Chapter 4
Information Systems Hardware
4.1 Organization of Computer Systems
Almost all computer systems have a similar, rather simple, structure consisting of a processor, main memory, and peripheral devices such as secondary storage, and input and output devices.
What is the Structure of a Computer System? [Figure 4.1][Slide 4-1]
A computer system is a set of devices that can accept and store programs and data, execute programs by applying their instructions to the data, and reporting the results.
Figure 4.1 explains the general organization of computer system hardware. The principal components of a computer system are the processor, main memory, input and output devices, and secondary storage. Stress to students that the same organization is used to build a microcomputer for a desktop or for a mainframe.
The Processor (CPU)
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 microprocessor in a microcomputer. 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 the media it uses. This is called a Atwo-state or binary representation of data, since the computer and media can exhibit only two possible states or conditions (1s and 0s).
The CPU can be divided into two major subunits which include the arithmetic-logic unit (ALU) which performs the arithmetic and logic functions required in processing and the control unit which interprets computer program instructions and transmits directions to the other components of the computer system.
Main Memory [Figure 4.2][Slide 4-4]
The main memory is a fast electronic component of the computer system that serves to store programs to be executed by the CPU and the data these programs require. A main memory consists of a large number of locations, identified by their addresses, as shown in Figure 4.2.
A bit is 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, whereas a byte is 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. A word is the largest number of consecutive bytes that can be accessed at one time in the main memory.
Commonly used codes for representing characters in computer systems through various arrangements of bits are:
1. ACSII (American Standard Code for Information Exchange)
2. EBCDIC (Extended Binary Coded Decimal Interchange Code) - pronounced: EB SEE DICK
Multimedia computing integrates various media, such as text, graphics, sound, and video, is becoming more popular and therefore, images are often stored as well. A memory representation of an image is the equivalent of a grid of dots called pixels (picture elements).
The primary storage (main memory) on most modern computers consists of microelectronic semiconductor memory circuits, referred to as RAM (random access memory). Memory chips with capacities of 256K bits, 1 megabit, 4 megabits, 16 megabits, and 32 megabits are now 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 (uninterrupted 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:
1. Random Access Memory (RAM):
- these memory chips are the most widely used primary storage mediums. Each memory position can be both read and written, so it is also called read/write memory. This is a volatile memory.
2. 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.
Peripherals
Secondary storage devices (such as disks and tape drives), along with input and output devices are called peripherals, input and output devices transfer programs and data between the outside world and the main memory.
4.2 Computer Categories: Microcomputers, Mainframes, and Supercomputers
Computer system hardware is now available in a spectacular variety of capabilities and costs. The relative cost of hardware as compared to software has declined no less impressively. The challenge consists in using information technology to increase operational efficiency and managerial effectiveness, and, ultimately, to deploy it to seek competitive advantage.
What are the Categories of Computers:
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. The principal characteristic of a computer generation is the fundamental technology employed to build computer circuits. Very large-scale integration (VLSI) made it feasible to place millions of semiconductor devices on a single silicon chip. This translates into the high speeds of processor chips and the high capacities of memory chips.
Computer Generations: [Figure 4.3]
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 systems are typically classified in four categories: [Figure 4.3]
1. Microcomputers
2. Minicomputers (midrange) computers
3. Mainframe computers
4. Supercomputers.
Microcomputers [Figure 4.4][Slide 4-5]
Microcomputers are the smallest but most important categories 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 and technical workstations being used by end users in businesses and other organizations such as industrial design where high-resolution graphic processing is required.
Some microcomputers and almost all technical workstations are now built around microprocessors called reduced instruction set computers (RISC). 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, RISC processors can reduce the time needed to execute program instructions. The majority of popular computers use CISC (Complex Instruction Set Computer).
Microcomputers Microcomputers Microcomputers
categorized by size categorized by use categorized by special purpose
1. Handheld 1. Home 1. Personal Digital Assistants
2. Notebook 2. Personal 2. Network Computers
3. Laptop 3. Professional
4. Portable 4. Workstation
5. Desktop 5. Multiuser
6. Floor-standing
Minicomputers (midrange)
Minicomputers entered the business scene from scientific and engineering applications.
1. Are general purpose computers that are larger and more powerful than most microcomputers but are smaller and less powerful than most large mainframes.
