Computer Hardware
Overview
Purpose of this chapter is to provide a managerial overview of computer hardware by reviewing the basic types of computer systems and the major types of computer peripheral devices used for input, output, and storage.
Section I: Computer Systems: End User and Enterprise Computing
1) Analyzes the basic functions, components, and major trends in computer systems.
2) Presents an overview of microcomputer, minicomputer, mainframe, and networked computer systems.
Section II: Computer Peripherals: Input, Output, and Storage Devices
1) Discusses the major characteristics and functions of computer peripheral devices, including support of the user interface through visual and voice input/output methods.
2) Discusses the use of semiconductor memory, magnetic disks and tape, and optical disks to provide storage capabilities of computer systems.
Learning Objectives
 | Identify the components and functions of a computer system. |
| Outline the major differences and uses of microcomputers, minicomputers, mainframe, and networked computers. |
| Identify the major types and uses of computer peripherals for input, output, and storage. |
| Explain the benefits, limitations, and trends in major types of computer systems and peripheral devices. |
Computer Systems: Micros, Minis, Mainframes, and Networked Computers
The Computer System Concept:
A computer is a system of information processing components that perform input, processing, output, storage, and control functions. hus a computer system consists of input and output devices, a central processing unit (CPU), primary and secondary storage devices, and other peripheral devices.
A computer is a system of hardware devices organized according to the following system functions:
Input The input devices of a computer system include:
1. Keyboards
2. Electronic Mice
2. Touchscreens
3. LightPens
4. Optical Scanners
5. VoiceInput
They convert data into electronic machine-readable form for direct entry or though telecommunications links into a computer system.
Processing The central processing unit (CPU) is the main processing component of a computer system (in microcomputers, the CPU is the main microprocessor). One ofthe CPU's major components is the arithmetic-logic unit (ALU) that performs the arithmetic and logic functions required in computer processing.
Components of the CPU include:
1. ControlUnit
2. Arithmetic-LogicUnit
3. Primary StorageUnit
Output Convert electronic information produced by the computer system into human-intelligible form for presentation to end users.
Output devices include:
1. Video Display Units
2. Audio Response Units
3. Printers
Storage The storage function of a computer system is used to store data and program instructions needed for processing.
Storage devices include:
1. Primary Storage Unit (main memory)
2. Secondary Storage Devices (magnetic disk and tape units, optical disks)
Control The control unit interprets computer program instructions and transmits directions to the other components of the computer system.
Computer System Components:
The Central Processing Unit
The central processing unit is the most important hardware component of a computer system. It is known as the CPU, the central processor or instruction processor, and the main micro-processor in a microcomputer. The CPU can be divided into two major sub-units which include:
l. Arithmetic-logic unit
2. Control unit
The CPU also includes specialized circuitry and devices such as registers:
Arithmetic-Logic Unit: Performs the arithmetic and logic functions required in processing.
Control Unit: Interprets computer program instructions and transmits directions to the other components of the computer system.
Registers: Specialized circuits used for high-speed, temporary storage of instruction or data elements during the execution of an instruction.
Multiple Processors: Many computer systems use multiple processors for their processing functions. Instead of having one CPU with a single control unit and ALU, computers can contain several types of processing units.
The major types of multi-processor designs include:
Support Processor Specialized microprocessors that free the main CPU to do its primary job of executing program instructions. Support processors include math coprocessors, video display controllers, magnetic disk controllers.
Coupled Processor Computers can use multiple CPU's or main microprocessors to do multiprocessing, ie execution more than one instruction at the same time.
Parallel Processor Computers can use a group of instruction processors to execute many instructions at the same time - in parallel.
Massively Parallel Processor Computers can use many processors organized in clusters or networks to execution thousands of instructions at a time.
RISC Processors:
Reduced Instruction Set Computer (RISC) is a processor designed for use in advanced technical workstations. RISC processors optimize a CPU's processing speed by using a smaller number instruction set. Basically, this means that they use a smaller number of the basic machine instructions that a processor is capable of executing. By keeping the instruction set simpler and using more complex software, a RISC processor can reduce the time needed to execute program instructions. The majority of popular computer use CISC (Complex Instruction Set computer).
