Chapter 1 : Computer System

Introduction

The word "computer" comes from the Latin word "computare" which means to calculate. So a computer is normally considered to be a calculating device that can perform arithmetic operations at fast speed.

Definition

In simple terms, any electronic machine that can perform IPOS (Input Process Output Storage) cycle is known as computer.

An electronic device which accept raw data, process the data, stores the data for future use and gives the desired information (result) as output, such a device which have memory is called computer.

Characteristics of Computer

Following are some of the features of a digital computer:

1. Speed — Computer can calculate very complex data at a very fast rate that human being may not be able to do. The speed of the computer is measured in terms of fraction of second.

2. Diligence — It Means, is absolutely free from physical tiredness and mental fatigue. Because a computer has maximum capacity to perform any kind of tasks repeatedly at the same level of timing periods.

3. Versatile — Computers have multi-purpose capacities. A computer can do any types of jobs at the same time. That's why computers are versatile devices. At the same level of period of timings, it provides loading an environment to run many of tasks as we needed.

4. Reliability — It is the most recent demand and means in real life of all human beings. Men are imperfect but it has capable to make copy from them. So the modern age is depending onto it because of its capabilities a lot.

5. Automatic — Computer is an automatic machine. Everything that is given to computer are processed and done by computer automatically according to the instructions provided.

6. Accuracy — The result of the computer is 100% accurate if the input data are correct.

7. Storage Capacity — Computers have data storage devices. It stores the data permanently or temporarily. There are mainly two types of storage devices (Primary and Secondary). The capacity of the storage is measured in terms of bytes. The small unit is bit (0 or 1). Computers stores the data form of bit.

8. Word Length — A computer can process 16 bits, 32 bits and 64 bits data at a time. The number of bits the computer can process at a time known as word length.

Application (Use) of Computer

Capability and Limitation

Advantages and Disadvantages of Computer

Advantages

1. Computer is faster than human being and any other devices ever invented.
2. It is always accurate and reliable than human.
3. It is versatile i.e. master in all types of work and fields like education, hospital, banks etc.
4. It can be used for communication among many users.
5. It never feels exhausted and tired as human being.

Disadvantages

1. Computer can be used for computer crimes like hacking, creating and sending viruses, etc.
2. It has increased dependency on machine.
3. It is still expensive so each and every people cannot afford the computer.
4. Repair and maintenance is required frequently.
5. Skilled manpower is required to work in the computer.

History of Computer

Generation of Computer

The advancement in Hardware technology with the span of time is termed as Computer generation. Or the development of the computer took place a stage and each stages is called the generation of computer. There are Five Generations:

First Generation (1945–1955)

Second Generation (1956–1965)

Third Generation (1964–1971)

Fourth Generation (1971–At Present)

Fifth Generation (Future)

Types of Computer

Classification of Computers

On The Basis of Operation

Analog Computer — The computer which can process analog quantities (continuous data) is called an analog computer. It is specially designed to compute physical forces such as temperature, pressure etc. Presley is an example of analog computer.

Digital Computer — The computer which works on discrete data (discontinuous data, binary system or 0 or 1) is known as digital computer. For Example, IBM PC, IBM compatible, Apple/Mac. computer etc.

Hybrid Computer — A Computer, which has combined features of both analog and digital, is known as hybrid computer. It can convert data from analog to digital and digital to analog. These computers are used for scientific research and hospitals. Some of the characteristics of Hybrid Computer are:

• It is a combination of qualities of analog as well as digital computers.
• It can process both continuous and discrete data.
• It has capability to convert one type of data into another.
• It is the special purpose machine.
• It usually has high cost compared to analog and digital computer.

Difference Between Analog and Digital Computer

On the Basis of Size

Super Computer

• Most powerful and fastest digital computer
• Special purpose computer
• Performs billions of instructions per second
• Computing capacity equal to 40,000 microcomputers
• Uses parallel processors
• Requires large space
• Requires temperature-controlled room
• Uses: weather forecasting, scientific research, satellite communication, nuclear research, molecular modeling, study of DNA structure
• Examples: CRAY X-Mp/24, PARAM, ANURAG, etc.

