Introduction to CPU Scheduling

Summary

This lecture introduces CPU scheduling as a fundamental concept in operating systems, essential for maximizing computer productivity. It explains the importance of CPU scheduling in multi-programmed systems, where the operating system efficiently allocates the CPU among processes to avoid idleness. The lecture promises to delve into various CPU scheduling algorithms, their differences, and performance in specific scenarios, aiming to clarify the topic for students preparing for computer science exams.

Takeaways

• 📚 CPU scheduling is a crucial topic in operating systems and is often a focus in computer science exams.
• 💡 The purpose of CPU scheduling is to improve computer productivity by efficiently managing the CPU among multiple processes.
• 🔄 CPU scheduling is fundamental to multi-programmed operating systems, allowing for more than one process to run simultaneously.
• 🤔 The concept of switching the CPU among processes can be confusing at first but will become clearer with further study.
• 🛠️ Different CPU scheduling algorithms exist, each with its own method for assigning CPU time to processes and managing wait times.
• 🔍 The effectiveness of these algorithms varies depending on the situation, and understanding them is key to efficient CPU scheduling.
• 🖥️ In single-processor systems, only one process can run at a time, leading to idle CPU time when processes wait for I/O operations.
• 🔑 The goal of multiprogramming is to ensure that the CPU is always in use, maximizing utilization by running processes concurrently.
• 🔄 When a process requires I/O and must wait, CPU scheduling allows the operating system to allocate the CPU to another process, avoiding idle time.
• 🕒 CPU scheduling involves creating a schedule to determine which process gets the CPU and for how long, optimizing overall system performance.
• 📝 The lecture series will delve into the specifics of CPU scheduling, including terms, methods, and various algorithms used to manage CPU time allocation.

Q & A

What is CPU scheduling?

CPU scheduling is the process of allocating the CPU to different processes in a multiprogrammed system to make the computer more productive by avoiding idle time.

Why is CPU scheduling important in operating systems?

CPU scheduling is important because it is the basis for multiprogrammed operating systems, allowing the operating system to switch the CPU among processes to maximize productivity and avoid CPU idleness.

What is the main objective of multiprogramming?

The main objective of multiprogramming is to have at least one process running at all times to maximize CPU utilization and minimize idle time.

How does CPU scheduling improve productivity in a computer system?

CPU scheduling improves productivity by ensuring that the CPU is always utilized by some process, even when one process is waiting for IO operations to complete.

What happens in a single processor system when a process needs to wait for IO operations?

In a single processor system, when a process needs to wait for IO operations, the CPU may sit idle, wasting time and reducing productivity.

What is the difference between a single processor system and a multiprocessor system in terms of process execution?

In a single processor system, only one process can run at a time, while in a multiprocessor system, multiple processes can run simultaneously, improving efficiency.

What is the purpose of having multiple processes in memory during CPU scheduling?

The purpose is to ensure that when one process has to wait, the CPU can be immediately assigned to another process, thus keeping the CPU busy and improving system efficiency.

How does CPU scheduling decide which process should get the CPU or when a process should wait?

CPU scheduling uses different algorithms to determine which process should be assigned the CPU and when, based on various factors such as process priority, waiting time, and resource requirements.

What is the role of CPU scheduling algorithms in operating systems?

The role of CPU scheduling algorithms is to assign the CPU to processes at specific times, determining how long they should wait and ensuring efficient use of CPU resources.

What are the different CPU scheduling algorithms that will be studied in the lecture series?

The lecture series will cover various CPU scheduling algorithms, each with different methods for assigning the CPU to processes and different performance characteristics in different situations.

Why is it necessary to study different CPU scheduling algorithms?

Studying different algorithms is necessary to understand their strengths and weaknesses, and to choose the most appropriate algorithm for specific system requirements and conditions.