Computer Processing Speeds:
How fast is fast? A person taking one step each nanosecond could circle the earth about 20 times in one second. Computer speeds are categorized as:
Milliseconds Speeds measured in thousands of a second
Microseconds Speeds measured in millionths of a second
Nanoseconds Speeds measured in millionths of a second
Picoseconds Speeds measured in trillionths of a second
MIPS Speeds measured in millions of instructions per second (MIPS)
Mhz Speeds measured in millions of cycles per seccond (megahertz).
Processing speed depends on factors such as:
1. the size of circuitry paths (busses/wordsize)
2. the presence of high speed (cache) memory
3. the presence of specialized microprocessors (math coprocessor)
Primary & Secondary Storage:
Primary Storage:
The primary storage unit (main memory) holds data and instructions between processing steps and supplies them to the CU and ALU during processing. All data and programs must be placed into main memory before they can used in processed. The primary storage unit also holds data and program instructions between processing steps, and after processing is completed but before output. In modern computers, main memory consists of semiconductor memory chips. This includes RAM (random access memory) for loading programs and data before execution, and ROM (read only memory) for permanent programs that are supplied with the computer hardware.
Secondary Storage:
Secondary storage is used for long term (permanent) storage of data and programs. Secondary storage devices include magnetic disks and tape units. Before the contents of secondary storage can be processed, they must be brought into the primary (main) storage unit.
Computer Storage Capacities:
Data is processed and stored in a computer system through the presence or absence of electronic or magnetic "signals" in the computer's circuitry of in the media it uses. This is called a "two- state" or binary representation of data, since the computer and media can exhibit only two possible states or conditions.
Bit
The smallest element of data, (binary digit) which can have a value of zero or one. The capacity of memory chips is usually expressed in terms of bits.
Byte
The basic grouping of bits that the computer operates as a single unit. It typically consists of 8 bits and is used to represent one character of data in most computer coding schemes (e.g. 8 bits = 1 byte). The capacity of a computer's memory and secondary storage devices is usually expressed in terms of bytes.
Commonly used codes for representing characters in computer systems through various arrangements of bits are:
1. ASCII (American Standard Code for Information Exchange)
2. EBCDIC (Extended Binary Coded Decimal Interchange Code). Pronounced: EB SEE DICK
Kilobytes
Is a measurement of storage capacity. Abbreviated as KB or K
K = one thousand bytes (1,024 or 2'°) (i.e., 640K = 640 x 1024 = 655,360 NOT 640,000)
Megabytes
Is a measurement of storage capacity Abbreviated as MB or M
M = one million bytes (1,024 or 2[2°])
Gigabyte
Is a measurement of storage capacity. Abbreviated as GB or G
G = one billion bytes (1,024 or 2[3°])
Terabyte
Is a measurement of storage capacity. Abbreviated as TB or T
T = one trillion bytes ((1,024 or 2[4°])
Types and Trends in Computers:
Trends: Computer systems have evolved through several major stages or generations. Each generation is characterized by major changes in technology and processing power. As well, each generation has become smaller, faster, more reliable, and less costly to purchase and maintain.
Computer Generations:
Generation Time-Period Based-On
First generation 1951-1958 Vacuum Tubes
Second generation 1959-1963 Transistors
Third generation 1964-1979 Integrated Circuits
Fourth generation 1979-Present LSI/VLSI (large scale integration)
Fifth generation 1990s
Computer Categories:
Computer systems are typically classified as: (computer platforms) include: microcomputers midrange computers mainframe computers
Microcomputer Systems:
Microcomputers are the smallest but most important category of computers systems for end users. They are also referred to as personal computers (or PC's). The computing power of current microcomputers exceeds that of the mainframe computers of previous generations at a fraction of their cost. They have become powerful professional workstations for use by end users in businesses and other organizations.
Microcomputers categorized by size
1. handheld
2. notebook
3. laptop
4. portable
5. desktop
6. floor-standing
Microcomputers categorized by use
1. home
2. personal
3. professional
4. workstation
5. multiuser
Microcomputers categorized by special purpose
1. Personal Digital Assistants
2. Telecommunications Network Servers
Single-user computers
Support the work activities of a variety of end users.
