Student Lecture Note

8/19/2019 Student Lecture Note

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Operating Systems/Windows Application

SALAKO, E. A (2014) Page 1

Process Po

Process P1

1

2

Swap out

Swap in

Operating System

User space

Main memory Backing store

Memory management (swapping mechanism)


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COURSE CODE: CSC 222

COURSE UNIT: 2

LEVEL: 200

PROGRAMEE: NCE

COURSE CONTENTS

Definition and functions of Operating system (OS)

Advantages and disadvantages of using (OS)

Windows (types, uses, etc)

Assemblers, Compilers and Interpreters

Batch processing, Real time processing and time sharing processing

Resource Allocation

Memory management

Input/output systems


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INTRODUCTION

DEFINITION AND FUNCTIONS OF OPERATING SYSTEM (OS)

ccording Salako (2011), a computer is a programmable machine designed to

sequentially accept, process, store data on the basis of set of predefined instructions

to produce useful information. A computer cannot work or perform functions outside a

predefined set of instructions. The physical appearance of a computer does not guarantee

high performance. What makes computer different and useful in solving many humanly

problems is the platform that drives its functionalities. This platform controls the

functionalities of a computer. The performance of a computer is strictly depends on the

two criteria; namely the capability of hardware and the efficiency of software. This course

note (material) reviews one of the essential components of a computer system (system

software); the Operating System (OS). The note also focuses on the functions of Operating

System (OS); advantages and disadvantages of using (OS); Windows (types, uses, etc);

assemblers, translators and interpreters; batch processing, real time processing and time

sharing processing; allocation and scheduling resource; memory management and

input/output systems.

Read the note with your mind

What is system software?

Let start the discussion by asking ourselves this fundamental question “what is

system software? System software is a set of one or more programs, designed to control

A


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the operation of a computer system. These programs do not solve specific problems like

custom made application software. They are general programs written by computer

programmers to assist human in the use of the computer system by performing tasks, such

as controlling all of the operations, required to move data onto and out of a computer and

all the steps in executing an application program. In general, system software (packages)

support the running of other software; communicate with peripheral devices (keyboard,

mouse, CRT, printer, disk and tape devices, etc.); support the development of other types

of software; and monitor the use of various hardware resources (memory, peripherals,

CPU, etc.). Thus systems software makes the operation of the computer system more

effective and efficient. The program included in systems software are called systems

programs and the person who prepares systems software is referred as to as system

programmer.

Categories of System Software

The system software is an essential part of a total computer system. Its function is to

compensate for the differences that exist between the use and the capabilities of the

hardware. A computer without some kind of systems software would be very ineffective

and most likely impossible to operate. The basic categories of system software include:

a. Operating System (OS)

b. Device Driver

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c. Utility Programs

(a) Operating system

An operating system (OS) is a collection of software that manages computer

hardware resources and provides common services for computer programs. The operating

system is an essential component of the system software in a computer system. Application

programs usually require an operating system to function. Time-sharing operating systems,

schedule tasks for efficient use of the system and may also include accounting for cost

allocation of processor time, mass storage, printing, and other resources.

For hardware functions such as input, output and memory allocation, the operating system

acts as an intermediary between programs and the computer hardware, although the

application code is usually executed directly by the hardware and will frequently make

a system call to an OS function or be interrupted by it. Operating systems can be found on

almost any device that contains a computer — from cellular phones and video game

consoles to super-computer and web servers. Examples of popular modern operating

systems include Android, Microsoft Windows, Windows Phone, IBM z/OS and LINUS to

mention but a few.

Major components of operating system (OS)

Most Operating Systems (OS ) have many similar elements. These generally include:

Supervisor

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Command language translator

I/O control system (IOCS)

Librarian

Supervisor

At the heart of every OS is a program called supervisor. The overall coordination and

the management of OS are performed by this program. Located in primary memory when

the computer system is on, the supervisor initiates the call to other parts of the OS

for resources and places any programs that are retrieved during the process into main

memory.

Command Language Translator

The command language translator transforms the needs of users onto actions that the

OS takes. Like other software packages, the OS has its own language with which users and

programmers issue commands. Command language translator converts the English like

commands of OS (DIR, COPY, CLS, or DEL) into the machine language of the computer.

I/O Control System (IOCS)

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This input/output control system (IOCS) interacts with input and output hardware devices.

