Computer Fundamentals: Introduction to Hardware and Software, Lecture notes of Computer Fundamentals

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Computer

Fundamental

Unit 1

Computer Fundamentals

What is Computer?

Computer is an advanced electronic device that takes raw data as input from the user and

processes these data under the control of set of instructions (called program) and gives

the result (output) and saves output for the future use. It can process both numerical and

non-numerical (arithmetic and logical) calculations.

A computer has four functions:

a. accepts data

b. processes data

c. produces output

d. stores results

Input

Processing

Output

Storage

Input (Data):

Input is the raw information entered into a computer from the input devices. It is the

collection of letters, numbers, images etc.

Process:

Process is the operation of data as per given instruction. It is totally internal process of

the computer system.

Output:

Output is the processed data given by computer after data processing. Output is also

called as Result. We can save these results in the storage devices for the future use.

Computer System

All of the components of a computer system can be summarized with the simple

equations.

COMPUTER SYSTEM = HARDWARE + SOFTWARE+ USER

• Hardware = Internal Devices + Peripheral Devices

All physical parts of the computer (or everything that we can touch) are known as

Hardware.

• Software = Programs

Software gives "intelligence" to the computer.

• USER = Person, who operates computer. Computer Fundamentals - 2 -

13. Magnetic

Ink

Character

Reader

(Used in

Bank)

15. Magnetic

Card

Reader

(Used in

Shops,

Colleges,

Stations etc)

17. Bluetooth

14. Optical

Mark

Reader

(Used for

Answer

Sheet

Marking

Purpose)

16. Biometric

Devices

Computer Fundamentals - 4 -

Processor

CENTRAL PROCESSING UNIT (CPU)

The main unit inside the computer is the CPU. This unit is responsible for all events

inside the computer. It controls all internal and external devices, performs arithmetic and

logic operations. The CPU (Central Processing Unit) is the device that interprets and

executes instructions.

Output Devices

1. Monitor

3. Projector InkJet

4. Plotter

5. Speaker

Laser

2. Printer

(Dot

Matrix)

Computer Fundamentals - 5 -

B. Optical

disk

C. Pen Drive

D. Zip

Disk

(super

disk)

E. Floppy Disk

F. Memory

Cards

G. External

Hard Disk

Peripheral Devices

1. The

Modem/

Internet

Adapter

3. Router

4. TV Tuner

Card

2. Switches/H

ub

Computer Fundamentals - 7 -

Tel: 02085197362 E-mail: admin@sclondon.co.uk

Internal Components

1. The Mother 2. Expansion

Board

3. CMOS

Battery

5. Network

Card

4. Cooling

Fan

6. Graphics

Card

Slots

7. Power Supply

Unit (SMPS)

8. Memory

Slots

Software

Software, simply are the computer programs. The instructions given to the computer in

the form of a program is called Software. Software is the set of programs, which are used

for different purposes. All the programs used in computer to perform specific task is

called Software.

Types of software

1. System software:

a) Operating System Software

DOS, Windows XP, Windows Vista, Unix/Linux, MAC/OS X etc.

b) Utility Software

Windows Explorer (File/Folder Management), Windows Media Player, Anti

Virus Utilities, Disk Defragmentation, Disk Clean, BackUp, WinZip, WinRAR

etc...

Computer Fundamentals - 8 -

1. Thermometer

3. Petrol Pump

Indicator

4. Multimeter

2. Speedometer

b) Digital Computer

A computer that performs calculations and logical operations with quantities represented

as digits, usually in the binary number system.

c) Hybrid Computer (Analog + Digital)

A combination of computers those are capable of inputting and outputting in both digital

and analog signals. A hybrid computer system setup offers a cost effective method of

performing complex simulations.

Computer Fundamentals - 10 -

On the basis of Size

a) Super Computer

The fastest type of computer. Supercomputers are very expensive and are employed for

specialized applications that require immense amounts of mathematical calculations. For

example, weather forecasting requires a supercomputer. Other uses of supercomputers

include animated graphics, fluid dynamic calculations, nuclear energy research, and

petroleum exploration.

The chief difference between a supercomputer and a mainframe is that a supercomputer

channels all its power into executing a few programs as fast as possible, whereas a

mainframe uses its power to execute many programs concurrently.

b) Mainframe Computer

A very large and expensive computer capable of supporting hundreds, or even

thousands, of users simultaneously. In the hierarchy that starts with a simple

microprocessor (in watches, for example) at the bottom and moves to supercomputers at

the top, mainframes are just below supercomputers. In some ways, mainframes are more

powerful than supercomputers because they support more simultaneous programs. But

supercomputers can execute a single program faster than a mainframe.

c) Mini Computer

A midsized computer. In size and power, minicomputers lie between workstations and

mainframes. In the past decade, the distinction between large minicomputers and small

mainframes has blurred, however, as has the distinction between small minicomputers

and workstations. But in general, a minicomputer is a multiprocessing system capable of

supporting from 4 to about 200 users simultaneously.