Workstation computers
Support applications requiring heavy mathematical computing and graphics display demands (CAD, investment and portfolio analysis in the securities industry).
Network Servers
Support computing by several end users at multiple terminals, such as network servers that coordinate processing in the local area networks (LANs) of microcomputers and other devices. This is the fastest growing microcomputer application category. They are usually more powerful microcomputers that coordinate telecommunications and resource sharing in local area networks (LANs) of interconnected microcomputers and other computer system devices.
Midrange Computer Systems
Midrange computers (minicomputers) are general purpose computers that are larger and more powerful than most microcomputers but are smaller and less powerful than most large mainframes.
Cost less to buy and maintain than mainframe computers.
Can function in ordinary operating environments (do not need air conditioning or electrical wiring).
Smaller models of minicomputers do not need a staff of specialists to operate them.
Applications:
Used for a large number of business and scientific applications (scientific research, instru-mentation systems, engineering analysis, and industrial process monitoring and control)
Serve as industrial process-control and manufacturing plant computers, and they play a major role in computer-aided manufacturing (CAM), and computer-aided design (CAD) applications.
Used as front-end computers to help mainframe computers control data communications networks and large numbers of data entry terminals.
Are popular as powerful network servers in department, offices, and work sites.
Mainframe Computer Systems
Are large, powerful computers that are physically larger and more powerful than micros and minis.
Usually have one or more central processors with faster instruction processing speeds (MIPS)
Have large primary storage capacities.
Can support more input/output and secondary storage devices
Can support hundreds of users concurrently
Cost more to buy and maintain than mini computers
Most mainframe computers need to operate in special environments (air conditioning and special wiring)
Professionals are required to operate them
Applications:
Handle the information processing needs of government agencies and business organizations with many employees and customers
Handle enormous and complex computational problems
Act as host computers for distributed processing networks that include smaller computers
Used in National and International computing networks.
Supercomputer Systems:
Are a special category of extremely powerful mainframe computer systems specifically designed for high-speed numeric computation.
Applications
Government agencies
Military defense systems
National weather forecasting agencies
Large time-sharing networks
Major corporations.
Networked Computer Systems:
Solitary computer systems are becoming a rarity in corporate computing. Increasingly, computers are being networked or interconnected by telecommunication links with other computer systems. This distribution of computer power throughout an organization is called distributed processing. Distributed processing takes the form of client/server approach, with networks of end user microcomputers (clients) and network servers tied together, sometimes with minicomputers or mainframes acting as super-servers.
Benefits:
Networked computer systems allow end users to communicate electronically an share the use of hardware, software, and data resources.
Networks of small computers have become a major alternative to the use of larger computer systems, as many organizations downsize their computing platforms. For example, a local area network (LAN) of microcomputers can replace the use of groups of end user terminals connected to a minicomputer or mainframe.
Telecommunications (data communications) is the use of networks of interconnected computers and peripheral devices to process and exchange data and information. Telecommunications networks require a variety of telecommunications media, hardware, and software to accomplish and control communications among computers and peripheral devices.
Networked ComputerApplicntions:
Networked microcomputer systems are being used in place of minicomputers and mainframes. Are easy to install, use, and maintain, and provide a more efficient, flexible, lower-cost alternative to large computer systems for many applications. Used to share computer power, software, and databases require in time-sharing and resource-sharing applications. Networked computers also support work group computing (communicate electronically and share data on joint projects). Used in transaction processing applications.
Computer Peripherals: Input, Output & Storage Devices
Peripherals - is the generic name for all input/output equipment and secondary storage devices that depend on direct connections or telecommunications links to the central processing unit of a computer system. Thus, all peripherals are online devices, that is, separate from, but can be electronically connected to and controlled by, a CPU. This is the opposite of offline devices, which are separate from and not under the control of the CPU.
Input/Output Hardware Trends:
There are many hardware devices for input and output at the user interface between computer systems and end users.
Trend:
Toward the increased use of direct input/output devices to provide a more natural user interface. Direct input/output devices drastically reduce the need for paper source documents and their conversion to machine-readable media.