Thus, if the supervisor determines that a program should be retrieved from hard disk to

main memory for a user, it hands the task over to the IOCS. Supervisor actually supervise

the input and output devices, the actual work is basically done by IOCS.

Librarian

Computer hard disk is basically a library. The librarian is the software element that catalogs

and manages data, file, directories, programs, space, and users.

Types of operating systems

1. Real-time

A real-time operating system is a multitasking operating system that aims at executing real-

time applications. Real-time operating systems often use specialized scheduling algorithms

so that they can achieve a deterministic nature of behavior. The main objective of real-time

operating systems is their quick and predictable response to events. They have an event-

driven or time-sharing design and often aspects of both. An event-driven system switches

between tasks based on their priorities or external events while time-sharing operating

systems switch tasks based on clock interrupts.

2.

Multi-user

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A multi-user operating system allows multiple users to access a computer system at the

same time. Time-sharing systems and Internet servers can be classified as multi-user

systems as they enable multiple-user access to a computer through the sharing of time.

Single-user operating systems have only one user but may allow multiple programs to run

at the same time.

3. Single-tasking

This is one of the operating systems that control the functionalities of a computer system.

A single-tasking system has only one program running at a time. Multiple programs cannot

run simultaneously; one running program at a time. This operating system is designed to

manage the computer so that one user can effectively perform a task at a time. The Palm

OS for palm handheld computers is a good example of a modern single-user, single-task

operating system. Single-tasking results in completing a task faster than performing more

than a task.

4. Multi-tasking

A multi-tasking operating system allows more than one program to be running at the same

time, from the point of view of human time scales. Multi-tasking can be of two types: pre-

emptive and co-operative. In pre-emptive multitasking, the operating system slices the

CPU time and dedicates one slot to each of the programs. Unix-like operating systems such

as Solaris and Linux support pre-emptive multitasking, as does Amiga OS. Cooperative

multitasking is achieved by relying on each process to give time to the other processes in

a defined manner. The 16-bit versions of Microsoft Windows used cooperative multi-

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tasking. The 32-bit versions of both Windows NT and Win9x, used pre-emptive multi-

tasking. Mac OS prior to OS X used to support cooperative multitasking.

Is it better to focus on one task at a time, ormaximize your time by performing many taskssimultaneously? Discuss

uestion

5. Distributed

A distributed operating system manages a group of independent computers and

makes them appear to be a single computer. The development of networked computers that

could be linked and communicate with each other gave rise to distributed computing.

Distributed computations are carried out on more than one machine. When computers in a

group work in cooperation, they make a distributed system.

6. Embedded

Embedded operating systems are designed to be used in embedded computer

systems. They are designed to operate on small machines like PDAs with less autonomy

(independence). They are able to operate with a limited number of resources. They are very

compact and extremely efficient by design. Windows CE and Minix 3 are some examples

of embedded operating systems.

Advantages of computer operating system (OS)

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The advantages of computer operating system (OS) include:

i. make computers easy to use

ii. user friendly

iii.

it serves as an intermediate between all hardwares and softwares of the system

iv.

no need to know any technical or programming languages

v. it is the platform of all computer programs to run

Disadvantages of computer operating system (OS)

The disadvantages of computer operating system (OS) include:

i.

if any problems affect OS, you may lose all the contents which have been stored

already

ii. unwanted users can use your own system

iii. prone to virus infections

iv.

few experts can develop the programs; so it requires deep knowledge and

certification.

Functions of operating system(s)

The functions of operating system(s) include the following:

i.

helps in booting up process of the computer


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ii.

checking that the hardware is functioning properly

iii. scheduling and loading of jobs in order to provide continuous processing

iv.

control of user selection and operation of I/O devices and file handling

v.

calling into main storage of programs and subroutines, as and when required

vi. opening and closing files, checking of files labels etc.

vii.. maintenance of directories in external storages

viii.

provision of error corrections routines

ix.

communications with the computer user by means of Input and output devices

x.

managing tasks such as multitasking, multiprogramming, multiprocessing, and

timesharing.

b. Device Drivers

This software extends the capabilities of OS support I/O devices. Computer does

not have Intelligence Quotient (IQ). It is the device driver that tells the computer that

monochrome monitor is replaced with color monitor, sound card is attached to the CPU,

fax modem card is linked with the computer etc. These device drivers are programs.

c. Utility Software

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Utility software is a computer software designed to help in the enhancement of

operating system, computer hardware and application software. It is designed to perform

specific single-task or a multiple of small tasks. Examples of utility software include:

i.

