Class 11 Computer Science – Chapter 1: Computer System

1.1.1 Definition, Characteristics and Application of Computer

The word computer is derived from the Latin word ‘computare,’ which means to calculate. The computer is defined in the Oxford dictionary as, “An automatic electronic device for making calculations or controlling operations that are expressible in numerical or logical terms.”

Definitions of a computer:

• “A computer can be defined as a multipurpose, multi-programmable electronic data processing device that is capable of accepting input, processing it, and providing information as output at a fast speed.”
• “It is an electronic device which can perform computation as well as logical action at an enormous speed.”
• “A computer is an electronic device which takes input data from input devices, stores it, processes it, and produces output.”

Characteristics of a Computer System

1. Speed: A computer can work very fast, performing millions of instructions per second.
2. Automatic: It carries out jobs without human interaction once programmed.
3. Accuracy: A computer performs every calculation with the same accuracy. The term GIGO (Garbage In Garbage Out) applies here.
4. Diligence: A computer is free from tiredness and lack of concentration, capable of doing tasks repeatedly.
5. Versatility: A computer can perform different types of tasks and has wide application areas.
6. Reliability: The results obtained by the computer are very reliable when given correct data.
7. Storage: The computer has in-built memory and can use secondary storage devices.
8. Resource Sharing: Computers can connect with each other to share resources.
9. No Feeling: A computer doesn’t have feelings, emotions, taste, knowledge, or experience.
10. No Intelligence (IQ): A computer cannot do any work without instructions from the user.

Application of Computer System

1. Education: Report cards, attendance records, presentations, online learning.
2. Offices: Typing letters, emails, customer database, presentations, data analysis.
3. Transportation: Online ticket booking, air traffic control, railway reservations.
4. Hospitals: Diagnosis, laboratory tests, patient records management.
5. Bank: Electronic fund transfer, ledger maintenance, transaction handling.
6. Film: Special effects, music composition, video editing.
7. Communications: E-mails, e-fax, internet communication.
8. Hotel Management: Front desk management, personnel management, accounting.

1.1.2 Evolution of Computer Technology

History of Computer System

1. Mechanical Era

2. Electro-mechanical Era

3. Electronic Era

Generation of Computer

The term “generation” indicates the stage of evolution or development of a computer based on the type of technology used in the computer’s construction over a period of time.

Changes in each generation:

• Increased speed
• Increased storage capacity
• Increased reliability
• Reduced size of computer
• Reduced cost of computer
• Reduced heat produced by computer

1. First Generation Computers (1945-1956 AD)

• Vacuum tube is used as the main component
• Magnetic drum for primary memory
• Magnetic tape for secondary memory
• Punch card for input
• Printout display for output
• Limited storage capacity (1KB to 4KB)
• Large in size, expensive
• Operating speed in millisecond range
• Generate large amount of heat
• Examples: ENIAC, EDVAC, UNIVAC, IBM 650, IBM 705

2. Second Generation Computers (1956-1964 AD)

• Transistor is used as the main component
• Magnetic core memory for primary memory
• Magnetic tape for secondary memory
• Use assembly language and high-level language
• Reduced heat generation
• Punch card as input device
• Printout display as output device
• Large storage capacity
• Higher speed than first generation
• Examples: IBM 1401, IBM 730, 400 series

3. Third Generation Computers (1964-1971 AD)

• IC (Integrated Circuit) is used as the main component
• Magnetic disk for secondary storage
• Semi-conductor for primary memory
• Keyboard and mouse as input devices
• Monitor as output device
• Started to use operating system
• High processing speed
• Operation speed in nanosecond range
• Use high-level language for programming
• Examples: IBM 360, IBM 370

4. Fourth Generation Computers (1971 – Present)

• Microprocessor (VLSI) is used as the main component
• Semi-conductor memory for primary memory
• Magnetic disk for secondary storage
• Storage capacity increased drastically (TBs)
• Versatile input and output devices
• High-level and 4GL language for programming
• High-speed microprocessors (Intel-core i3, i5, i7)
• Used microcomputers (laptop, notebook)
• More portable and handheld computer
• Small in size, more reliable, reduced cost
• Very user-friendly
• Examples: IBM PCs, Apple PCs, handheld computers

5. Fifth Generation Computers (Present and Beyond)

• Bio-chip or AI (Artificial Intelligence) as main component
• Input and Output in the form of speech and graphic images
• Able to understand natural languages
• Having their own thinking power
• Having capacity to make decisions
• Large capacity of internal storage
• Still in research phase

1.1.3 Measurement Unit of Processing Speed and Storage Unit

Storage Unit

Processing Speed: Measured in Hertz (Hz), representing cycles per second. Modern processors use Gigahertz (GHz) – billions of cycles per second.