Input:
More and more data and instructions are entered into a computer system directly through input devices such as keyboards, electronic mice, pens, touch screens, optical scanning wands, etc. The most common user interface method for input is the keyboard.
Output:
Direct output of information through video displays of text and graphics and voice response devices is increasingly becoming the dominant form of output for end users. The most common user interface method for output is the video display screen.
Computer Terminal Trends:
Computer terminals of various types are widely used for input and output.
Computer Terminals: A device that allows remote input to and output from a computer.
Visual Display Terminal (VDT): A terminal that uses a keyboard for input and a TV like screen for visual output, or Cathode Ray Tube (CRT) terminal.
Dumb Terminals Have no processing capabilities. They can only perforrn input and output. There is now a trend away from them towards intelligent terminals.
Intelligent Terminals Have their own microprocessors and memory circuits.
Transaction Terminals Capture data from end users during a transaction and transmit it over telecommunications networks to a computer system for processing. Examples: ATM, retail point-of-sale (POS) terminals.
Pointing Devices:
Pointing devices allow end users to issue commands or make choices by moving a cursor on the display screen. Pointing devices allow the user to easily choose from menu selections and icon displays using point-and-click or point-and-drag methods.
Icons are small figures that look like familiar devices. e.g. file folder, wastebasket, calculator, calendar etc. Using icons helps simplify computer use since they are easier to use with point devices than menus and other text-based displays.
Examples of pointing devices are:
1. electronic mouse
2. trackball
3. point stick
4. touch-sensitive screens
Electronic Mouse:
A device used to move the cursor on the screen, as well as to issue commands and make icon and menu selections.
Trackball:
A device used to move the cursor on the display screen.
Point Stick:
A small button like device, sometimes likened to the eraser head of a pencil. The cursor moves in the direction of the pressure you place on the track-point.
Touch-Sensitive Screens:
A device that accepts data input by the placement of a finger on or close to the CRT screen.
Pen-Based Computing:
End users can write or draw directly on a video screen or on other surfaces using a variety of pen like devices. Light pen and graphics pad technologies are being used in a new generation of pen based personal computers and personal digital assistants that recognize handwriting.
Light Pen A photo electronic device that allows data to be entered are altered on the face of a video display terminal.
A device that allows an end user to draw or write on a pressure sensitive tablet and have their handwriting or graphics digitized by the computer and accepted as input.Graphics Tablet
Pointing Devices:
Pointing devices allow end users to issue commands or make choices by moving a cursor on the display screen. Pointing devices allow the user to easily choose from menu selections and icon displays using point-and-click or point-and-drag methods.
Icons are small figures that look like familiar devices. e.g. file folder, wastebasket, calculator, calender etc. Using icons helps simplify computer use since they are easier to use with point devices than menus and other text-based displays.
Examples of pointing devices are:
- electronic mouse;
- trackball;
- point stick;
- touch-sensitive screens
Electronic Mouse:
A device used to move the cursor on the screen, as well as to issue commands and make icon and menu selections.
Trackball: A device used to move the cursor on the display screen.
Point Stick: A small button like device, sometimes likened to the eraser head of a pencil. The cursor moves in the direction of the pressure you place on the trackpoint.
Touch-Sensitive Screens: A device that accepts data input by the placement of a finger on or close to the CRT screen.
Pen-Based Computing:
End users can write or draw directly on a video screen or on other surfaces using a variety of pen like devices. Light pen and graphics pad technologies are being used in a new generation of pen based personal computers and personal digital assistants that recognize handwriting.
Light Pen A photo electronic device that allows data to be entered are altered on the face of a video display terminal.
Graphics Tablet A device that allows an end user to draw or write on a pressure sensitive tablet and have their handwriting or graphics digitized by the computer and accepted as input.
Video Input/Output:
Video & Multimedia Input: Input can take the form of a video images captured with a TV receiver, camcorder, or VCR that can be digitized and compressed for storage on magnetic or optical disk.
Video Output: Video displays are the most common type of computer output. Most video displays use a cathode ray tube (CRT) technology.
Liquid crystal displays (LCD's) are commonly used for portable microcomputers and terminals. They use less electricity that the CRT and provide a thin, flat display.