Computer Fundamentals - 11 -

e) Workstations

A terminal or desktop computer in a network. In this context, workstation is just a

generic term for a user's machine (client machine) in contrast to a "server" or

"mainframe."

On the basis of Brand

a) IBM/IBM Compatible Computers

c) Apple/Macintosh

Booting

The process of loading the system files of the operating system from the disk into the

computer memory to complete the circuitry requirement of the computer system is called

booting. The system files of MS. DOS are:

Types of Booting:

There are two types of booting:

• Cold Booting: If the computer is in off state and we boot the

computer by pressing the power switch ‘ON’ from the CPU box

then it is called as cold booting.

Computer Fundamentals - 13 -

Warm Booting: If the computer is already ‘ON’ and we restart it by pressing

the ‘RESET’ button from the CPU box or CTRL, ALT and DEL key

simultaneously from the keyboard then it is called warm booting.

How to start the Computer in Ms. Windows mode?

There is nothing special you need to start this system. Just,

1. Switch ON the Power Supply.

2. Switch ON the CPU and,

3. Switch ON the Screen (Monitor).

How to Shutdown (Turn Off) the Computer?

Before shutting down the Computer, close all opened windows at first. Then,

1. Click on Start button.

2. Click on Shutdown (Turn Off Computer).

Then, Computer asks you:

What do you want the Computer to do?

• Standby
• Shutdown (Turn Off)
• Restart
• Restart in MS-DOS mode. Turn off computer s ® ® Stand By TurnOff Restart

Note: The options will be different from one OS to another.

3. Choose 2nd option (i.e. Shutdown/Turn Off).

4. Click on OK.

Then, wait until the message “It’s now safe to turn off your Computer”.

5. Then, Switch Off the screen.

6. Switch Off the CPU.

7. At last, Switch Off the power supply.

Computer Fundamentals - 14 -

different models, each representing a different type of organization, depending on the cost, physical size

and technology used.

In this chapter, we shall discuss in detail the functioning of the central processor of a computer system,

how the processor communicates with the memory and input/output devices, and the instruction sets used

in the design of processors.

2.2 CENTRAL PROCESSING UNIT

The function of any computer system revolves around a central component known as central processing

unit (CPU). The CPU, which is popularly referred to as the “brain” of the computer, is responsible for

processing the data inside the computer system. It is also responsible for controlling all other components of

the system. Figure 2.1 shows a typical block diagram of the computer system, illustrating the arrangement

of CPU with the input and output units as well as the memory of the computer system.

| Main Memory Unit A Stores and retrieves Input Unit Sends data data and instructions Receives results Output Unit Fig. 2.1 The block diagram of a computer system

The main operations of the CPU include four phases:

• Fetching instructions from the memory.
• Decoding the instructions to decide what operations to be preformed.
• Executing the instructions.
• Storing the results back in the memory.

This four-phase process is known as the CPU cycle, which is illustrated in Fig. 2.2.

As shown in the Fig. 2.1, the central processing unit consists of the following subsystems:

• Arithmetic Unit (AU)
• Logic Unit (LU)
• Control Unit (CU)

The CPU makes use of the following memory subsystems for carrying out its processing operations:

• Main Memory Unit
• Cache Memory
• Registers

2.2.1 Arithmetic Unit

Arithmetic Unit (AU) is a part of the CPU that performs arithmetic operations on the data. The arithmetic

operations can be addition, subtraction, multiplication or division. The multiplication and division

operations are usually implemented by the AU as the repetitive process of addition and subtraction

operations respectively. Some CPUs contain separate AUs for integer or fixed-point operations (integers)

and real or floating-point operations (real/decimal). AU takes the input in the form of an instruction that

contains an opcode, operands and the format code. The opcode specifies the operation to be performed

and the operands specify the data on which operation is to be performed. The format code suggests the

format of the operands, such as fixed-point or floating-point. The output of AU contains the result of the

operation and the status of the result, whether it is final or not. The output is stored in a storage register by

the AU. Register is a small storage area inside the CPU from where data is retrieved faster than any other

storage area.

2.2.2 Logic Unit

Logic Unit (LU) is a part of the CPU that performs logical operations on the data. It performs 16

different types of logical operations. The various logical operations include greater than (>), less than (<),

equal to (=), not equal to (A), shift left, shift right, etc. LU makes use of various logic gates, such as AND,

OR, NOR, etc for performing the logical operations on the data.

2.2.3 Control Unit

Control Unit (CU) is an important component of CPU that controls the flow of data and information.