1.1.4 Super, Mainframe, Mini and Microcomputers

Classification of Computer

On the basis of size:

• Supercomputer
• Mainframe computer
• Mini computer
• Micro computer

On the basis of working principle:

• Analog computer
• Digital computer
• Hybrid computer

On the basis of brand:

• IBM PC
• IBM Compatible
• Apple PC

Supercomputer

• Most powerful and fastest computer
• Very expensive (15-20 million dollars)
• Performs more than 1 billion or trillion calculations per second
• Capacity of 40 thousand microcomputers
• Used for weather forecasting, nuclear energy research, aircraft design
• Examples: Cray-1, Cray-2, Param

Mainframe Computer

• Large in size
• Processing speed slower than supercomputer but faster than mini and personal computers
• Very expensive to buy and operate
• Can operate large number of various equipment
• Multiple processors
• Process data at several million instructions per second (MIPS)
• Used in large organizations (banks, airlines, universities)
• Examples: IBM S/390, Control Data Cyber 176, IBM 4381

Mini Computer

• Smaller in size than mainframe
• Lower processing speed and cheaper than mainframes
• Capabilities between mainframe and personal computer
• Handles more than 100 workstations (multi-user)
• Examples: IBM AS/400, Prime 9755, VAX 7500

Micro Computer

• Based on microprocessor
• Smallest general-purpose processing system
• Self-contained unit for one person at a time
• Also known as personal computer
• Very small in size and cost
• Examples: Apple, IBM PC, Laptop, PDA

1.1.5 Mobile Computing and its Application

Mobile computing is a generic term describing one’s ability to use technology while moving, as opposed to portable computers which are only practical for use while deployed in a stationary configuration.

Mobile computing refers to the use of small and portable computing devices in wireless-enabled networks to provide wireless connection to a central main server. These devices include laptops, notebook PCs, tablet PCs, and other handheld devices.

Advantages of Mobile Computing:

• Enables users to work from any location at any time
• Saves time and cost
• Enhanced productivity
• Entertainment
• Data can be transferred easily between users
• Fast processing speed
• Easy to handle and carry small devices

Disadvantages of Mobile Computing:

• Battery consumption hindrance
• Inefficient bandwidth in transmission
• Security issues or threats
• Network instability
• Transmission interferences
• Potential health hazards

Common Applications:

• Communication: Email, messaging apps, video calls
• Navigation: GPS and mapping services
• E-Commerce & Mobile Banking
• Entertainment: Streaming music, videos, mobile gaming
• Social Media access

1.2.1 Concept of Computer Architecture and Organization

Computer Architecture: The structure and behavior of the various functional units of the computer and their interaction. It describes what the computer does and deals with the functional behavior of the computer system. It indicates its hardware.

Computer Organization: It deals with the structural relationship between the input devices, processing part, and output devices. It describes how the computer does it and deals with the structural relationship. It indicates its performance. For designing a computer, the organization is decided after its architecture. It consists of physical units like circuit design, peripherals, and processors.

      +-----------------+      Control Bus
      | Central         |<--------------------->
      | Processing Unit |      Address Bus
      | (CPU)           |<--------------------->
      | - Control Unit  |       Data Bus
      | - ALU           |<--------------------->+-----------------+
      +-----------------+                       | Memory Unit     |
            ^                                   | (RAM)           |
            |                                   +-----------------+
            v
      +-----------------+
      | Input/Output    |
      | Devices         |
      +-----------------+
                    

1.2.2 Components of Computer System

1. Input Device

The input unit provides an interface between the user and the machine for inputting data and instructions into the computer’s memory. The input unit accepts input, converts it into computer-readable format, and provides it for processing and storage. Examples: keyboard, mouse, etc.

2. Central Processing Unit (CPU)

The CPU is like the brain of a computer that organizes and executes instructions. Its primary function is to execute instructions. Besides executing instructions, the CPU controls all other components such as memory, input, and output devices.

Different parts of CPU:

• ALU (Arithmetic Logic Unit): Performs arithmetic and logical functions. Arithmetic operations include addition, subtraction, multiplication, division. Logical operations include comparison, AND, OR, NOT.
• CU (Control Unit): Controls the entire operation of the computer. It directs the movement of electronic signals between main memory and ALU, and between main memory and input/output devices. Acts as the nervous system.
• Register Array: Multiple registers to store data temporarily during program execution. Registers quickly accept, store, and transfer data, instructions, and results being used immediately.

3. Memory Unit

A memory unit is responsible for storing data and instructions either for short or long period of time.

Primary memory: Main memory of computer used for storing data and instructions during processing. Directly accessible to CPU. Expensive, faster for read/write operations, used for small storage capacity. Examples: RAM and ROM.