Plasma displays use electrically charged particles of gas (plasma) trapped between glass plates. They are significantly more expensive than CRT and LCD units. However, they use less power and provide for faster display speed and better quality displays.
Printed Output:
After video displays, printed output is the most common form of visual output for the user interface. Most computers use printers to produce permanent (hard copy) output in human readable form.
Plotters: Devices that draw graphics displays on paper, they also produce printed paper output.
Impact Printers: Form characters and other images on paper through the impact of a printing mechanism that presses a printing element and an inked ribbon or roller against the face of a sheet of paper (e.g., dot matrix printers, high-speed line printers).
Non-Impact Printers Do not utilize a printing mechanism (e.g., laser printers and ink jet printers).
Voice Recognition and Response:
Voice recognition and voice response (in their infancy) promise to be the easiest method of providing user interface for data entry and conversational computing, since speech is the easiest, most natural means of human communication.
Voice Recognition: These systems analyze and classify speech or vocal tract patterns and convert them into digital codes for entry into a computer system.
Used in work situations where operators need to perform data entry without using their hands to key in data or instructions, or where it would be faster and more accurate input.
Voice Response: These systems are more developed that voice recognition. Devices range from mainframe audio-response units to voice-messaging minicomputers to speech synthesizer microprocessors.
Used to guide operators through the steps of a task, and also used to allow computers to respond to verbal and touch-tone input over the telephone.
Optical and Magnetic Recognition:
Optical Scanning: An input device (scanner) that scans characters or images and generates their digital representations. They include optical character recognition (OCR) equipment that can read special-purpose characters and codes, and wands that are used to read data on merchandise tags and other media.
Magnetic Data Entry:
The machine recognition of characters printed with magnetic ink. Primarily used for check processing magnetic ink character recognition (MICR by the banking industry. Another form of magnetic data entry is the magnetic stripe technology used to machine read credit cards.
Storage Trends and Trade-Off:
Data and information need to be stored after input, during processing, and before output.
Storage Trends: Away from paper documents stored in filing cabinets to computer- based information storage.
Storage Trade-Offs: As access speed increases, storage capacity decreases, and the cost per bit increases.
Semiconductor memories are used mainly for primary storage. Trade offs that a lose or interruption of electrical power results in lost data.
Magnetic disk, tape, and optical disk devices are used as secondary storage to enlarge the storage capacity of computer systems. Advantage is that the data is more secure than semiconductor memory as it is more permanent.
Direct and Sequential Access:
Direct Access:
A method of storage where each storage position has a unique address and can be individually accessed in approximately the same period of time without having to search through other storage positions. Primary storage media such as semiconductor memory chips are called direct access or random access memory (RAM).
Sequential Access:
A sequential method of storing and retrieving data from a file. This type of storage media do not have unique storage addresses that can be directly addressed. Instead, data must be stored and retrieved using a sequential or serial process. Data are recorded one after another in a predetermined sequence on a storage medium. Locating an individual item of data requires searching much of the recorded data on the tape until the desired item is located.
Semiconductor Memory:
The primary storage (main memory) on most modern computers consists of microelectronic semiconductor memory circuits. Memory chips with capacities of 256K bits, 1 megabit, 4 megabits, 16 megabits, and 32 megabits are not being used in many computers.
Advantages of semiconductor memory are:
1. Small size
2. Fast speed
3. Shock and temperature resistance
4. Reasonably low cost due to mass production.
Disadvantage of semiconductor memory are:
1. Volatility (IJninterrupted electric power must be supplied or the contents of memory will be lost (except with read only memory, which is permanent).
Two basic types of semiconductor memory:
Random Access Memory (RAM):
These memory chips are the most widely used primary storage medium. Each memory position can be both read and written, so it is also called read/write memory. This is a volatile memory.
Read Only Memory (ROM):
Nonvolatile random access memory chips are used for permanent storage. ROM can be read but not erased or overwritten. Instructions and programs in primary storage can be permanently "burned in" to the storage cells during manufacturing. This is permanent software is also called firmware. Variations include PROM (programmable read only memory) and EPROM (erasable programmable read only memory) which can be permanently or temporarily programmed after manufacture.