It maintains the sequence of operations being performed by the CPU. It fetches an instruction from the

storage area, decodes the instruction and transmits the corresponding signals to the AU or LU and the

storage registers. CU guides the AU and LU about the operations that are to be performed and also suggests

the I/O devices to which the data is to be communicated. CU uses a program counter register for retrieving

the next instruction that is to be executed. It also uses a status register for handling conditions such as overflow

of data.

2.2.4 Main Memory Unit

The main memory is referred to as the internal memory or primary memory of the computer. It is also

known as Random Access Memory (RAM). It is a temporary storage medium that holds the data only

for a short period of time. Once the computer is switched off, the data stored in the RAM gets erased.

The memory space of RAM is limited and therefore all the files and instructions cannot be stored in it.

These files and instructions are normally stored in a different location known as secondary storage and are

copied from there to the RAM before execution. This technique is referred as swapping. The memory space

available in RAM also affects the speed of a computer system. If the memory space is more, more number

Figure 2.4 shows the communication between the processor and the memory of the computer system.

Fig. 2.4 Processor to memory communication

The processor can interact with the memory of the computer system for reading data from the memory

as well as for writing data on to the memory. The MAR and MBR registers play a very important role in implementing

this type of communication. These registers are the special-purpose registers of the processor.

MAR is used by the processor to keep track of the memory location where it needs to perform the reading

or writing operation. This register actually holds the address of the memory location. On the other hand, the

Memory Data Register (MDR) is used by the processor to store the data that needs to be transferred from/to

the memory of the computer system. The reading and writing operations performed by the processor are

called memory read and memory write operations.

Figure 2.5 illustrates the memory read operation performed by the processor of the computer system.

The processor performs the following steps to read the data from the desired memory location:

Fig. 2.5 Illustrating the memory read operation

1. First, the processor loads the address of the memory location from where data is to be read into the

MAR register, using the address bus.

2. After loading the address of the memory location, the processor issues the READ control signal

through the control bus. The control bus is used to carry the commands issued by the processor, and

the status signals are generated by the various devices in response to these commands.

3. After receiving the READ control signal, the memory loads the data into the MDR register from the

location specified in the MAR register, using the data bus.

4. Finally, the data is transferred to the processor.

The memory write operation helps the processor to write the data at the desired memory location.

Figure 2.6 illustrates the memory write operation performed by the processor of the computer system.

The processor performs the following steps for writing the data at the desired memory location in the

computer system:

1. First, the processor loads the address of the memory location where data is to be written in the MAR

register, using the address bus.

2. After loading the address of the memory location, the processor loads the desired data in the MDR

register, using the data bus.

3. After this, the processor issues the WRITE control signal to the memory, using the control bus.

4. Finally, the memory stores the data loaded in the MDR register at the desired memory location.

2.3.2 Processor to I/O Devices Communication

The communication between I/O devices and processor of the computer system is implemented using an

interface unit. In a computer system, data is transferred from an input device to the processor and from

the processor to an output device. Each input and output device in the computer system is provided with

a controller, called device controller. The device controller is used to manage the working of various

peripheral devices. The processor actually communicates with the device controllers of the various I/O

devices for performing the I/O operations.

Figure 2.7 illustrates how the communication between the processor and the I/O devices of the computer

system is implemented. The interface unit acts as an intermediary between the processor and the device

controllers of various peripheral devices in the computer system. The basic function of the interface unit is

to accept the control commands from the processor and interpret the commands so that they can be easily

understood by the device controllers for carrying out necessary operations. Therefore, we can say that

the interface unit is responsible for controlling the input and output operations between the processor and

the I/O devices. The interface unit contains data register and status register. The data register is used to

store the data to be transferred, either to the processor or to an output device. The status register is used

to indicate the status of the data register, i.e., whether it is currently holding the data or not. If the data

register is holding the data to be transferred, the flag bit of the status register is set to one. The processor

to I/O devices communication involves two important operations, i.e., I/O read and I/O write. The I/O read

operation helps the processor to read the data from an input device.

Fig. 2.7 Illustrating the communication process between the processor and I/O devices

Figure 2.8 illustrates how the data is transferred from an input device to the processor of the computer

system. The steps performed while transferring the data from an input device to the processor are:

1. The data to be transferred is placed on the data bus by the input device, which transfers single byte of

data at a time.

2. The input device then issues the data valid signal through the device control bus to the data register,

indicating that the data is available on the data bus.

3. When the data register of the interface unit accepts the data, it issues a data accepted signal through

the device control bus as an acknowledgement to the input device, indicating that the data has been

received. The input device then disables the data valid signal.

4. As the data register now holds the data, the F or the flag bit of the status register is set to 1.

5. The processor now issues an I/O read signal to the data register in the interface unit.

6. The data register then places the data on the data bus connected to the processor of the computer

system. After receiving the data, the processor sends an appropriate acknowledgement signal to the

input device, indicating that the data has been received.