2. Are often used as dedicated processors for computer-assisted design (CAD) or on-line transaction processing (OLTP), where real-time demands of fast response have to be met.
3. Often employed as corporate computers in mid-size organizations or as departmental computers in larger firms, where they communicate with personal computers on the one hand and with corporate mainframes on the other.
4. Cost less to buy and maintain than mainframe computers.
5. Can function in ordinary operating environments (do not need air conditioning or electrical wiring).
6. Smaller models of minicomputers do not need a staff of specialists to operate them.
Applications:
1. Used for a large number of business and scientific applications (scientific research, instrumentation systems, engineering analysis, and industrial process monitoring and control)
2. 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.
3. Used as front-end computers to help mainframe computers control data communications networks and large numbers of data entry terminals.
4. Are popular as powerful network servers in department, offices, and work sites.
Mainframes
The traditional sharp distinction between minicomputers and mainframes is becoming cloudy. However, mainframes are still considered the largest computers in general use.
1. Are large, powerful computers that are physically larger and more powerful than micros and minis.
2. Usually have one or more central processors with faster instruction processing speeds (MIPS).
3. Have large primary storage capacities.
4. Can support more input/output and secondary storage devices.
5. Can support hundreds of users concurrently.
6. Cost more to buy and maintain than mini computers.
7. Most mainframe computers need to operate in special environments (air conditioning and special wiring)
8. Professionals are required to operate them.
Applications:
1. Handle the information processing needs of government agencies and business organizations with many employees and customers
2. Handle enormous and complex computational problems.
3. Act as host computers for distributed processing networks that include smaller computers. Used in National and International computing networks.
Supercomputers
Are a special category of extremely powerful mainframe computer systems specifically designed for high-speed numeric computations. They are capable of carrying out billions of arithmetic operations per second. Supercomputers, exploit several design approaches, all based on parallel processing at some level of computer design. In parallel processing, impressive speeds are achieved by performing a large number of operations simultaneously.
Traditional supercomputing is being successfully challenged by massively parallel computing - systems that last together hundreds, or even thousands, of microprocessors.
Applications:
1. Government agencies
2. Military defence systems
3. National weather forecasting agencies
4. Large timesharing networks
5. Major corporations.
4.3 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 units. Magnetic technologies (disks and tapes) are now being challenged by optical disks for use as secondary storage devices.
Memory Hierarchy
A demand for computer memory has grown steadily throughout the history of computers. A variety of memory technologies offer a tradeoff between high speed on the one hand and low costs and high capacity on the other. Computer memories are therefore organized into a hierarchy. Explanation of memory hierarchy:
Semiconductor Memories: [Figure 4.8][Slide 4-6]
1. At the top of this hierarchy, the fastest memory units are actually registers included in the CPU, where data are brought in to be manipulated by the ALU which performs the arithmetic and logic functions required in processing. The registers in the CPU are specialized circuits which are used for high-speed, temporary storage of instruction or data elements during the execution of an instruction.
2. Cache memory is a high-speed temporary storage area in the CPU for storing parts of a program or data during processing.
3. Main memory is used to store the programs currently being processed, as well as the data they currently need or produce.
4. Semiconductor memory is volatile - their contents are lost when power is turned off.
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 (uninterrupted electric power must be supplied or the contents of memory will be lost (except with read only memory, which is permanent)).
Secondary Storage (lower stages of the memory hierarchy)
Magnetic disk or erasable optical disk & Magnetic tape or nonerasable optical disk
1. These devices offer nonvolatile, permanent means of storing large volumes of programs and data.
2. To be used by the processor, these programs and data items must first be transferred to the main memory.
3. These devices offer nonvolatile, permanent means of storing large volumes of programs and data.
4. The principal device for on-line storage today is the magnetic disk. The medium used for archival storage is magnetic tape. Optical disks suffer from the disadvantage of slower speeds, but their higher storage capacities make them a competitor of the magnetic media as a means for secondary storage.
Computer storage elements: [Table 4.3]
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 Is 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.
