Chapter 1: Introduction to Computer

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Definition

• A computer is an electronic device, operating under the control of instructions provided by the user that is stored in its own memory which accepts data (input), processes the data accordingly to specified rules, gives out information (output ) and stores data for future use.
• A programmable electronic device that can store. retrieve and process data.
• The word computer comes from the Latin word 'Compute' which means calculate.

Functions of a Digital Computer

•  Takes data as input
• Store data/instructions in the memory and use them when required.
• Process the data and convert them into useful information.
• Generate output and 
• Control the above four operations.

• Block Diagram of a Computer

  

  
  
  

  
  

Characteristics of a computer 

1. Word Length

• It is defined as the unit of information that the computer can process or transfer at a time.
• The word length or the word size of a computer is in the power of 2 for eg: 8 bits, 16 bits, 32 bits, 64 bits and so on.
• A computer with the word length 64 bits is also known as 64 bits computer.
• Usually, the defined bit length of a word is equal to the width of the computer's data bus so that a word can be moved in a single operation from storage to a processor register.

2. Speed

• The computer can process 50 million or more instructions in one second.
• Two factors that determine the speed of a computer are the amount of data the CPU can process and CPU's clock speed.
• The faster the clock, the more the instructions CPU can execute per second.
• A 3.2 GHz processor has a clock speed that beats 3.2 Billion times per second. Each clock beat represents an opportunity for the processor to manipulate several bits equivalent to its capacity - 64 bits can work on 64 bits at a time.

3. Storage

• It can hold and store information both temporarily and permanently and can be internal or external to a computer server or any similar computing devices.

4. Versatility

• A computer can perform different types of tasks with the same ease or same time.

5. Accuracy

• The accuracy of a computer depends on the instruction set and processor type.

6. Diligence

• It is the state in which one can do certain work without feeling tired.

Types of Computer

1. Micro Computers

• A microcomputer is a computer which has a microprocessor as its CPU.
• Eg:- Desktop, Palmtop, Laptop, etc

2. Mini Computers

• It is a computer which is powerful than microcomputers and less powerful than mainframe computers.
• Eg:- Apple MAC Mini and HP Studio Hybrid.
• They contain one or more microprocessors.

3. Mainframe Computers

• They are large computers which have one to hundred processors.
• A mainframe computer can handle thousands of processing needs at time.
• But they lack versatility. Most mainframes can only perform one specific set of tasks.
• Eg:- ATM, IBM z series, etc.

4. Super Computers

• Supercomputers are the most powerful computers made and physically large too.
• They can process a large amount of data and can perform trillion calculations per second.
• They are used to handle large and complex calculations.
• They are used in Weather Forecasting, Nuclear Fission, Quantum Mechanics, etc.
• Eg:- Cray 1, Cray XMP-14

Computer Applications

1. Business
2. Banking
3. Military
4. Education
5. Marketing
6. Medical
7. Meteorology
8. Engineering
9. Communication
10. Sports
11. Entertainment

Central Processing Unit ( CPU )

• CPU is considered as the brain of the computer.
• It is simply known as the processor.
• It controls all the parts of a computer.
• CPU performs all types of data processing.
• CPU fetches information, decodes them and executes the, in sequence.
• It is linked with various peripheral devices such as mouse, keyboard, etc.
• In modern computers the CPU is contained on an integrated circuit chip called a microprocessor mounted on a motherboard.   

Three Components of CPU are:-

1. Arithmetic Logic Unit ( ALU )

• It performs arithmetic and logical calculations.
• The CPU tells the ALU what to perform and then the output is stored in an output register.
• It has two sections:

     a) Arithmetic Section

• This section performs arithmetic calculations like addition, subtraction, multiplication and division.
• All complex calculations are performed by repetitive use of the above operations.

     b) Logic Section

• This section performs logical operations such s ANDing, ORing, comparing, selecting, matching and merging data.

Diagram of ALU

2. Control Unit ( CU )

• This unit controls all the operations of the computer but does not carry out any actual data processing operations.

Functions of CPU are:-

1. It tells the computer's memory, ALU and input/output devices how to respond to the instructions.
2. It is responsible for transferring data and instructions among other units of a computer system.
3. It manages and coordinates all the units of the computer via control and timing signals.
4. It obtains the instructions from the memory, interprets them and directs the operation of the computer.  

Simple diagram of CU

3. Memory unit 

Factors affecting the speed of processor 

1. Clock speed
2. Data Bus Capacity
3. Addressing Mode
4. Register Size ( Register ===> Group of Flip Flops / Each Flip Flop = 1 bit )
5. Instruction Set

System Bus

• It is an electrical line or wires that carry computer signals.
• The amount of data that a bus can carry at one time is called a bus width.
• A bus width with 64 lines can carry 8 bytes of data.