Disk defragmenters

ii. system profilers

iii. network managers

iv. application launchers

v.

virus scanners.

Utility software designed to help analyse, configure, optimize or maintain a computer for

the realization of predefined goals.

ADVANTAGES AND DISADVANTAGES OF DIFFERENT (OSs)

As mentioned above, there are many different versions of operating systems, the

advantages and disadvantages of a few of them are discussed below.

1. Advantages of Windows

The advantages of windows include:

i. Window enhances entertainment. Lots of software and games are developed for

windows.

ii.

Windows is user friendly.

Disadvantages of Windows


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The disadvantages of windows include:

i. Very bloated with many features most people don't use, thus slowing down the

computer and takes excessive hard drive space. However this shouldn't be much of

a problem with newer computers.

ii. There are many viruses programmed for windows

iii.

Can get a little expensive

2.

Advantages of MAC OS X

The advantages of MAC OS X include:

i. Very user friendly with nice graphics

ii.

very few viruses are programmed for OS X

iii.

Some selection of software and games.

Disadvantages of MAC OS X

The disadvantages of MAC OS X include:

i. The computers are overpriced; also can get expensive for software

3. Advantages of LINUX

The advantages of LINUX include:

i.

has many versions that are designed to do specific tasks

ii.

programmer friendly

iii. there are many versions that have what you need and will not slow down your

computer

iv.

few viruses infections


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v.

advanced users can COMPLETELY customize the system

Disadvantages of LINUX

The disadvantages of LINUX include:

i.

not very user friendly

ii.

few software selections

TYPES AND USES OF WINDOWS

The Window supports limited forms of multitasking and networking but shares the memory

limitations of Disk Operating System (DOS). Early versions of windows had some

problems with application crashes when multiple programs competed for the same memory

space.

Microsoft's Windows 98 and Windows 95 are genuine 32-bit operating system. A 32-bit

operating system can run faster than DOS, which could only address data in 32-bit chunks.

Both Windows 98 and 95 provide a streamlined graphical user interface that arranges icons

to provided instant access to common tasks. They can support software written for DOS

but can also run programs that take up more than 640K of memory. Window 98 and 95

feature multitasking, multithreading (the ability to manage multiple independent tasks

simultaneously), and powerful networking capabilities, including the capability to integrate

fax, e-mail, and scheduling programs.

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Window 98 is faster and more integrated with the Internet than Window 95, with support

for new hardware technologies such as MMX, digital video disks (DVD),

videoconferencing cameras, scanners, TV tuner-adapter cards, and joysticks. It provides

capabilities for optimizing hardware performance and file management on the hard

disk and enhanced three-dimensional graphics. The most visible feature of Window 98 is

the integration of the operating system with web browser software.

Windows NT

Windows NT (for new technology) is another 32-bit operating system developed by

Microsoft with features that make it appropriate for applications in large networked

organizations. It is used as an operating system for high-performance workstations and

network servers. Windows NT shares the same graphical user interface as the other

Windows operating systems, but it has more powerful networking, multitasking, and

memory-management capabilities. Window NT can support existing software written for

DOS and Windows, and it can provide mainframe-like computing power for new

applications with massive memory and file requirements. It can even support

multiprocessing with multiple CPUs.

There are two versions of Windows NT; a Workstation version for user of standalone or

client desktop computers. And a Server version designed to run on network servers.

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Windows NT Server includes tools for creating and operating websites. Unlike OS/2,

Windows NT is not tied to computer hardware based on Intel microprocessors.

Windows CE

Window CE has some of the capabilities of Windows, including its graphical user interface

(GUI), but it designed to run on small handheld computers, personal digital assistants, or

wireless communication devices such as pagers and cellular phones. It is a portable and

compact operating system requiring very little memory. Non-PC and consumer devices can

use this operating system to share information with Window-based PCs and connect to the

Internet.

According to Vangie (2012), Microsoft Windows is a family of operating systems for

personal computers. Windows dominates the personal computer world, running, by some

estimates, on more than 90 percent of all personal computers – the remainder

running Linux and Macoperating systems. Windows provides a graphical user

interface(GUI), virtual memory management, multitasking, and support for many

peripheral devices. The following details the history of Microsoft operating systems

designed for personal computers (PCs).