Kilobytes Is a measurement of storage capacity. Abbreviated as KB or K = one thousand bytes (1,024 or 210)
E.g., 640K = 640 x 1024 = 655,360 NOT 640,000
Megabytes Is a measurement of storage capacity. Abbreviated as MB or M = one million bytes (1,024 or 220)
Gigabyte Is a measurement of storage capacity. Abbreviated as GB or G = one billion bytes (1,024 or 230)
Terabyte Is a measurement of storage capacity. Abbreviated as TB or T = one trillion bytes ((1,024 or 240)
Magnetic Disks
Magnetic disks are secondary storage devices that afford the capability of both direct (random) and sequential access to records. Sequential access means that all records must be accessed in the sequence in which they are stored until the desired record is reached. Direct access to a record means that the record can be accessed by its disk address, without the need to access any intermediate records.
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 are 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 radiuses on a disk make up a cylinder. A disk surface is divided into pie-shared sectors.
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 nonremovable 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
Magnetic Tape is a plastic tape with a magnetic surface on which data can be stored by selective magnetization of portions of the surface. Magnetic tape has an obvious limitation - it permits only sequential access. However, it is the least expensive of the commonly used storage media and is widely used to back up magnetic disks, although it has also been employed for on-line secondary storage in the batch applications of many legacy systems.
Optical Disks
Optical technologies, which offer far higher storage densities and thus far higher capacities than magnetic devices, are revolutionizing secondary storage. Most exciting is the expansion of computer capabilities in the direction of multimedia.
Optical disks offer direct access to information. The technology is 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. The main disadvantage is slower access as compared to magnetic disks.
CD-ROM
A most common type of optical disk used on microcomputers. There are used for read only storage. Storage is more than 600 megabytes per disk. This is equivalent of more than 400 (1.44 megabyte floppy) disks or 300,000 double-spaced pages of text. 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. They are used mainly to store archival information.
Disadvantage of CD-ROM, WORM:
1. Recorded data cannot be erased.
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.
Erasable Optical Disks
Erasable optical disks are full-fledged competitors of magnetic disks. Their access time is slower than magnetic disks. However, their capacities are high for a microcomputer configuration. They offer unlimited capacity because the cartridge is removable, and they also can be securely stored away from the compute
4.4 Input Devices
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.
Keyboards
The keyboard is the principal input device in virtually all microcomputers. A variety of special-purpose keyboards are used for data input in various applications, such as securities trading or fast-food outlets.
The general trend is away from keyboarding and toward direct capture of data at the source with devices for source data automation: the use of input technologies that capture data in a computer-readable form as the data are created.
Pointing Devices:
Pointing devices allow end users to issue commands or make choices by moving a cursor on the display screen. Pointing devices such as the mouse enables users 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 folders, wastebaskets, calculators, calendars etc. Using icons helps simplify computer use since they are easier to use with point devices than menus and other text-based displays.
Devices for Direct Date Entry [Figures 4.11 & 4.12]
Image Scanners: Input device that digitizes and enters into computer memory images of figures, photographs, or signed documents.
OCR Scanner: Optical Character Recognition Scanners consist of a combination of hardware and software that can recognize printed or typed text and various codes and enter the corresponding characters into computer memory.
Bar-Code Scanner Input device that reads bar code.
Smart Card Plastic cards that carries data on a built-in semiconductor chip, or on a laser-optic or magnetic strip.
Voice Data Entry Relying on the devices that can accept spoken input.
4.5 Output Devices
The principal output devices are video displays for soft-copy and printers for hard-copy output.
Video Displays
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 display - 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.
An X-terminal can be utilized by a user from a workstation other than their own. An X terminal has a limited processing capability, is used to access services provided by other computers to which it is connected. Such a terminal includes a keyboard and a mouse, but no disk drive, and gives its user a window-type interface.
Printers and Other Hard-Copy Output Devices
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.
Impact Printers
Are printers that 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
Are printers which do not utilize a printing mechanism (e.g., laser printers and ink jet printers).
Plotters
Are output devices that draw graphics displays on paper. Also, produce printed paper output.
4.6 Enriching Business Systems with Multimedia [Figure 4.15][Slide4-7]
As computing power and storage capacities are matched by the growing telecommunications capabilities, multimedia computing increasingly enters business life. Multimedia computing integrates various media, such as text, data, graphics, sound, still images, and motion video, and enables the user to interact with such a system.
The most advanced applications of multimedia computing are the virtual reality (VR) systems that immerse users in three-dimensional artificial worlds, creating an illusion of an alternative reality.
Multimedia computing is increasingly enabling innovative systems in various business domains such as:
1. Marketing
2. Engineering and manufacturing
3. Human resource management
4. Training