Semiconductor Secondary Storage:
Semiconductor memory chips are used as primary and secondary storage media for both large and small computers. These are additional circuit boards that can be added to a computer system to increase its memory capacity. These provide additional primary storage, but they can also be used for secondary storage. A computer's operating system program can be instructed to treat part of RAM as if another disk drive has been added to the system. This provides a very high speed semiconductor secondary storage capability, sometimes called a RAM disk.
Magnetic Disk Storage:
These are the most common form of secondary storage for modern computer systems.
Advantages of magnetic disk storage:
1. Fast access
2. High storage capacities
3. Reasonable cost.
The two basic types of magnetic disk media are:
1. Conventional (hard) metal disks
2. Flexible (floppy) diskettes.
Magnetic Disks
Thin metal or plastic disks that are coated on both sides with an iron oxide recording material. They record data on circular tracks in the form of tiny magnetized sports representing binary digits. All tracks with equal radius on a disk make up a cylinder. A disk surface is divided into pie-shared sectors.
Types of Magnetic Disks
There are several types of magnetic disk arrangements, including removable disk packs and cartridges as well as fixed disk units. The removable disk devices are popular because they can be used interchangeable in magnetic disk units and stored offline for convenience and security when not in use.
Floppy Disks:
A small plastic disk coated with iron oxide that resembles a small phonograph record enclosed in a protective envelope. It is a widely used form of magnetic disk media that provides a direct access storage capability for microcomputer systems.
Hard Disk Units:
A combination of magnetic disks coated with iron oxide, and sealed into a module. These non-removable devices allow higher speeds, greater data-recording densities, and closer tolerances within a sealed, more stable environment.
RAID:
Large-capacity mainframe disk drives are being challenged by disk arrays of interconnected microcomputer hard disk drives to provide many gigabytes of online storage. RAID (Redundant arrays of inexpensive disks).
Advantages:
1. Provide large capacities with high access speeds since data is accessed in parallel over multiple paths from many disks.
2. Provide fault tolerant capability, since their redundant design offers multiple copies of data on several disks. If one disk fails, data can be recovered from backup copies automatically stored on other disks.
Magnetic Tape Storage:
Magnetic Tape:
A plastic tape with a magnetic surface on which data can be stored by selective magnetization of portions of the surface.
Optical Disk Storage:
Technology based on using a laser to read tiny spots on a plastic disk. The disks are currently capable of storing billions of characters of information.
CD-ROM
A common type of optical disk used on microcomputers. There are used for read only storage. Storage is over 600 megabytes per disk. Data are recorded as microscopic pits in a spiral track, and are read using a laser device.
WORM
Write Once, Read Many. The data is stored once on the disk, however, it can be read an infinite number of times.
CD-R
"Compact disk recordable" disks (same as WORM).
Disadvantage of CD-ROM, WORM, and CD-R:
1. Recorded data cannot be erased. However, erasable optical disk systems are now available.
Major use of optical disks in mainframe and midrange systems is:
1. Image processing, where long-term archival storage of historical files of document images must be maintained.
Major use of CD-ROM disks is:
1. Provide companies with fast access to reference materials in a convenient, compact form.
2. Interactive multimedia applications in business, education, and entertainment. Multimedia is the use of a variety of media, including text and graphics displays, voice, music, and other audio, photographs, animation, and video segments.
Key Terms and Concepts
Arithmetic-Logic Unit
The unit of a computing system containing the circuits that perform arithmetic and logical operations.
Binary Representation
Pertaining to the presence or absence of electronic or magnetic "signals" in the computer’s circuitry or in the media it uses. There are only two possible states or conditions, presence or absence.
Cathode Ray Tube (CRT)
An electronic vacuum tube that displays the output of a computer system.
Central Processing Unit (CPU)
The unit of a computer system that includes the circuits that control the interpretation and execution of instructions. In many computer systems, the CPU includes the arithmetic logic unit, the control unit, and primary storage unit.
Client/Server
A computing environment where end user workstations (clients) are connected to micro or mini LAN servers and possibly to mainframe super-servers.