MS-DOS (Microsoft disk operating system)

Originally developed by Microsoft for IBM, MS-DOS was the standard operating system

for IBM-compatible personal computers. The initial versions of DOS were very simple and

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resembled another operating system called CP/M. Subsequent versions have become

increasingly sophisticated as they incorporated features of minicomputer operating

systems.

Windows 1.0 – 2.0 (1985-1992)

Introduced in 1985, Microsoft Windows 1.0 was named due to the computing boxes, or

"windows" that represented a fundamental aspect of the operating system. Instead of

typing MS-DOS commands, windows 1.0 allowed users to point and click to access the

windows.

Windows 3.0 – 3.1 (1990 – 1994)

Microsoft released Windows 3.0 in May, 1900 offering better icons, performance and

advanced graphics with 16 colors designed for Intel 386 processors.

Windows 95 (August 1995)

A major release of the Microsoft Windows operating system released in 1995. Windows

95 represents a significant advance over its precursor, Windows 3.1. In addition to sporting

a new user interface, Windows 95 also includes a number of important internal

improvements. Perhaps most important, it supports 32-bit applications, which means that

applications written specifically for this operating system should run much faster.

Windows 98 (June 1998)

Windows 98 offers support for a number of new technologies, including FAT32, AGP,

MMX, USB, DVD, and ACPI. Its most visible feature, though, is the Active Desktop,

which integrates the Web browser (Internet Explorer) with the operating system. From the

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user's point of view, there is no difference between accessing a document residing locally

on the user's hard disk or on a Web server halfway around the world.

Windows ME - Millennium Edition (September 2000)

The Windows Millennium Edition, called "Windows Me" was an update to the Windows

98 core and included some features of the Windows 2000 operating system. This version

also removed the "boot in DOS" option.

Windows NT 31. - 4.0 (1993-1996)

A version of the Windows operating system. Windows NT (New Technology) is a 32-bit

operating system that supports preemptive multitasking.

Windows 2000 (February 2000)

Often abbreviated as "W2K," Windows 2000 is an operating system for business desktop

and laptop systems to run software applications, connect to Internet and intranet sites, and

access files, printers, and network resources.

Windows XP (October 2001)

Windows XP was first introduced in 2001. Along with a redesigned look and feel to the

user interface, the new operating system is built on the Windows 2000 kernel, giving the

user a more stable and reliable environment than previous versions of Windows.

Windows Vista (November 2006)

Windows Vista offered an advancement in reliability, security, ease of deployment,

performance and manageability over Windows XP. New in this version was capabilities to

detect hardware problems before they occur, security features to protect against the latest

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generation of threats, faster start-up time and low power consumption of the new sleep

state.

Windows 7 (October, 2009)

Windows 7 made its official debut to the public on October 22, 2009 as the latest in the 25-

year-old line of Microsoft Windows operating systems and as the successor to Windows

Vista (which itself had followed Windows XP).

Windows 8 (October 2012)

Windows 8 is a completely redesigned operating system that's been developed from the

ground up with touchscreen use in mind as well as near-instant-on capabilities that enable

a Windows 8 PC to load and start up in a matter of seconds rather than in minutes. Windows

8 will replace the more traditional Microsoft Windows OS look and feel with a new

"Metro" design system interface that first debuted in the Windows Phone 7 mobile

operating system.

Windows 8 (August 2014)

Windows 8.1 runs on touchscreen devices as well as traditional computers that rely on a

mouse and keyboard. Microsoft designed Windows 8.1 to address widespread complaints

about Windows 8. Most notably, Windows 8.1 reinstated the Start button, a familiar

navigational feature of previous OS versions. Microsoft also made it easier to open, close

and multitask among several apps using a mouse.

Windows 10 (29 July 2015)

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Windows 10 is a multi-tasking operating system designed by Microsoft as a major aspect

of Windows OSs. Window 10 combines the strengths of Windows 8, 8.1 with Windows 7.

ASSEMBLERS, COMPILERS AND INTERPRETERS

In the world of programming, there is a term called translator. A translator is a program

which converts statements (program or instructions) written in one language to statements

in another language especially to machine language. There are three types of translators:

1. Assemblers

2. Compilers

3. Interpreters

THE ASSEMBLER: This is a program, which translate assembly language into machine

code. One machine instruction is generated for each source instruction. The resulting

program can only be executed when the assembly process is completed. The assembler

reserves space for the instructions and data, replaces mnemonic operating codes by

machine codes and symbolic addresses by numeric addresses while it determines the

machine representation of constants.