Mainframe Computer

• High processing power but lacks flexibility
• Designed for large-scale data processing
• Large in size, occupies about 1000 sq. ft. area
• Supports more than 100 terminals
• Used in banks, insurance companies, airlines, railway reservation systems
• Also used in networked systems
• Examples: IBM 1401, ICL 2950/10, ICL 39, CYBER 170, etc.

Minicomputer

• Smaller in size and cost compared to mainframe computer, hence called mini computer
• First released in the 1960s
• Capabilities lie between mainframe and microcomputer, so also called midrange computer
• Supports about 50 terminals
• Used in small business organizations, industries, universities, banks, etc.
• Examples: Prime 9755, VAX 7500, HCL, MAGUM, etc.

Micro Computer

• Based on microprocessor
• Small, low cost digital computer
• Requires small space — can be placed on table or kept inside a briefcase
• Has CPU on a single chip
• Used in office, house, school, shop, store
• Smallest types: laptop, notebook, palmtop, PDA
• Examples: IBM PC, Apple/Macintosh

Categories of Microcomputer

Microcomputers are divided into two categories:

• Non-portable category
• Portable category

A. Non-Portable Category

1. Personal Computer (PC)

• Small computer, fits on normal-sized office table
• Designed for use by one person at a time
• Most common computer
• Found in office, college, home, hospital, shops

2. Workstation Computer (WC)

• 5 to 10 times faster than PC
• Larger main and backup memory
• Larger, high-resolution monitor
• Accelerated graphics handling capability
• Suitable for architectural/engineering design, modeling, animation, video editing

B. Portable Category

1. Laptop

• Portable, easy to carry
• Suitable for people on the move
• Lightweight, has all basic features of a computer
• LCD (Liquid Crystal Display) monitor
• Can operate on AC or DC (battery) power, or both

2. Notebook

• Designed for people on the move
• Smaller in size compared to laptop
• Reduced keyboard, screen, functionality, and software support

3. Tablet PC

• Looks similar to laptop/notebook but more convenient
• Differs in accessories, screen, software used
• Allows writing directly on screen using a pen instead of keyboard
• Has handwriting recognition software that digitizes handwritten text

4. Palm Top

• Portable PC, size of a palm
• Very small memory and features compared to laptop/notebook
• Used for storing phone numbers, addresses, pictures, small data
• Has electronic writing pad and light-sensitive electronic pen for input

5. PDA (Personal Digital Assistant)

• Limited in tasks it can perform
• Modern PDAs include: colored screen, scientific calculator, digital diary (phone numbers/addresses), web browser, cell phone, audio-video, games

Concept of Computer Architecture and Organization

• The design, arrangement, construction or organization of the different parts of a computer system is known as Computer Architecture.
• It is the conceptual design and fundamental operational structure of a computer system.
• It is a framework and functional description of requirements and design implementations for the various parts of a computer, focusing largely on the way by which the CPU performs internally and accesses addresses in memory.
• Computer Organization refers to the operational units and their interconnections that realize the architecture specification.
• Computer organization deals with physical aspects of computer design, memory and their types as well as the microprocessor design.

Components of Computer System

A computer system consists of the following components:

1. Input Hardware

• Most computers cannot accept data in human forms like speech or handwriting
• Data must be presented in a way that is easily convertible into electronic form
• Commonly done by typing data into a keyboard, which converts it into machine-sensible form
• Keyboard is just one of many input devices
• In some cases, machine-readable documents or media are produced as part of the input process

2. Output Hardware

• Provides processed results to the user
• Result is taken from main storage and fed to an output device
• Two forms of output:
  • Hardcopy output: Printed form (via printer)
  • Softcopy output: Displayed on monitor screen (like a TV screen)

3. Processing Hardware

• Instructions are obeyed and necessary arithmetic operations carried out on data
• Arithmetic-Logical Unit (ALU):
  • Performs arithmetic and logical operations
  • Usually not a physically separate component (same for control unit)
  • Operations occur at very high speed (e.g., millions of numbers summed in under a second)
• Control Unit:
  • Controls the operation of the computer
  • Fetches instructions from main storage
  • Interprets instructions
  • Issues necessary signals to system components
  • Directs all hardware operations needed to obey instructions