Secondary memory (auxiliary): Additional memory for computer used for storing huge amounts of data for long period. Cheaper, slower, used for large storage capacity. Not directly accessible to CPU. Examples: Hard disk, pendrive, memory card.

4. Output Devices or Units

The output unit provides the result to the user after processing data. It converts the output into user-understandable format before providing it to users.

Types of output:

• Soft copy output (display in visual, like monitor)
• Hard copy output (prints the output, like printer)

1.2.3 Microprocessor

A microprocessor is the CPU of a computer built on a single chip. It contains the Arithmetic Logic Unit (ALU) to perform calculations, the Control Unit (CU) to direct operations, and Registers for high-speed temporary data storage.

Components of Microprocessor:

• ALU (Arithmetic Logic Unit): Performs all arithmetic and logical operations
• Control Unit (CU): Directs and coordinates all operations
• Registers: High-speed temporary storage locations
• Cache Memory: High-speed memory for frequently used data

1.2.4 Bus System

In computer architecture, a bus is a data communication path inside the computer through which data is transmitted from one part to another of the computer and peripheral devices. It is a set of parallel, distinct wires, serving different purposes, which allows devices attached to it to communicate with the CPU.

Function of system bus:

1. It carries information from one component to another
2. It carries data, address, and control signals
3. One component can interact with other components with help of bus

Types of Bus:

1. Control Bus: Carries control signals. The control signal is used for controlling and coordinating various activities across the computer. Generated from control unit within CPU.

2. Address Bus: Carries memory addresses within the device. Allows CPU to differentiate memory locations within the device. Connects CPU and other peripherals and carries only memory addresses. Unidirectional – bits flow in one direction to peripherals.

3. Data Bus: Transfers data from one location to another across computer. The meaningful data to be sent/received from device is placed on this line. CPU uses data bus to transfer data. May be 16-bit or 32-bit data bus. Bi-directional – data flows in both directions between processor, memory, and peripheral devices.

1.2.5 Primary Memory

Primary memory is also known as system’s memory, main memory, primary storage, or internal memory. It is the working area for computer processor.

Tasks of primary memory:

1. It holds data for processing
2. It holds instructions for processing the data
3. It holds data after it is processed, to be sent to output or storage device

Features of primary memory:

1. Directly accessible to CPU
2. Usually volatile memory, except for ROM
3. Expensive and faster for Read/Write operations than secondary memory
4. Normally used for small storage capacity
5. Not used for storing data permanently
6. Not used for transferring data between computers

Types of Primary Memory:

1. RAM (Random Access Memory)

• Short-term, temporary storage memory
• Called “random” because you can read/store data randomly at any time
• Volatile – retains data only while computer is powered on
• Fastest type of memory
• Stores data currently being processed by CPU

Types of RAM:

• Static RAM (SRAM): Made with flip-flops, used for primary storage. Volatile. More expensive and consumes more power than DRAM.
• Dynamic RAM (DRAM): Used as main memory. Retains information in capacitors for short period. Cheaper, can store more information.

2. ROM (Read Only Memory)

• Long-term internal or permanent storage memory
• Non-volatile – retains data without electricity
• Accessed by CPU
• Pre-written by manufacturer to hold boot instructions

Types of ROM:

• PROM (Programmable ROM): Can be programmed only once and read many times. Non-volatile.
• EPROM (Erasable Programmable ROM): Retains contents until exposed to ultraviolet light, which clears contents for reprogramming.
• EEPROM (Electrically Erasable PROM): Can be programmed and erased by electrical waves in milliseconds.

Cache Memory

Cache memory is special high-speed and expensive semiconductor memory placed between CPU and RAM. Used in CPU so CPU doesn’t have to wait for data.

Most frequently used instructions kept in cache memory. Allows CPU to run faster. Made from static RAM components. 5 to 10 times faster than main memory (RAM).

Types of cache memory:

• Internal Cache: Cache present in CPU
• External Cache: Cache present outside CPU

Cache levels: L1 (smallest, fastest), L2 (larger, slower), L3 (very slow). Multiple levels checked starting with smallest cache first.

1.2.6 Secondary Memory

Secondary memory is also called permanent, external, or stable memory. Accessed indirectly via input/output operations. Slower than primary memory but can save large amounts of data (GBs to TBs). Used for carrying data between computers.

Characteristics of secondary memory:

1. Non-volatile type of computer memory
2. Data stored permanently, even when power is off
3. Magnetic and optical memories
4. Also known as backup memory
5. Slower than primary memory

Types of Secondary Memory:

1. Magnetic Disk: Storage device that uses magnetization process to write, rewrite, and read data. Covered with magnetic coating and stores data in form of tracks, spots, and sectors. Examples: Hard disks, zip disks, floppy disks.