Functions of the assembler

The functions of a typical assembler include the followings:

i. It translates mnemonic operation codes and symbolic addresses into machine codes

and addresses.

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ii.

Includes the necessary linkages for closed subroutines and insert appropriate

machine codes.

iii.

Allocates area of storage.

iv.

Detects and indicates invalid source language instructions.

v.

Produces the object program on disk as required.

vi.

Produces a printed listing of the source and object program with comments.

THE COMPILER : Compiler translates a high level language into machine language. The

compiler translate the whole source program into machine code or object program prior to

the object being loaded into main memory and execution. The resulting program can only

be executed when compilation is completed. The storage of the object program into a

diskette facilities future usage of the high level language source program any other time it

is needed.

HOW THE COMPILER DOES ASSEMBLER WORK ?

The following steps guide the students on how the compilers do the assemblers’ work:

1.

Translates the source program statements into machine code.

2.

Includes linkage for closed subroutines.

3.

Allocates areas of main storage.

4.

Generates the object program on cards, tapes or disc as required.

5. Produces a printed copy of the source and object program when required.

6.

Tabulates list of errors found during program compilation e.g. the use of ‘word’ or

statement not included in the language vocabulary, the rule of syntax or lexis.


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THE INTERPRETER: Interpreter is more easily understood by comparing them with

compiler. Both compilers and interpreters are commonly used for the translation of high-

level language program but they perform the translation in two completely different ways.

In the compiler, the whole of the high level language source program is converted into

machine code object program prior to the object program being loaded into main memory

for execution. This in contrast to the interpreter which deals with the source program one

instruction at a time, completely translating and executing each instruction before it goes

onto the next. Interpreter seldom produce object codes but call upon in-built routines

instead. However, some intermediate codes are usually produced temporarily.

The interpreter does not produce object program, it read source program, translates it and

goes ahead to execute it. The object program provided by a compiler fastens execution than

any interpreter can do in the running of a program, the use of object program may however

pose a problem where there is an error as it is very time consuming to discover the source

of error, a compiler is capable of producing a machine code generated by it at any time,

whereas an interpreter can only execute the source program.

If a computer is used, the same program needs only to be translated once. Thereafter, the

object program can be loaded directly into main storage and executed. However, when an

interpreter is used, the source program will be translated every time the program is

executed. Execution carried out in this way may be ten times slower than the execution of

the equivalent object programs.

Uses of interpreters


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The uses of interpreters include the followings:

i. handling user commands in an interactive system.

ii.

they debug programs as they run (i.e. removing faults) i.e. for each line of coding

before implemented.

iii. handling software produced for or by different computer. In this case, the interpreter

may be essential if:

(a)

two dissimilar machines are to be connected together for operation, or

(b)

if software produced on an old model and not yet converted had to be run on a

new one. This procedure is referred to as SIMULATION since interpreter allow

the new computer to simulate the behavior of the old.

iv.

interpreter can also be used to simulate a new machine not yet provided but for

which software is already written.

BATCH PROCESSING, REAL TIME PROCESSING AND TIME SHARING

PROCESSING

How a computer processes data can be classified into three:

i. Batch Processing

ii.

Real Time Processing

iii.

Time Sharing Processing

i. Batch processing


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Batch processing is assembling a group of jobs or tasks in a batch. The earliest computers

were extremely expensive devices, and very slow. Machines were typically dedicated to a

particular set of tasks and operated by control panels, the operator manually entering small

programs via switches in order to load and run a series of programs. These programs might

take hours, or even weeks, to run. As computers grew in speed, run times dropped, and

soon the time taken to start up the next program became a concern. Batch

processing methodologies evolved to decrease these "dead periods" by queuing up

programs so that as soon as one program completed, the next would start.

To support a batch processing operation, a number of comparatively inexpensive card

punch or paper tape writers were used by programmers to write their programs "offline".

When typing (or punching) was complete, the programs were submitted to the operations

team, which scheduled them to be run. Important programs were started quickly; how long

before less-important programs were started was unpredictable. When the program run was

finally completed, the output (generally printed) was returned to the programmer. The

complete process might take days, during which time the programmer might never see the

computer.