Computer System
Computer hardware as a system of input, processing, output, storage, and control components. Thus a computer system consists of input and output devices, primary and secondary storage devices, the central processing unit, the control unit within the CPU, and other peripheral devices.
Computer Terminals
Any input/output device connected by telecommunications links to a computer.
Control Unit
A sub-unit of the central processing unit that controls and directs the operations of the computer system. The control unit retrieves computer instructions in proper sequence, interprets each instruction, and then directs the other parts of the computer system in their implementation.
Direct Access
A method of storage where each storage position has a unique address and can be individually accessed in approximately the same period of time without having to search through other storage positions.
Direct Input/Output Devices
Devices such as terminals that allow data to be input into a computer system or output from the computer system without the use of machine-readable media.
Distributed Processing
A form of decentralization of information processing made possible by a network of computers dispensed throughout an organization. Processing of user applications is accomplished by several computers interconnected by a telecommunications network rather than relying on one large centralized computer facility or on the decentralized operation of several independent computers.
Downsizing
Downsizing computer platforms results from using networks of microcomputers to replace minicomputers and mainframes.
Generations of Computing
Reflect stages in the development of electronic computers, characterized by major changes in technology or performance.
Graphics Tablet
A device that allows an end user to draw or write on a pressure sensitive tablet and have their handwriting or graphics digitized by the computer and accepted as input.
Icon
A small figure on a video display that looks like a familiar office or other device such as a file folder (for storing a file), a wastebasket (for deleting a file), or a calculator (for switching to a calculator mode).
Light Pen
A photo electronic device that allows data to be entered are altered on the face of a video display terminal.
Liquid Crystal Displays
(LCD) Electronic visual displays that forrn characters by applying an electrical charge to selected silicon crystals.
Local Area Network
A communications network that typically connects computers, terminals, and other computerized devices within a limited physical area such as an office, building, manufacturing plant, or other worksite.
Magnetic Disk Storage
Data storage technology that uses magnetized sports on metal or plastic disks.
Floppy Disk
A small plastic disk coated with iron oxide that resembles a small phonograph record enclosed in a protective envelope. It is a widely used form of magnetic disk media that provides a direct access storage capability for microcomputer systems.
Hard Disk
Secondary storage medium; generally non-removable disks made out of metal and covered with a magnetic recording surface. It holds data in the form of magnetized sports.
Magnetic Ink Character Recognition (MICR)
The machine recognition of characters printed with magnetic ink. Primarily used for check processing by the banking industry.
Magnetic Tape
A plastic tape with a magnetic surface on which data can be stored by selective magnetization of portions of the surface.
Mainframe Computer
A larger-size computer system, typically with a separate central processing unit, as distinguished from microcomputer and minicomputer systems.
Microcomputer
A very small computer, ranging in size from a "Computer on a chip" to a small typewriter-size unit.
Microprocessor
A semi-conductor chip with circuitry for processing data.
Midrange Computer
Are larger and more powerful than most microcomputers but are smaller and less powerful than most large mainframe computer systems.
Minicomputer
A small electronic general-purpose computer.
Multimedia
Refers to technology that presents information in more than one medium, including text, graphics, animation, video, sound effects, music, and voice.
Multiple Processors
Refers to computers with more than one major processing element.
Network Server
Are computers that are more powerful than microcomputers. They are used to coordinate telecommunications and resource sharing in local area networks of interconnected microcomputers and other computer system devices.
Networked Computer Systems
Multiple computer systems connected via telecommunications networks.
Offline
Pertaining to equipment or devices not under control of the central processing unit.
Online
Pertaining to equipment or devices under control of the central processing unit.
Optical Character Recognition (OCR)
The machine identification of printed characters through the use of light-sensitive devices.
Optical Disk Storage
Technology based on using a laser to read tiny spots on a plastic disk. The disks are currently capable of storing billions of characters of information.
CD-ROM
An optical disk technology for microcomputers featuring compact disks with a storage capacity of over 500 megabytes.
Erasable Disk
Optical disk that allows users to erase data so that the disk can be used over and over again.
WORM Disk
Optical disk that allows users to write once, read many times.
Optical Scanning
Using a device (scanner) that scans characters or images and generates their digital representations.
