Operating System

Module 1 :- Computer Fundamentals

Module 2 :- Introduction to Operating System

Module 3 :- Process Management

Module 4 :- Memory Management

Module 5 :- File & Storage Management

1. Computer Fundamentals

Q1: What is Computer?

Ans: A computer is a machine that can be programmed to carry out sequences of arithmetic

or logical operations automatically. Modern computers can perform generic sets of

operations known as programs. These programs enable computers to perform a wide range

of tasks.

Q2: What is Computer Architecture?

Ans: computer architecture is a set of rules and methods that describe the functionality,

organization, and implementation of computer systems. The architecture of a system refers

to its structure in terms of separately specified components of that system and their

interrelationships.

Q3: What are the differences between Computer Architecture and

Computer Organization?

Ans:

Q4: What are the functions of computers?

Ans:

Functions of computers:

i)Input Function

ii)Processing Data

iii)Storing Data

iv)Output Function

i)Input or inserting data and instructions:Data input is the most basic function of a

computer. It's what allows you to transfer information into the system via a mouse,

keyboard, scanner, external hard drive, HDMI port, USB drive or software. Users can

enter this data into a spreadsheet, database, online forms and more.

ii)Processing:This processing function is the 2nd step that offers the process and handling

of the input data instructed by the user. To process the user input data the computer needs a’

Central Processing Unit‘ (CPU).

The computer CPU, of course, is primarily obliged to process the entire process data of the

computer. The CPU takes data and instructions from the input devices and performs all

types of calculations based on the instructions given.It consists of manipulating the data in

different ways, performing calculations, modifying the instructions, coding, and executing

the actions. All this process is done on the motherboard with the help of the processor,

power supply unit and RAM presented in the CPU.

iii)Storing Data:The computer must store the data permanently so that it is available while

processing data temporarily. The function of data storage is an important component for the

proper functioning of computer systems.Basically, there are two types of storage in the CPU

of a Computer - One is RAM (used for processing the input data temporarily ) and the

second is ROM (used to store processed data permanently).

The computer must need both RAM and ROM for functioning the entire computer system

present in the CPU. RAM has low memory temporarily while ROM has a large storage

capacity for storing all the large data, information, video, images, documents, and software

in the computer permanently.

iv)Output Function:The fourth and last function of the computer is the output that means

the results generated by the computer once the processing of CPU is completed, based on

the instruction given by the user.The output is in the form of documents, videos, audio,

graphs, images, etc. that you see from the output devices such as computer monitor, printer,

speakers, headphones, screen projector, etc.

Q5: What are the components of a computer system?

Ans:

(Figure 1.1: Block diagram of a computer system)

A computer system consists of four major components. And they are: central processing

unit, input/output devices and Memory as shown in figure above:

i)Input Device: Input is any data or instruction that a computer collects from the

outside world. The input can be in the form of text, programs, commands, and user

responses.

The device that collects the input and sends it to the computer is called an input device.

Input devices include the keyboard, mouse, scanners, digital cameras, microphone, etc.

ii)CPU:The central processing unit(CPU) is the main information processor in a digital

computer capable of executing a program. The manipulation of the raw data based on

the instruction is called processing. A computer processes data in a device called the

central processing unit. It is a very complex integrated circuit, containing millions of

miniaturized electronic components.

The CPU serves as a ‘brain' of the computer. The speed of the CPU is measured in

Hertz(MHz, GHz, etc). The various types of CPU chips are intel Celeron, intel core i3,

i5, i7, etc.

Major components of CPU are Arithmetic Logic Unit(ALU),Registers,Control

Unit(CU) and Instruction Execution Unit.

iii)Storage/Memory: A computer has a huge data storage capacity. Storage is the place

where data is held in an electromagnetic or optical form for access by a computer

processor.Storage has been divided into:

a)Primary Storage:Primary storage holds data in memory. The primary storage (also

known as main memory, internal memory, or prime memory), also known as memory, is

the only one that is directly accessible to the CPU. e.g. Random Access Memory or

RAM

b)Secondary Storage:Secondary storage holds data on hard disks, tapes, and other

devices requiring input-output operations. Secondary storage (also known as external

memory or auxiliary storage) differs from primary storage where it is inaccessible to the

CPU directly.

iv)Output device:The output device is any peripheral device that receives or displays

output from a computer. Output is any computer-generated information displayed

on-screen or printed on paper. It can be in the form of words, numbers, graphics, sound,

videos, and animations.

