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