Outlines

00:00

📚 Introduction to CPU Scheduling

This paragraph introduces the concept of CPU scheduling, emphasizing its significance in operating systems and computer science exams. It explains that CPU scheduling is fundamental to multi-programmed operating systems, which aim to enhance computer productivity by switching the CPU among various processes. The paragraph outlines the lecture's agenda, which includes an introduction to CPU scheduling, a discussion of different CPU scheduling algorithms, and their performance in specific situations. It also touches on the basics of single processor versus multiprocessor systems and the goal of multiprogramming to maximize CPU utilization.

05:02

🔄 The Need for CPU Scheduling

This paragraph delves into the necessity of CPU scheduling to prevent the CPU from idling during processes that require I/O operations. It describes how in a single processor system, the CPU remains idle while waiting for I/O completion, leading to wasted time and reduced productivity. The paragraph explains the concept of multiprogramming, where multiple processes are kept in memory, allowing the CPU to switch to another process when one is waiting for I/O. This approach ensures that the CPU is always utilized, thereby improving efficiency. The paragraph also introduces the term 'scheduling' in the context of CPU scheduling, highlighting the role of various algorithms in determining process execution times and CPU assignments.

10:03

🎵 Conclusion and Transition to Next Lecture

The final paragraph of the script is a brief musical interlude, signaling the end of the current lecture and the transition to the next part of the series. It serves as a pause for the audience to reflect on the information covered and prepares them for the upcoming detailed exploration of CPU scheduling concepts, terms, and algorithms in the subsequent lectures.

Keywords

💡CPU Scheduling

CPU Scheduling is the process of selecting which process to run on the CPU based on various algorithms. It is central to the theme of the video, as it is the method by which operating systems manage the execution of multiple processes to maximize computer productivity. The script mentions that CPU scheduling is the basis of multi-programmed operating systems and is essential for making the computer more productive by avoiding idle time.

💡Operating System

An operating system is a set of software that manages computer hardware resources and provides various services. In the context of the video, the operating system plays a crucial role in CPU scheduling, deciding which process gets the CPU at what time and for how long, ensuring efficient resource utilization.

💡Multi-Programmed Operating Systems

Multi-programmed operating systems are designed to run multiple processes concurrently. The video emphasizes that these systems work on the principle of CPU scheduling, allowing for better utilization of the CPU by switching it among different processes, thus improving productivity.

💡Process

In computing, a process is a program in execution. The script uses the term to describe the individual tasks that the CPU can execute. CPU scheduling is about deciding which process should be given access to the CPU to execute, especially when one process is waiting for IO operations.

💡Productivity

Productivity, in the context of the video, refers to the efficiency and effectiveness with which the CPU is utilized. The goal of CPU scheduling is to improve productivity by ensuring that the CPU is always performing some task, thus avoiding idle time.

💡Single Processor System

A single processor system is a computer system with only one CPU. The script contrasts this with multiprocessor systems, explaining that in a single processor system, only one process can run at a time, which can lead to inefficiencies if the process is waiting for IO operations.

💡Multiprocessor Systems

Multiprocessor systems are computer systems with multiple CPUs. The video script highlights the advantages of such systems, where more than one process can run simultaneously, which is more efficient than single processor systems in terms of CPU utilization.

💡CPU Utilization

CPU utilization refers to the percentage of time the CPU is active and being used for processing tasks. The script discusses the objective of multiprogramming to maximize CPU utilization, ensuring that the CPU is always engaged in some process execution to avoid idle time.

💡IO Operations

IO Operations, or Input/Output operations, are the processes by which a computer system communicates with external devices. The script explains that when a process requires IO operations, it must wait, potentially causing the CPU to be idle if not managed by CPU scheduling.

💡Scheduling Algorithms

Scheduling algorithms are the methods or rules used by the operating system to decide which process gets the CPU. The video mentions that there are various algorithms for CPU scheduling, each with different ways of assigning CPU time to processes, which will be explored in more detail in the subsequent lectures.

💡Idle Time

Idle time refers to the period when the CPU is not performing any task and is essentially waiting. The script discusses the inefficiency of idle time in single processor systems, where the CPU sits idle while a process is waiting for IO operations to complete, and how CPU scheduling can help to reduce this downtime.

