computer system

Comprehensive Definition of a Computer

Functional Definition: A computer is an electronic device that accepts data and instructions, translating that data into a functional, meaningful form with high levels of speed and accuracy.
Operational Cycle: It acts as a machine that: - Accepts data from an input device. - Stores data temporarily within internal memory. - Performs arithmetic and logical operations. - Relays processed information through an output device.
Programmatic Control: It is a device operating under the control of stored programs, automatically accepting, storing, and processing data to yield specific results.
Processed Information Forms: - Data: Examples include invoices, sales ledgers, purchase ledgers, payroll, and stock controls. - Text: Frequently utilized in offices via microcomputers. - Graphics: Includes business graphs and symbols. - Images: Visual pictures. - Voice: Communication data, such as telephone audio.
Processing Activities: Includes the actions of creating, manipulating, storing, accessing, and transmitting information.

Salient Characteristics of a Computer

Operating Speed: Computers function at significantly higher speeds than manual data processing tools. This speed is measured in Hertz ( $Hz$ ).
High Accuracy: Computers are consistently accurate; the specific degree of accuracy depends on the machine's design. Errors are typically attributed to human entry mistakes or technical weaknesses rather than the machine's logic.
Diligence and Reliability: Unlike humans, computers do not suffer from fatigue, lack of concentration, or lack of cooperation, enabling them to work for extended periods.
Versatility: A computer is capable of performing any task provided it has been programmed for that specific action.
Data Manipulation: They can process diverse data types, including numbers, text, and visual pictures.
Networking Capabilities: Through networking, computers transfer information across different physical locations.
Compact Storage: Data is stored efficiently to save physical and digital storage space.
Intelligent Quotient (IQ): A computer's IQ is zero. It cannot think independently and only performs tasks as instructed by humans; its superiority lies strictly in speed and accuracy.

Core Computing Terminology

Computer Program: A set of instructions controlling the computer's data processing. These follow an orderly set of actions defined by individuals known as programmers.
Data: Refers to raw facts that have not been processed. Data is not meaningful for decision-making until it is processed. Examples include hours worked, names, and rates of pay.
Information: Data that has undergone processing to become useful to recipients for decision-making. Examples include net pay and total statutory deductions.

Advantages of Computer Systems Over Manual Systems

Speed: Measured by the number of instructions executed per second.
Accuracy: Computers are not prone to errors if programs are correct. Malfunctions in equipment are often detected automatically, making the avoidance of errors transparent to the user.
Consistency: Given identical data and instructions, the computer will produce the exact same result every time a process is repeated.
Reliability and Fault Tolerance: Many systems are built so that the failure of one component does not cause the entire system to fail.
Memory Capability: Computers can store and access vast volumes of data.
Processing Capability: Modern computers execute millions of instructions per second.

Diverse Areas of Computer Application

Communication: Digital communication replaces older analogue systems. Specific tools include email, Electronic Data Interchange (EDI), Electronic Funds Transfer (EFT), and the Internet.
Banking: Used for credit analysis, fund transfers, customer relations, Automated Teller Machines (ATMs), home banking, and online banking.
Organizational Management: Proliferation of Management Information Systems (MIS) aids in planning, controlling, and decision-making. Examples include transaction processing, sales and marketing, accounting, and customer service.
Science, Research, and Engineering: - Research tools for complex computations. - Simulations for outer-space or flight training. - Diagnostic and monitoring tools. - Computerized mapping via Global Positioning Satellite (GPS) technology. - Mass production in the auto industry using computer-driven tech.
Education: E-learning and virtual classrooms provide global reach. Computers assist in test scoring (e.g., uniform standardized tests), school administration, and computer-aided instruction.
Information Management: Internet reference materials and efficient running of libraries for storage and retrieval.
Manufacturing and Production: Technologies like Computer Aided Design (CAD), Computer Integrated Manufacturing (CIM), and process control systems.
Entertainment: High-quality storage of motion pictures and music on CDs, VCDs, and DVDs. Also includes Internet resources and video games.
Retailing: Point of Sale (POS) systems, credit card payments, and stock inventory management.
Home Appliances: Embedded microprocessors in microwave ovens, clothes washers, refrigerators, and sewing machines for efficiency and economy.
Reservation Systems: Streamlining air travel and hotel bookings, including billing and guest accommodations.
Health Care and Medicine: Used for patient records, medical insurance systems, diagnosis, and patient monitoring.