The alternative of allowing the user to operate the computer directly was generally far too

expensive to consider. This was because users might have long periods of entering code

while the computer remained idle. This situation limited interactive development to those

organizations that could afford to waste computing cycles. Programmers at the Universities

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decried the in-humanist behaviors that batch processing imposed, to the point that Stanford

students made a short film humorously critiquing it. They experimented with new ways to

interact directly with the computer, a field today known as human-computer interaction.

ii. Real time processing

Data processing actually takes place instantaneously upon data entry or receipt of a

command or instruction.

Real time processing is a type of processing where something is maintained or created live,

and not after or before the event has happened. This is used frequently in electronics. A

disadvantage of real time processing may be errors that were not foreseen due to not

waiting or preparing before or after. Real-time processing is just that, processing

calculations right now, in real time. Something like crediting payments to a person's

monthly bill would be an example of real time processing. The payments are processed as

they come in, on a first come, first served basis.

iii. Time-sharing

Time-sharing, in data processing, is the method of operation in which multiple users with

different programs interact nearly simultaneously with the central processing unit of a

large-scale digital computer. Because the central processor operates substantially faster

than does most peripheral equipment (e.g.,video display terminals, tape drives, and

printers), it has sufficient time to solve several discrete problems during the input/output

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process. Even though the central processor addresses the problem of each user in sequence,

access to and retrieval from the time-sharing system seems instantaneous from the

standpoint of remote terminals since the solutions are available to them the moment the

problem is completely entered.

Time-sharing was developed during the late 1950s and early ’60s to make more efficient

use of expensive processor time. Commonly used time-sharing techniques

include multiprocessing, parallel operation, and multiprogramming.

Also, many computer networks organized for the purpose of exchanging data and

resources are centered on time-sharing systems.

Time sharing is also called time slicing. The CPU divides the number of clock cycles it has

per second among several processes. Think a multilane freeway and cars all merging to

cross a river on a 1 lane bridge. Distributed processing means more than one CPU working

in parallel. In the freeway analogy, think 1 lane from the freeway splitting and using more

than one bridge across the river. The load is distributed over two or more bridges. All of

these are just various ways and means of accomplishing one or more tasks from a group of

one or more tasks.

RESOURCE ALLOCATION

To begin the resource allocation, there are fundamental terms that needed to be understood

by the leaners. These terms are resource(s) and process(es).


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What is resource?

A resource also called system resource, is any physical or virtual component within a

computer system. Every device connected to a computer system is a resource. Every

internal system component is a resource. For examples, keyboard, mouse, RAM, hard

disks, video cards, network cards etc are usable parts of a computer that can be controlled

and assigned by the operating system so all of the hardware and software on the computer

can work together as designed.

What is process?

A process is an instance of a program running in a computer. It is close in meaning to task,

a term used in some operating systems. A process is an instance of a computer program

that is being executed. It contains the program code and its current activity.

Resource allocation

Resource allocation is necessary for any application to run on the system. When the user

opens (clicks) any program this will be counted as a process, and therefore requires

the computer to allocate certain resources for it to be able to run. Resource allocation

involves balancing competing needs and priorities and determining the most effective

course of action (processing) in order to maximize the effective use of limited resources

and gain the best return (output). According to Chris (n.d), general issues on resource

allocation include:


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In a multi-processing environment, usually processes request more resources than

there are available.

It would be too expensive to provide enough non-shareable resources to cope with

maximum demand.

OS must ensure that processes get the resources they request without compromising

system integrity.

E.g., non-shareable resources cannot be shared amongst processes, because

otherwise input or output could be meaningless (Printer intermingling output from

several processes).

Allocating Resources

In allocating resources, deadlock should be handled sensibly, high level of resource

utilisation should be guaranteed, processes should be allocated resources within a

reasonable length of time and the last two points compromise each other. However,

operating system (OS) can ensure high level of resource utilisation, but sometimes

compromising response times for process completion.

Allocation Mechanisms

A resource is a component of the computer system for which processes can compete.

Typically these are:

i.

Central Processors


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Usually one, but in a multi-processor environment there will be more than one

processors.

Processors may be several of the same type, or some may have specific

characteristics, to be dedicated to certain tasks.

OS needs to know what each processor can do to help it allocate processor to a

process - uses Processor Descriptor.