Q6: What are Registers? What are the types of Registers?

Ans: Registers are a type of computer memory used to quickly accept, store, and

transfer data and instructions that are being used immediately by the CPU. The registers

used by the CPU are often termed as Processor registers.

A processor register may hold an instruction, a storage address, or any data .

Types of Registers:

● Accumulator: This is the most common register, used to store data taken out

from the memory.

● General Purpose Registers: This is used to store data intermediate results during

program execution. It can be accessed via assembly programming.

● Special Purpose Registers: Users do not access these registers. These registers

are for Computer system,

○ MAR: Memory Address Register are those registers that hold the address for

the memory unit.

○ MBR: Memory Buffer Register stores instruction and data received from the

memory and sent from the memory.

○ PC: Program Counter points to the next instruction to be executed.

○ IR: Instruction Register holds the instruction to be executed

(Figure 1.2: CPU registers)

Q7: Define i)Gates , ii)Memory cell.

Ans: i)Gates:Logic gates are the basic building blocks of any digital system. It is an

electronic circuit having one or more than one input and only one output. The

relationship between the input and the output is based on a certain logic. Based on this,

logic gates are named as AND gate, OR gate, NOT gate etc.

ii)Memory cell:The memory cell is the fundamental building block of computer

memory. The memory cell is an electronic circuit that stores one bit of binary

information and it must be set to store a logic 1 (high voltage level) and reset to store a

logic 0 (low voltage level).

(Figure 1.3: Memory cell operation a)Write,b)Read)

Q8: What is Interrupt?

Ans: Interrupt is a signal emitted by hardware or software when a process or an event

needs immediate attention. It alerts the processor to a high-priority process requiring

interruption of the current working process. In I/O devices one of the bus control lines is

dedicated for this purpose and is called the Interrupt Service Routine (ISR).

Q9: What do you mean by interconnection structure?

Ans: The processors must be able to share a set of main memory modules & I/O devices

in a multiprocessor system. This sharing capability can be provided through

interconnection structures. The interconnection structure that is commonly used can be

given as follows - Time-shared / Common Bus.

Q10: Discuss the bus structure.

Ans:

(Figure 1.4: Bus interconnection)

Each line is assigned a particular meaning or function.

The lines can be classified into 3 functional groups

1. Data line

2.Address line

3.Control line

1. Data line:

● Provide a path for moving data between system modules.

● These lines, collectively, are called the data bus

● Data bus may consist of from 32 to 100 separated line

● Each line can carry only one bit at a time

● Number of line in the bus determine the data rate and overall the system performance

2. Address line:

● Used to designate the source or destination of the data on the data bus

● The width of the address bus determines the maximum possible memory capacity of

the system.

3. Control line:

● Used to control the access to and the use of the data and address lines

● Since the data and the address line shared by all the components, there must be a

means of controlling their use

● Control signal transmit both commands and timing information between the modules

● Typical control lines include

1. Memory write

2. Memory read

3. I/O write

4. I/O read

5. Clock

6. Reset

7. Bus request

8. Bus grant

9. Interrupt request

10. Interrupt ACK

11. Transfer ACK

Q11: Discuss the computer memory system.

Ans: The computer memory is one of the most important elements in a computer system. It

stores data and instructions required during the processing of data and output results.

Storage may be required for a limited period of time, instantly or for an extended period of

time. Computer memory refers to the electronic holding place for instructions and data

where the processor can read quickly.

Memory Hierarchy:The memory is characterised on the basis of two key factors; capacity

and access time. The lesser the access time, the faster is the speed of memory.

The computer uses a hierarchy of memory that is organised in a manner to enable the fastest

speed and largest capacity of memory as shown in figure.

Types of Memory:

In general, memory is classified into two categories.

1. Primary memory or Main memory.

2. Secondary memory or Auxiliary memory.

1.Primary memory or main memory:The memory unit that communicates directly with

the CPU is called main memory. The primary memory allows the computer to store data for

immediate manipulation and to keep track of what is currently being processed. It is volatile

in nature, it means that when the power is turned off, the contents of the primary memory

are lost forever.

Primary memory is further classified in two categories.

1. Random Access Memory (RAM):

It is also known as read/write memory, that allows the CPU to read as well as write data and

instructions into it.

RAM is used for the temporary storage of input data, output data and intermediate results.

RAM is a microchip implemented using semiconductors.