2. Flash Memory: Also known as Flash Storage, non-volatile storage memory that can be written/programmed in units called sectors. Used in consumer storage devices and networking technology. Examples: Mobile phones, USB flash drives, tablet computers.

3. Optical Disk: Electronic storage medium using low-power laser beams to record and retrieve digital data. Low-power laser scanner reads pits, with variations in reflected light intensity converted to electric signals. Examples: CD-ROM, DVD.

4. External Storage Memory Stick: Developed by Sony in 1998. Widely used in digital cameras. Storage capacity ranges from MBs to GBs and TBs. Portable storage medium easily removed from device and accessed by computer.

1.2.7 Input Devices

The devices used to input data to computer are called input devices. The data entry stations or devices are termed as input units.

Types of Input Devices:

1. Keyboard: Standard input device. Data entry platform for computer. Has small processor checking accuracy of data during entry. When key pressed, electrical signal generated determining which key was pressed (encoding).

Types of standard keyboards:

• XT (Extended Technology): 85 keys
• AT (Advanced Technology): 101 keys
• Enhanced Technology: 103 keys

2. Mouse: Handheld hardware input device controlling cursor in GUI. Can move and select text, icons, files, folders.

Types of mice:

• Mechanical mouse
• Optical mouse
• Wireless mouse

3. Scanner: Input device used to enter pictures and documents into computer, saving in different formats.

Components: Data capturing sub-system and image processing sub-system.

Types of scanners:

• Flatbed/Desktop scanner: Most versatile and commonly used
• Sheet-fed Scanner: Document moved, scan head immobile. Like small portable printer
• Handheld scanner: User moves it instead of motorized belt. Lower image quality but useful for quick text capture

4. Joystick: Originally from aviation field (control stick for flight control). Mainly used for computer games, particularly flight simulators.

5. Graphics Tablet: Flat, rectangular, pressure-sensitive input device with stylus. Connected to computer serial port. Used for graphics design, engineering work.

6. Digital Camera: Stores images directly rather than on film. Pictures can be downloaded to computer, manipulated with image editing software, and printed.

1.2.8 Output Devices

The devices from which data is displayed or printed are called output devices.

Types of Output Devices:

1. Monitor/VDU (Visual Display Unit): Displays images generated by computer or electronic device. Standard monitors in personal computers and laptop displays are integrated VDUs.

Technologies: LCD and LED technology

2. Printer: External output hardware device taking electronic data and generating hard copy of document.

Types of Printers:

a) Impact Printer: Head strikes ink-coated ribbon to print information. Noisy, slow, poor quality output. Examples: Dot matrix, Daisy wheel, Golf ball.

b) Non-Impact Printer: Thermal, chemical, or optical techniques applied to print information. Noiseless, fast, high-quality output. Examples: Thermal, laser, ink-jet printers.

Detailed Printer Types:

Dot-matrix printers: Can print both image and text of different fonts and sizes. Appropriate for low volume printing. Three operating modes: fast, medium, slow. Faster speed has lower printing quality.

Laser printer: High-resolution page printer processing entire page at time. Produces high-quality output. Capable of color printouts. Relatively costly. Emits small amount of ozone (hazardous to health).

Ink-jet printer: Non-impact page printer with heads ejecting ink onto paper. High-quality output capable of fine, smooth details. Capable of vivid color printing, good for pictures. Slower than laser printer. Not good for high-volume printing. Print head less durable.

3. Speaker: Common output device used with computer system. Essential for multimedia system. Amplifies sound output.

1.2.9 Hardware Interfaces

A hardware interface/port is socket outside system unit connected to expansion board inside system unit. Port allows connecting peripheral object (monitor, printer, modem) to communicate with computer system.

Function of hardware interfaces:

1. Connecting peripheral devices
2. Transmitting data to and from peripheral devices
3. Providing electrical power to low-power devices (mouse, keyboard)

Popular Hardware Interfaces:

1. Parallel port: Allows line connection enabling 8 bits transmitted simultaneously. Parallel lines move faster than serial but efficient only up to 15 ft. Used for faster speed devices (monitors, printers).

2. Serial port: Enables line connection sending bits one after another on single line. Used for slow-speed devices and equipment not close by.

3. USB (Universal Serial Bus): Serial bus standard to connect devices to computer. Designed to allow many peripherals using single standardized interface socket. Intended to replace many varieties of ports.

Can connect: Mouse, keyboard, joystick, printer, scanner, external HD, digital camera.

History: USB 1.0 introduced in 1994 by Intel, Compact, Microsoft, IBM.