Each processor may have its own processor queue, to queue jobs.

ii. Memory

Processes and data need to be in primary memory to be operated on.

Memory is finite, and Memory Manager must create enough space in primary

memory to accommodate a process for it to become runnable.

iii. Peripherals

Each device has a device descriptor

Input Output Request Blocks (IORBs) are added to device request queue.

Mutual exclusion to non-shareable peripherals is managed by setting semaphore's

initial value to 1.

iv. Backing Store

Can be used for Virtual Memory - managed by memory manager

Can also be used for File Store - managed by filing system.


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Requests for space granted, unless there is no space left, or user has exceeded quota.

Requests cannot be queued.

v. Files

Collections of related information (Programs, Data, Etc.)

Access may be restricted - security

Access may be limited - non-shareable in write mode

Access may be unlimited - shareable in read mode

Requests may be queued until the expiration of some timeout.

Deadlock

A deadlock occurs when Process A holds non-shareable resource X and requests non-

shareable resource Y, and Process B holds resource Y and requests resource X.

Example of a Resource Allocation Graph

Four necessary and sufficient conditions for deadlock include:


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i.

Mutual Exclusion - non-shareable resources

ii.

Hold and Wait

iii.

No Pre-emption

iv.

Circular Waiting

Deadlock can be resolved by the followings:

i.

Preventing any one of the conditions from holding

ii.

Detection and recovery

iii.

Avoidance by anticipation

MEMORY MANAGEMENT

Memory management is the functionality of an operating system which handles or manages

primary memory of a computer. Memory management keeps track of each and every

memory location either it is allocated to some processes or it is free. It checks how much

memory is to be allocated to processes. It decides which process will get memory at what

time. It tracks whenever some memory gets freed or unallocated and correspondingly it

updates the status.

Memory management provides protection by using two registers, a base register and a

l imit register . The base register holds the smallest legal physical memory address and the

limit register specifies the size of the range. For example, if the base register holds 300,000


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and the limit register is 120,000, then the program can legally access all addresses from

300,000 through 411,999.

Operating System

(OS)

Process 1

Process 2

Process 3

Process 4

300,000

120,000

Base

Limit

Empty Space

0

251000

300000

420000

650000

820000

1920000

Instructions and data to memory addresses can be done in following ways:

Compile time -- When it is known at compile time where the process will reside, compile

time binding is used to generate the absolute code.

Load time -- When it is not known at compile time where the process will reside in

memory, then the compiler generates re-locatable code.

Execution time -- If the process can be moved during its execution from one memory

segment to another, then binding must be delayed to be done at run time


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Dynamic Loading

In dynamic loading, a routine of a program is not loaded until it is called by the program.

All routines are kept on disk in a re-locatable load format. The main program is loaded into

memory and is executed. Other routines methods or modules are loaded on request.

Dynamic loading makes better memory space utilization and unused routines are never

loaded.

Dynamic Linking

Linking is the process of collecting and combining various modules of code and data into

an executable file that can be loaded into memory and executed. Operating system can link

system level libraries to a program. When it combines the libraries at load time, the linking

is called static linking and when this linking is done at the time of execution, it is called

as dynamic linking. In static linking, libraries linked at compile time, so program code

size becomes bigger whereas in dynamic linking libraries linked at execution time so

program code size remains smaller.

Logical versus physical address space

An address generated by the CPU is a logical address whereas address actually available

on memory unit is a physical address. Logical address is also known a Virtual address.

Virtual and physical addresses are the same in compile-time and load-time address-binding

schemes. Virtual and physical addresses differ in execution-time address-binding scheme.


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The set of all logical addresses generated by a program is referred to as a logical address

space. The set of all physical addresses corresponding to these logical addresses is referred

to as a physical address space.

The run-time mapping from virtual to physical address is done by the memory management

unit (MMU) which is a hardware device. The MMU uses following mechanism to convert

virtual address to physical address.

The value in the base register is added to every address generated by a user process which

is treated as offset at the time it is sent to memory. For example, if the base register value

is 10000, then an attempt by the user to use address location 100 will be dynamically

reallocated to location 10100.

The user program deals with virtual addresses; it never sees the real physical addresses.

Swapping

Swapping is a mechanism in which a process can be swapped temporarily out of main

memory to a backing store, and then brought back into memory for continued execution.

Backing store is a usually a hard disk drive or any other secondary storage which fast in

access and large enough to accommodate copies of all memory data for all users. It must

be capable of providing direct access to these memory images.