There are two categories of RAM

(i)Dynamic RAM (DRAM) :It is made up of memory cells where each cell is composed of

one capacitor and one transistor. DRAM must be refreshed continually to store information.

The refresh operation occurs automatically thousands of times per second DRAM is slower,

less-expensive and occupies less space on the computer’s motherboard.

(ii) Static RAM (SRAM):It retains the data as long as power is provided to the memory

chip. It needs not be ‘refreshed’ periodically. SRAM uses multiple transistors for each

memory cell. It does not use a capacitor. SRAM is often used as cache memory due to its

high speed. SRAM is more expensive than DRAM.

Extended Data Output Dynamic RAM (EDO DRAM): It is a type of RAM chip. It is

used to improve the time to read content from memory and enhance the method of access.

Cache Memory:Cache memory is a storage buffer that stores the data that is used more

often. temporarily and makes them available to CPU at a fast rate.

The data and instructions that are required during the processing of data are brought from

the secondary storage devices and stored in the RAM. For processing it is required that the

data and instructions are accessed from the RAM and stored in the registers.

Cache memory is a very high speed memory placed in between RAM and CPU. Cache

memory increases the speed of processing.

Cache memory is very expensive, so it is smaller in size. Generally. Computers have cache

memory of sizes 256 KB to 2 MB.

2. Read Only Memory (ROM):

It is also known as non-volatile memory or permanent storage. It does not lose its content

when the power is switched off.ROM has only read capability, no write capability. ROM

can have data and instructions written to it only one time. Once a ROM chip is programmed

at the time of manufacturing, it cannot be reprogrammed or rewritten.

There are three categories of ROM.

(i) Programmable ROM (PROM): It is also non-volatile in nature. Once a PROM has

been programmed, its contents can never be changed. It is a one-time programmable device.

PROMs are manufactured blank and can be programmed at buffer, Final test or in system.

These types of memories are found in video game consoles, mobile phones, implantable

medical devices and high definition multimedia interfaces. PROM was invented by Wen

Tsing Chow in 1956.

(ii) Erasable Programmable ROM (EPROM): It is similar to PROM, but it can be erased

by exposure to strong ultraviolet light,then rewritten. So,it is also known as Ultraviolet

Erasable Programmable ROM (UV EPROM).EPROM was invented by Dov Frohman of

Intel in 1971.

(iii) Electrically Erasable Programmable ROM (EEPROM):It is similar to EPROM, but

it can be erased electrically, then rewritten electrically and the burning process is reversible

by exposure to electric pulses.

2.Secondary Memory (Auxiliary Memory/Storage Devices):The secondary memory

stores much larger amounts of data and information for extended periods of time. Data in

secondary memory cannot be processed directly by the CPU, it must first be copied into

primary storage i.e, RAM.Secondary storage is used to store data and programs when they

are not being processed. It is also non-volatile in nature. Due to this, the data remains in the

secondary storage as long as it is not overwritten or deleted by the user. It is a permanent

storage device i.e., device.

Secondary memory devices include.

i)Magnetic Disks :

● Hard Disk Drive.

● Floppy Disk.

● Memory Stick.

ii)Optical Disk:

● CD

● DVD

● Blue-ray Disk

iii)Solid State Disks:

● Pen/Flash Drive

Q12: What are the key characteristics of a computer memory system?

Ans: The key characteristics of memory devices or memory system are as follows:

1. Location

2. Capacity

3. Unit of Transfer

4. Access Method

5. Performance

6. Physical type

7. Physical characteristics

8. Organization

1. Location:

It deals with the location of the memory device in the computer system. There are three

possible locations:

● CPU : This is often in the form of CPU registers and small amount of cache

● Internal or main: This is the main memory like RAM or ROM. The CPU can

directly access the main memory.

● External or secondary: It comprises secondary storage devices like hard disks,

magnetic tapes. The CPU doesn’t access these devices directly. It uses device

controllers to access secondary storage devices.

2. Capacity:

The capacity of any memory device is expressed in terms of: i)word size ii)Number of

words

i)Word size: Words are expressed in bytes (8 bits). A word can however mean any

number of bytes. Commonly used word sizes are 1 byte (8 bits), 2bytes (16 bits) and 4

bytes (32 bits).

ii)Number of words: This specifies the number of words available in the particular

memory device. For example, if a memory device is given as 4K x 16.This means the

device has a word size of 16 bits and a total of 4096(4K) words in memory.