Historical Progression: The Five Generations of Computers

First Generation (1946 – 1957): - Technology: Vacuum tubes and circuitry of wires. - Speed: Very slow. - Power: High consumption; generated significant heat. - Size: Very large, requiring vast installation space. - Operation: Cumbersome; required manual switching between programs and input/output. - Examples: LEO 1, UNIVAC 1.
Second Generation (1958 – 1964): - Technology: Transistors replaced vacuum tubes. - Advantage: No filament heating required, lower manufacturing costs, and significantly reduced size. - Software: Introduction of high-level languages like COBOL and FORTRAN, and the provision of system software. - Speed: Measured at approx. $200\,KHz$ . - Example: IBM System 1000.
Third Generation (1965 – 1971): - Technology: Integrated Circuits (ICs) involving Small-Scale Integration (SSI). - Improvement: Transistors were previously mounted individually on circuit boards, which was error-prone; ICs consolidated this. - Metrics: Higher processing speeds, larger memory, and lower cost. - Speed: Up to $1\,MHz$ . - Example: IBM System 360.
Fourth Generation (1972 – Present): - Technology: Large-Scale Integration (LSI). More than $1,000$ components can be placed on a single chip. - Speed: Up to $10\,MHz$ . - Example: IBM 4000 series.
Fifth Generation (Parallel Processing / AI): - Technology: Very Large Scale Integration (VLSI) and Ultra Large Scale Integration (ULSI). - Components: Millions of components integrated on one chip. - Innovations: Parallel processing and Artificial Intelligence (AI) to allow computers to make independent decisions. - Speed: $400\,MHz$ and above.

Multi-Dimensional Classification of Computers

By Processing Method: - Digital Computers: Process data in discrete values (0, 1, 2). Highly accurate for business and scientific use. - Analog Computers: Process physical variables and output physical magnitudes as smooth graphs. Used in science and engineering. - Hybrid Computers: Combine digital and analog features for specialized engineering problems.
By Purpose: - Special Purpose: Designed for a specific function (e.g., medicine or manufacturing). - General Purpose: Versatile for various tasks (e.g., word processing and accounting).
By Power and Size (Configuration): - Supercomputers: Largest and most powerful; used for meteorology and astronomy. Examples: Cray, Fujitsu. - Mainframe Computers: Large, expensive systems requiring controlled environments and specialist staff. Used by large commercial organizations. Example: IBM. - Minicomputers: Intermediate speed and size; used as departmental computers. Manufacturers: IBM, ICL. - Microcomputers: Personal computers (PCs) for office/leisure. Includes desktops, laptops, and palmtops. Examples: HP, Compaq, Dell.

Data Representation and Measurement Units

Binary Logic: Data exists as electrical voltages. Since electricity has two states (ON/OFF), binary digits (bits) of "0" and "1" are used.
The Bit: The basic unit of data representation.
The Byte: A group of $8$ bits, typically representing one character (e.g., 'A').
Capacity Abbreviations: - Kilobyte (KB): $2^{10} = 1024$ bytes (approx. $1,000$ bytes). - Megabyte (MB): $2^{20} = 1,048,576$ bytes (approx. $1,000,000$ bytes). - Gigabyte (GB): $2^{30} = 1,073,741,824$ bytes (approx. $1,000,000,000$ bytes). - Terabyte (TB): $2^{40} = 1,099,511,627,776$ bytes (approx. $1,000,000,000,000$ bytes).
Data Formats: - Numerical: Binary system. - Text: ASCII coding scheme. - Program Instructions: Machine language. - Pictures: gif, jpeg, bmp, wmf. - Video: avi, mov, mpeg. - Sound: wav, au, mp3.

Functional and Logical Components of a Digital Computer

System Unit: Houses the internal processing components.
Peripherals: Devices connected to the system unit including: - Input Devices: Enters programs and data. - Central Processing Unit (CPU): Interprets and processes data. - Main Memory: Temporary storage during execution. - Control Unit (CU): Directs the execution of programs. - Arithmetic Logic Unit (ALU): Performs math and logic ops. - Output Devices: Displays processed information. - Storage Devices: Permanent storage for data/programs. - Communication Devices: Connects computers for data exchange.