Input Devices 

1. Keyboard
- Commonly 104 Keys

2. Mouse

3. Microphone

• It takes input in human sounds then it is stored in digital form.
• It is a transducer that converts sound to electrical energy.
• It is used in VOIP, Computer Gaming, etc

Output Devices

4. Plasma Displays

Working Principle - https://www.youtube.com/watch?v=Blhj9GmxJQQ

Advantages 

• No Polarizer required
• Thinner and Lighter
• Better viewing angle
• It has richer color change

Disadvantages

• Expensive
• Not suitable for screen sizes under 32 inches. 

5. Printers

a) Impact Printers

• They are printers that print the character by striking a hammer or pin against a ribbon.
• Eg:- Dot Matrix Printer

b) Non- Impact Printers

• It uses chemical, heat or electrical signal to print.
• Eg:- Laser Printer, InkJet Printer, etc

1. Dot Matrix Printers

• Prints one character at a time in the form of dots.
• Speed - 30 to 500 characters per second ( CPS )
• Less Expensive and less energy-consuming
• Noisy and Low Resolutions

2. Inkjet Printers

• High-Quality Prints
• Speed - 40 to 300 CPS
• Resolution - 300 dpi
• Advantages are low initial costs, Shorter Delay and Improved Quality
• Disadvantages are Expensive

3. Laser Printers

• Resolutions - More than 600 dpi 
• 500 - 1000 pages per min.
• Advantages are high speed and good resolution
• Disadvantages are expensive and health hazard.

Difference Between

1. Primary and Secondary storage

2. RAM and ROM

3. SRAM and DRAM

4. System Software and Application Software

Types of ROM

1. PROM ( Programmable Read Only Memory )

• PROM is a read-only memory that can be modified only once by the user.
• Small fuses which are burnt open while programming.
• It can only be programmed once and it cannot be erased.

2. EPROM ( Erasable Programmable Read Only Memory )

• In EPROM one can program the memory chip and erase it a thousand times.
• Used in prototype.
• UV-EPROM uses UV rays to erase.
• Can't be erased when in the system board.
• It takes about 20 min to erase.

3. EEPROM ( Electrically Erasable Programmable Read Only Memory )

• In EEPROM the data can be erased instantly electrically.
• In EEPROM desired bytes can be erased.

Cache Memory

• Very High-Speed Semi-Conductor Memory.
• It acts as a buffer between the CPU and main memory.
• It holds data that are frequently used by the CPU.
• 3 Levels of cache are L1, L2, and L3
• L1 is nearest t the processor.
• L3 is farthest away from the processor.
• It is expensive and volatile.

Secondary Memory Types

1. Sequential Access Secondary Memory

 - Eg: Hard Disks, CD-ROMs and Magnetic tapes

2. Direct Access Secondary Memory

 - Eg: Data Cells, Flash Memory, and Magnetic Drums

Computer Storage

1. Magnetic Tapes

• It records by converting electrical audio signals to magnetic energy.

2. Hard Disk

• Magnetism is used.
• 1's and 0's are used to store data where 1 means magnetized and 0 means demagnetized.

3. Optical Disks

• It also stores data in 1's and 0's using laser beams to make lands and pits on the surface of the disk.
• 1 means Land and 0 means Pits.

4. CD ( Compact Disk )

• It functions as same as an optical disk.
• Its wavelength is 780 nanometres.
• It has less space compared to DVD's

5. DVD ( Digital Video Disk )

• It uses a red laser.
• Its wavelength is 650 nanometres.
• It has more space compared to CD's

6. Blue- Ray Disc

• Blue- Ray is used to store data.
• Its wavelength is 450 nanometres.
• Its capacity is about 50 GB

Note: Less wave-length means more storage space. 

System Software

Operating System

• OS is the interface between Software and Hardware
• OS is an integrated software that is used to manage the overall resources and operations of a computer system.
• Eg: Linux, Mac OS, Windows, etc.

Features of Operating System

1. Program Execution 
2. File Management
3. Memory Management
4. Device Management
5. Security
6. Job Accounting / Task Management
7. Network Communication
8. Processor Management

Utility Programs

• It only performs a specific task.
• Eg:- Antivirus, Disk Repair, Networking Programs, etc.

Application Software

• A variety of tasks can be performed with one software.
• Eg:- MS Word, VLC Media, Spreadsheet, etc
Read-Only Read-Only

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