3. Unit of Transfer:

It is the maximum number of bits that can be read or written into the memory at a time.

In case of main memory, it is mostly equal to word size. In case of external memory, the

unit of transfer is not limited to the word size; it is often larger and is referred to as

blocks.

4. Access Methods:

It is a fundamental characteristic of memory devices. It is the sequence or order in

which memory can be accessed. There are three types of access methods:

● Random Access: If storage locations in a particular memory device can be

accessed in any order and access time is independent of the memory location

being accessed. Such memory devices are said to have a random access

mechanism. RAM (Random Access Memory) ICs use this access method.

● Serial Access: If memory locations can be accessed only in a certain

predetermined sequence, this access method is called serial access. Magnetic

Tapes, CD-ROMs employ serial access methods.

● Semi random Access: Memory devices such as Magnetic Hard disks use this

access method. Here each track has a read/write head thus each track can be

accessed randomly but access within each track is restricted to a serial access.

5. Performance: The performance of the memory system is determined using three

parameters

● Access Time: In random access memories, it is the time taken by memory to

complete the read/write operation from the instant that an address is sent to the

memory. For non-random access memories, it is the time taken to position the

read write head at the desired location. Access time is widely used to measure

performance of memory devices.

● Memory cycle time: It is defined only for Random Access Memories and is the

sum of the access time and the additional time required before the second access

can commence.

● Transfer rate: It is defined as the rate at which data can be transferred into or out

of a memory unit.

6. Physical type: Memory devices can be either semiconductor memory (like RAM) or

magnetic surface memory (like Hard disks).

7.Physical Characteristics:

● Volatile/Non- Volatile: If a memory device continues to hold data even if power

is turned off. The memory device is non-volatile else it is volatile.

8. Organization:

● Erasable/Non-erasable: The memories in which data once programmed cannot

be erased are called Non-erasable memories. Memory devices in which data in the

memory can be erased is called erasable memory.

E.g. RAM(erasable), ROM(non-erasable).

Q13: What is cache memory?

Ans: Cache memory, also called cache, supplementary memory system that temporarily

stores frequently used instructions and data for quicker processing by the central processing

unit (CPU) of a computer.

Q14: What is Disk Cache?

Ans: A disk cache is a mechanism for improving the time it takes to read from or write to a

hard disk. Today, the disk cache is usually included as part of the hard disk. A disk cache

can also be a specified portion of random access memory (RAM). The disk cache holds data

that has recently been read and, in some cases, adjacent data areas that are likely to be

accessed next. Write caching is also provided with some disk caches.

Q15: What are the techniques of I/O operations?

Ans:There are three technique for I/O operation , which are:

● Programmed I/O

● Interrupt driven I/O

Direct Memory Access

● Programmed I/O :With programmed I/O, data are exchanged between the processor

and the I/O module. The processor executes a program that gives it direct control of

the I/O operation, including sensing device status, sending a read or write command,

and transferring the data. When the processor issues a command to the I/O module, it

must wait until the I/O operation is complete.

● Interrupt driven I/O :With interrupt-driven I/O, the processor issues an I/O command,

continues to execute other instructions, and is interrupted by the I/O module when the

latter has completed its work.

● Direct Memory Access :With direct memory access (DMA), the I/O module and

main memory exchange data directly without processor involvement.

Q16: What are the differences between RAM and ROM?

Ans:

Q17: What is the external I/O interface?

Ans: External interfaces are typically a product's lifeline to the outside world. Such

interfaces may be used for a number of purposes, including connecting to peripherals, field

programming, or testing during product manufacturing. Typical interfaces include FireWire,

USB , RS232, Ethernet, or JTAG IEEE 1149.1 ,InfiniBand.

Q18:Discuss the functions of the I/O module.

Ans: Functions of the I/O module:

● Processor communication - This involves a number of tasks, primarily the

transference of data between the processor and an I/O module, accepting and

decoding commands sent by the processor, reporting of current status, and an ability

for the I/O module to recognise its own unique address.

● Device communication - It needs to be able to perform standard device

communications, such as reporting of status.

● Control and timing - An I/O module needs to be capable of managing data flow

between a computer’s internal resources and any connected external devices.

● Data buffering - A crucial function that manages the speed discrepancy that exists

between the speed of transfer of data between the processor and memory and

peripheral devices.

● Error detection - Detecting errors, whether mechanical (such as a printer

experiencing a paper jam) or data based, and reporting them to the processor is

another vital function of an I/O module.