Hardware: Input and Terminal Systems

Terminals: A point of connection to a host computer or server. - Dumb Terminal: Cannot process data independently; used for input/output only (e.g., airline reservation desks). - Intelligent Terminal: Contains processing unit, memory, and local storage; uses communication software. - Network Terminal (Thin Client): Low-cost; no hard drive; relies on a server for software. - Internet Terminal (Web Terminal): Used primarily at home to display web pages on a TV.
Direct Data Entry Devices: - Pen Input: Light pens used by engineers to modify designs by touching the screen, closing a photoelectric circuit. - Touch Screens: Use infrared beams; used in ATMs, gas stations, and fast-food kiosks. - Scanning Devices: Convert images/characters to machine-readable form. - Image Scanner: Converts physical images to electronic signals. - Fax Machine: Sends image data over phone lines. - Bar-Code Readers: Photoelectric scanners for vertical stripes. - MICR (Magnetic-Ink Character Recognition): Reads magnetic check numbers. - OCR (Optical-Character Recognition): Reads preprinted characters on bills. - OMR (Optical-Mark Recognition): "Mark sensing" used for scoring standardized tests (KCPE, SAT, GMAT). - Voice-Input: Converts speech to digital code via microphones. Useful for hands-free medical dictation or security.

CPU Internal Components and Processing

Clock Speed: Rate of electronic pulses, measured in Megahertz ( $MHz$ ).
Control Unit (CU): Decodes instructions and coordinates the CPU.
ALU: Performs logical comparisons and math.
Registers: High-speed storage for instructions currently being executed.
Bus: Internal highway connecting all components.
Main Memory (Primary Storage): Physically close to the CPU; access time measured in milliseconds ( $ms$ ).

Output Technologies

Printers: - Capacity-based: Character (one at a time), Line (one line at a time), Page (whole page at a time). - Dot Matrix: Striking pins against a ribbon; noisy; lower quality. - Ink Jet: Shooting tiny ink droplets; quiet; good quality; color capable. - Laser Jet: Uses copier technology with toner and laser/LED; excellent quality; quieter than ink jet. - Thermal: Uses heat and sensitive paper; very quiet; uses wax crayons for expensive color models.
Plotters: Specialized for high-quality charts, maps, blueprints, and architectural drawings.
Monitors: For soft-copy output; characterized by size and clarity.
Voice-Output: Stereo speakers or headphones; used in vending machines, cars, and learning tools.

Secondary and Auxiliary Storage Systems

Magnetic Disks: - Floppy Disks: $5\frac{1}{4}$ inch or $3\frac{1}{2}$ inch ( $1.44\,MB$ ). Slow and fragile. - Hard Disks: Capacity $20$ to $120\,GB$ . High speed and durability.
Optical Disks: - CD-ROM: Read-only ( $650\,MB$ ). - CD-R / WORM: Write Once, Read Many ( $650\,MB$ ). - CD-RW: Re-writable ( $650\,MB$ ). - DVD-ROM: High resolution; $4.7\,GB$ to $17\,GB$ .
Magnetic Tapes: Plastic film coated with iron oxide; includes tape cartridges and reels.
Advanced Storage Options: - RAID: Redundant Arrays of Independent Disks; fault-tolerant storage using multiple disks to prevent data loss. - SAN: Storage Area Network; connects servers and storage in a dedicated network. - COM: Computer Output Microfilm; transfers data directly to microfilm to avoid printing costs (used by archives).

Specialized Computer Memory Types

RAM (Random Access Memory): Volatile main memory. Includes DRAM (Dynamic) and SDRAM (Synchronous).
ROM (Read Only Memory): Non-volatile; used for the bootstrap program (startup). - PROM (Programmable ROM): Programmed once; used in alarm systems and video games. - EPROM (Erasable Programmable ROM): Can be erased and reprogrammed; used in robotic controllers.
Cache Memory: High-speed memory located on the processor (L1) or between processor and RAM (L2) for fast retrieval of frequent instructions.
Bubble Memory: Uses magnetic bubbles for 1s and 0s; works in harsh conditions (dust); non-volatile but expensive.
Optical/Holographic Memory: Uses