shut down.

USB •

Universal Serial Bus. An industry standard for connecting different compatible peripheral devices across multiple platforms. Devices include printers, digital cameras, scanners, game pads, joysticks, keyboards and mice, and storage devices. USB peripherals offer the use of plug-and-play convenience by eliminating the need to turn off or restart the computer when attaching a new peripheral. Users can connect USB peripherals whenever they need them. For example, a user producing a newsletter could easily swap a digital camera for a scanner-without any downtime. Small, simple, inexpensive, and easy to attach, USB supports simultaneous connection of up to 127 devices by attaching peripherals through interconnected external hubs.

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USB hubUSB hub • A multiple-socket USB connecter that allows several USBcompatible devices to be connected to a computer.

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USENET • A large unmoderated and unedited bulletin board on the Internet that offers thousands of forums, called newsgroups. These range from newsgroups exchanging information on scientific advances to celebrity fan clubs.

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user friendly • A program or device whose use is intuitive to people with a nontechnical background.

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video teleconferencing • A remote “face-to-face chat,” when two or more people using a webcam and an Internet telephone connection chat online. The webcam enables both live voice and video.

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virtual reality (VR) •

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virus •

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A technology that allows one to experience and interact with images in a simulated threedimensional environment. For example, you could design a room in a house on your computer and actually feel that you are walking around in it even though it was never built. (The Holodeck in the science-fiction TV series Star Trek: Voyager would be the ultimate virtual reality.) Current technology requires the user to wear a special helmet, viewing goggles, gloves, and other equipment that transmits and receives information from the computer. An unauthorized piece of computer code attached to a computer program or portions of a computer system that secretly copies itself from one computer to another by shared discs and over telephone and cable lines. It can destroy information stored on the computer, and in extreme cases, can destroy operability. Computers can be protected from viruses if the operator utilizes good virus prevention software and keeps the virus definitions up to date. Most viruses are not programmed to spread themselves. They have to be sent to another computer by e-mail, sharing, or applications. The worm is an exception, because it is programmed to replicate itself by sending copies to other computers listed in the e-mail address book in the computer. There are many kinds of viruses, for example:

Boot viruses place some of their code in the start-up disk sector to automatically execute when booting. Therefore, when an infected machine boots, the virus loads and runs. File viruses attached to program files (files with the extension “.exe”). When you run the infected program, the virus code executes. Macro viruses copy their macros to templates and/or other application document files. Trojan Horse is a malicious, security-breaking program that is disguised as something benign such as a screen saver or game. Worm launches an application that destroys information on your hard drive. It also sends a copy of the virus to everyone in the computer's e-mail address book.

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WAV • A sound format (pronounced “wave”) used to reproduce sounds on a computer.

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webcam • A video camera/computer setup that takes live images and sends them to a Web browser.

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Window • A portion of a computer display used in a graphical interface that enables users to select commands by pointing to illustrations or symbols with a mouse. “Windows” is also the name Microsoft adopted for its popular operating system.

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World Wide Web (“WWW” or “the Web”) • A network of servers on the Internet that use hypertext-linked databases and files. It was developed in 1989 by Tim Berners-Lee, a British computer scientist, and is now the primary platform of the Internet. The feature that distinguishes the Web from other Internet applications is its ability to display graphics in addition to text.

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word processor • A computer system or program for setting, editing, revising, correcting, storing, and printing text.

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