Q19: What are the categories of external devices? Draw the external

device block diagram.

Ans :

We can broadly classify external devices into three categories:

1) Human readable: Suitable for communicating with the computer user. Ex: Video

Display Terminals (VDTs), printers.

2) Machine readable: Suitable for communicating with equipment. Ex: magnetic disk

and tape systems, and sensors and actuators, such as are used in a robotics application.

3) Communication: Suitable for communicating with remote devices. Communication

devices allow a computer to exchange data with a remote device, which may be a

human-readable device, such as a terminal, a machine-readable device, or even another

computer.

(Figure 1.6: Block diagram of an external device)

The interface to the I/O module is in the form of control, data, and status signals.

Control signals determine the function that the device will perform, such as send data to

the I/O module (INPUT or READ), accept data from the I/O module (OUTPUT or

WRITE), report status, or perform some control function particular to the device (e.g.,

position a disk head). Data is in the form of a set of bits to be sent to or received from

the I/O module. Status signals indicate the state of the device. Examples are

READY/NOT-READY to show whether the device is ready for data transfer.

Control logic associated with the device controls the device’s operation in response to

direction from the I/O module. The transducer converts data from electrical to other

forms of energy during output and from other forms to electrical during input. Typically,

a buffer is associated with the transducer to temporarily hold data being transferred

between the I/O module and the external environment; a buffer size of 8 to 16 bits is

common.

Q20: Discuss the I/O module structure.

Ans:

(Figure 1.7: Block diagram of I/O module structure)

● The module connects to the rest of the computer through a set of system bus lines.

Data transferred to and from the module are buffered in one or more data registers.

One or more status registers provide current status information. A status register may

also function as a control register, to accept detailed control information from the

processor. The logic within the module interacts with the processor via a set of

control lines. The processor uses the control lines to issue commands to the I/O

module.

-Some of the control lines may be used by the I/O module for status signals. Each I/O

module has a unique address or a unique set of addresses if it controls more than one

external device.

● An I/O module may hide the details of timing, formats, and the electro mechanics of

an external device so that the processor can function in terms of simple read and write

commands, and possibly open and close file commands. In its simplest form, the i/o

module may still leave much of the work of controlling a device (e.g., rewind a tape)

visible to the processor.

● An I/O module that takes on most of the detailed processing burden, presenting a

high-level interface to the processor, is usually referred to as an I/O channel or I/O

processor. An I/O module that is quite primitive and requires detailed control is

usually referred to as an I/O controller or device controller. I/O controllers are

commonly seen on microcomputers, whereas I/O channels are used on mainframes.

Q21: What is a Hard Disk Drive(HDD)?

Ans: A hard disk drive (HDD) is a non-volatile computer storage device containing

magnetic disks or platters rotating at high speeds. It is a secondary storage device used

to store data permanently, random access memory (RAM) being the primary memory

device. Non-volatile means data is retained when the computer is turned off.

A hard disk drive is also known as a hard drive.

Q22: What is Motherboard?

Ans:A motherboard (also called mainboard, main circuit board,or mobo) is the main printed

circuit board (PCB) in general-purpose computers and other expandable systems. It holds

and allows communication between many of the crucial electronic components of a system,

such as the central processing unit (CPU) and memory, and provides connectors for other

peripherals . Unlike a backplane, a motherboard usually contains significant sub-systems,

such as the central processor, the chipset's input/output and memory controllers, interface

connectors, and other components integrated for general use.

Motherboard means specifically a PCB with expansion capabilities. As the name suggests,

this board is often referred to as the "mother" of all components attached to it, which often

include peripherals, interface cards, and daughterboards: sound cards, video cards, network

cards , host bus adapters, TV tuner cards, IEEE 1394 cards; and a variety of other custom

components.

Similarly, the term mainboard describes a device with a single board and no additional

expansions or capability, such as controlling boards in laser printers, television sets,

washing machines, mobile phones, and other embedded systems with limited expansion

abilities.

Operating System Sample [Notes]

This Course is Only Available On Our App

CDAC CCAT Study Materials

The one-stop destination for everything you need for CDAC CCAT Exam Preparations

Curriculum

This Course is Only Available On Our App

CDAC CCAT Study Materials

The one-stop destination for everything you need for CDAC CCAT Exam Preparations

Operating System Sample [Notes]

Login with your site account

Register a new account

Modal title