Pen-Based Computing
Tablet-style microcomputers that recognize hand-writing and hand drawing done by a pen-shaped device on their pressure sensitive display screens.
Peripheral Devices
In a computer system, any unit of equipment, distinct from the central processing unit, that provides the system with input, output, or storage capabilities.
Plasma Displays
Output devices that generate a visual display with electronically charged particles of gas trapped between glass plates.
Plotters
A hard-copy output device that produces drawings and graphical displays on paper or other materials.
Pointing Devices
Devices which allow end users to issue commands or make choices by moving a cursor on the display screen.
Electronic Mouse
A small device that is electronically connected to a computer and is moved by hand on a flat surface in order to move the cursor on a video screen in the same direction. Buttons on the mouse allow users to issue commands and make responses or selections.
Point Stick
A small button-like device sometimes likened to the eraser head of a pencil. The cursor moves in the direction of the pressure you place on the trackpoint.
Trackball
A roller device set in a case used to move the cursor on a computer's display screen.
Primary Storage Unit
The main (or internal) memory of a computer. Usually in the form of semiconductor storage.
Printers
A device that produces hard copy output such as paper documents or reports.
Processing Speeds
Speed at which data can be manipulated to process it into information .
Secondary Storage Device
External or auxiliary storage device that supplements the primary storage of a computer.
Semiconductor Memory
Microelectronic storage circuitry etched on tiny chips of silicon or other semi-conducting material.
RAM
Also known as main memory or primary storage; type of memory that temporarily holds data and instructions needed shortly by the CPU. RAM is a volatile type of storage.
ROM
Also known as firmware; a memory chip that permanently ores instructions and data that are programmed during the chip's manufacture. Three variations on the ROM chip are PROM, EPROM, and EEPROM. ROM is a nonvolatile form of storage.
Sequential Access
A sequential method of storing and retrieving data from a file.
Storage Capacity Elements
Units used for storage capacity and data: bits, bytes, kilobytes (KB), megabytes (MB), gigabytes (GB), terabytes (TB).
Bit
A contraction of "binary digit". It can have the value of either 0 or 1.
Byte
A sequence of adjacent binary digits operated on as a unit and usually shorter than a computer word. In many computer systems, a byte is a grouping of eight bits that can represent one alphabetic or special character or can be "packed" with two decimal digits.
Kilobyte (K or KB)
When referring to computer storage capacity it is equivalent to 2 to the 10th power, or 1,014 in decimal notation.
Megabyte (MB)
One million bytes. More accurately, 2 to the 20th power, 1,048,576 in decimal notation.
Gigabyte (GB)
One billion bytes. More accurately, 2 to the 30th power, or 1,073,741,824 in decimal notation.
Terabyte (TB)
One trillion bytes. More accurately, 2 to the 40th power, or 1,009,511,627,776 in decimal notation.
Storage Media Trade-Offs
The trade-offs in cost, speed, and capacity of various storage media.
Supercomputer
A special category of large computer systems that are the most powerful available. They are designed to solve massive computational problems.
Time Elements
Units used for measuring processing speeds: milliseconds, microseconds, nanoseconds, picoseconds.
Millisecond
A thousandth of a second.
Microsecond
A millionth of a second.
Nanosecond
One billionth of a second.
Picosecond
One trillionth of a second.
Touch-Sensitive Screen
An input device that accepts data input by the placement of a finger on or close to the CRT screen.
Trends in Computers
Smaller, faster, and cheaper.
Vidoe Input/Output
Video input can serve as input as well as output. Video displays are the most common type of computer output.
Voice Recognition
Direct conversion of spoken data into electronic form suitable for entry into a computer system. Also called voice data entry.
Voice Response
Output that emerges as spoken words rather than as a visual display.
Volatility
Memory (such as electronic semiconductor memory) that loses its contents when electrical power is interrupted.
Wand
A handheld optical character recognition device used for data entry by many transaction terminals.
Workstation
A computer terminal or micro or mini computer system designed to support the work of one person. Also, a high-powered computer to support the work of professionals in engineering, science, and other areas that require executive computing power and graphics capabilities.