Major time consuming part of swapping is transfer time. Total transfer time is directly

proportional to the amount of memory swapped. Let us assume that the user process is of

size 32KB and the backing store is a standard hard disk with transfer rate of 1MB per

second. The actual transfer of the 32K process to or from memory will take


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32KB / 1024KB per second

= 1/32 second (0.03125 second)

= 31.25 milliseconds

Process Po

Process P1

1

2

Swap out

Swap in

Operating System

User space

Main memory Backing store

Memory Allocation

Main memory usually has two partitions namely:

Low Memory -- Operating system resides in this memory.

High Memory -- User processes are held in high memory.

Operating system uses the following memory allocation mechanism.

Fragmentation

As processes are loaded and removed from memory, the free memory space is broken into

little pieces. It happens after sometimes that processes cannot be allocated to memory


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blocks considering their small size and memory blocks remains unused. This problem is

known as Fragmentation. The fragmentation is of two types:

External fragmentation can be reduced by compaction or shuffle memory contents to place

all free memory together in one large block. To make compaction feasible, relocation

should be dynamic.

Paging

External fragmentation is avoided by using paging technique. Paging is a technique in

which physical memory is broken into blocks of the same size called pages and represented

in power of 2. When a process is to be executed, it's corresponding pages are loaded into

any available memory frames. Operating system keeps track of all free frames. Operating

system needs n free frames to run a program of size n pages.

Address generated by CPU is divided into:

Page number (p) -- page number is used as an index into a page table which contains base

address of each page in physical memory.

Page offset (d) -- page offset is combined with base address to define the physical memory

address.

The following figure shows the paging table architecture.


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Segmentation

Segmentation is a technique to break memory into logical pieces where each piece

represents a group of related information. For example, data segments or code segment for

each process, data segment for operating system and so on. Segmentation can be

implemented using or without using paging.

Unlike paging, segments are having varying sizes and thus eliminate internal

fragmentation. External fragmentation still exists but to lesser extent.

Address generated by CPU in terms of segments can also be divided into two:

Segment number (s) -- segment number is used as an index into a segment table which

contains base address of each segment in physical memory and a limit of segment.

Segment offset (o) -- segment offset is first checked against limit and then is combined

with base address to define the physical memory address.


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INPUT AND OUTPUT DEVICES

The devices which are used to input the data and the programs in the computer are known

as "input devices". Input device can read data and convert them to a form that a computer

can use. Output devices can produce the final product of machine processing into a form

usable by humans. Input and Output (I/O) devices provide man to machine communication.

Some of the input devices are explained below:

(i) Keyboard (ii) Mouse (iii) Scanner (iv) Track Ball (v) Light Pen (vi) Optical

Character Rader (OCR) (vii) Bar Code Reader (viii) Voice Input Systems (ix) Digital

Camera

Output Devices

(i)

Monitor (ii) Printers (iii) Plotters (iv) Speakers (v) Projectors (vi) Buzzers

(vii) Earphones and headphones (viii) Braille embosser

References

Arthur, C. (2012). "Windows 8 will run on ARM chips - but third-party apps will need

rewrite". The Guardian. P 23 - 26

Chris, S. (n.d). Introduction to operating systems. Retrieved on October 20, 2015 from

http://staff.um.edu.mt/csta1/courses/lectures/csm202/os6.html

Dhotre, I. A. (2009). Operating Systems. Technical Publications. p. 102.

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Poisson, Ken. "Chronology of personal computer software". Retrieved on retrieved on

12th September, 2013.

Salako, E. A. (2011). Introduction to computer operating system for secondary schools.

An unpublished textbook.

Stallings, D. (2005). Operating systems, internals and design principles. Pearson:

Prentice Hall. p. 6 - 8.

Stallings, D. (2008). Computer organization & architecture. New Delhi: Prentice-Hall

of India Private Limited. p. 267. ISBN 978-81-203-2962-1.

Victor, G. (2010). "Operating system market share". Net applications. Retrieved on 5th

November, 2009.
http://www.islandnet.com/~kpolsson/compsoft/soft1998.htmhttp://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/Special:BookSources/978-81-203-2962-1http://en.wikipedia.org/wiki/Special:BookSources/978-81-203-2962-1http://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://www.islandnet.com/~kpolsson/compsoft/soft1998.htm

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