4. Storage Hardware

• Data and instructions are stored and held until needed for processing
• Instructions dictate what actions are to be taken on data
• Results of actions are held until required for output

Fig. Elements of computer system showing logical structure

Microprocessor

Basic Concepts

• Multipurpose, programmable, clock-driven, register-based electronic component
• Fabricated on a single IC (Integrated Circuit) chip
• Capable of performing Arithmetic and Logical Unit (ALU) operations
• Communicates with other connected components
• General purpose device, applicable to a wide range of applications
• Reads binary instructions from an input device or primary memory
• Accepts binary data as input, processes data according to instructions, provides results as output
• First microprocessor: Intel 4004 developed by Intel Corporation in 1971
• Functions like an "artificial brain"

Functions of the Microprocessor

• Carries out processing instructions in and out (fetch) from main memory
• Gives commands to all parts of the computer system
• Controls the sequence of operations
• Controls the storage of data or instructions
• Performs arithmetic calculations (addition, subtraction, etc.)
• Supervises and controls I/O (Input/Output) devices, in addition to execution

Clock Speed

• Every microprocessor/CPU contains a clock along with the Control Unit (CU)
• Clock generates the speed at which instructions are executed
• Synchronizes all components of the computer
• Also known as Clock Rate
• Measured in Megahertz (MHz) or Gigahertz (GHz)
  • 1 MHz = 1 million cycles per second
  • 1 GHz = 1 billion cycles per second
• Greater the speed → more instructions performed
• Today's PCs: clock speeds up to 5 GHz

Problem with High Clock Speed: High clock speed generates heat due to friction, which can damage the microprocessor chip.

Word Length

• Number of bits a processor can process in a single instruction
• Also called word size
• Determines:
  • Amount of RAM that can be accessed
  • Total number of pins on the microprocessor
• Higher word size → faster CPU instruction execution
• Word length ranges from 4 bits to 64 bits (depending on type of microcomputer)
• Most current microprocessors use 32-bit or 64-bit architecture

Components of Microprocessor

The microprocessor consists of mainly three components:

1. Arithmetic Logic Unit (ALU)
2. Control Unit (CU)
3. Register Array (Set of Registers)

1. Arithmetic and Logic Unit (ALU)

• Performs mathematical computations and logic operations
• Controls the speed of these operations as directed by the CU
• Also executes comparisons and logical testing

Calculations performed by ALU:

• Addition, subtraction, multiplication, division
• Logical operations: AND, OR, XOR, NOT
• Increment and decrement
• Left or right shift (content of accumulator shifted left/right by one bit)
• Clear (content of accumulator or carry flag made zero)
• Exponential, logarithmic, trigonometric, and floating-point operations

2. Control Unit (CU)

• Controls the entire operation of the computer
• Receives signals from CPU to move data between microprocessor, memory, input, and output devices
• Acts as the nerve system of the computer system
• Consists of multiple components: Decoder, Flag, Quartz crystal, Control logic circuits

Functions of the Control Unit:

1. Controls and coordinates sequence of data movements around ALU, registers, memories, input and output devices
2. Fetches instructions from memory, decodes and interprets them, and executes the task
3. Issues control signals that control hardware components within the CPU
4. Gives orders to ALU and directs operation of the whole computer system
5. Generates timing/clock speed to count the instruction cycle of the computer
6. Provides status of every device connected to the computer to check its functionality
7. Receives external instructions/commands and generates a sequence of control signals

3. Register Array

• Registers = temporary data holding places in the microprocessor
• Small amounts of high-speed memory contained within the CPU
• CPU contains multiple registers for program execution
• Used to handle movement of information between various units of the computer and to speed up processing
• Most CPUs today have 32-bit or 64-bit registers

Registers are needed during processing for:

• Address of the next instruction to be executed
• Current instruction being decoded
• Results of calculations of frequently used small amounts of data

Functions of Common Registers

Bus System

A bus is a collection of wires, chips, and slots inside the computer through which data is transmitted from one part of the computer to another. Often compared to a highway — pathways on which data travels. It is a set of parallel distinct wires, serving different purposes, allowing devices to communicate with the CPU.

Functions of the Bus:

• Carries information from one component to another
• Carries data, address, or control signals
• Allows one component to interact with others

Types of Bus

Fig. Bus System