Highlights

CPU scheduling is a crucial topic in operating systems and important for computer science exams.

CPU scheduling is fundamental to multi-programmed operating systems, enhancing computer productivity.

The concept of switching the CPU among different processes to improve productivity is introduced.

Different CPU scheduling algorithms will be covered, each with unique ways to manage CPU assignments.

The importance of understanding CPU scheduling for its role in maximizing CPU utilization.

Single processor systems can only run one process at a time, leading to potential CPU idle time.

Multiprocessor systems allow for more simultaneous process execution, improving CPU utilization.

The objective of multiprogramming is to keep a process running at all times to avoid CPU idleness.

CPU scheduling aims to prevent wasted time when a process is waiting for IO operations to complete.

The necessity for CPU scheduling to avoid idle time and improve system efficiency is discussed.

CPU scheduling allows for multiple processes to be kept in memory, ready to utilize the CPU when needed.

When a process waits, the operating system reallocates the CPU to another process, maintaining efficiency.

The process of determining which process should get the CPU and when is managed by CPU scheduling algorithms.

CPU scheduling is likened to preparing a daily schedule, assigning specific times for tasks.

Different CPU scheduling algorithms will be explored in detail in upcoming lectures.

The basics of CPU scheduling are explained to set the stage for a deeper dive into specific algorithms.

The practical applications of CPU scheduling in improving system performance are emphasized.

Transcripts

in this lecture we'll be starting to

study about CPU scheduling CPU

scheduling is a very important topic in

operating system and it is a topic that

you should really know about whether you

are studying about operating system in

general or if you are preparing for any

exams of computer science in which

operating system is a subject then this

is a topic from which you may get many

questions so this is a really important

topic and let us try to understand and

see what is the CPU scheduling and what

it does CPU scheduling is the basis of

multi programmed operating systems and

by switching the CPU among processors

the operating system can make the

computer more productive multi program

operating systems they work on the basis

of the CPU scheduling and why is that

and that is because by switching the CPU

among processors the operating system

can make the computer more productive

now you may be thinking why did we say

by switching the CPU among processes so

this is the actual thing that is going

to happen in CPU scheduling we are going

to switch the CPU among different

processes and thereby we are going to

see how the productivity of our computer

is going to improve so don't worry even

if you don't understand what this means

right now

it will become clearer when we go into

the details of CPU scheduling so now let

us see what are the important topics

that we need to cover under this topic

of CPU scheduling so the first thing

that we are going to do is to introduce

CPU scheduling which is the basis of

multi programmed operating system so I

already told you that CPU scheduling is

the basis for multi program operating

systems so we will introduce if you

scheduling and see what it actually

means what it actually does and how it

makes our computer more productive and

secondly we are going to describe the

various CPU scheduling algorithms so

there are different ways in which CPU

scheduling can be done so we will see

the various algorithms that we have

which helps in accomplishing CPU

scheduling and we will see how these

algorithms differ from each other and we

will see which of these algorithms

perform better in particular situations

so these are the main

topics that we are going to cover first

of all will study what CPU scheduling is

then we will look into the algorithms so

these two topics are very important and

we will try to go into the details of

these topics and we will try to make CPU

scheduling very clear to all of us so

before we delve into the details of CPU

scheduling let's first get the basics

right let us first try to understand in

a very basic and in a very simple way

what CPU scheduling means and then we

will see what is the importance of CPU

scheduling and after getting the basics

right and after trying to understand it

in a simple way we will go into the

details in the coming lectures so coming

into the basics let's talk a bit about

single processing systems and

multiprocessor systems which we have

already studied before in this lecture

series so in a single processor system

only one process can run at a time so we

know that in a single processor system

there is only one processor in that one

processor only one single process can

run at a time and any other processes

must wait until the CPU is freed and can

be rescheduled so when one process is

running we have to wait until that

process is completed and only after that

any other process that is waiting can be

given the CPU for its own execution so

this is what happens in single processor

systems but we already saw that we have

multiprocessor systems as well so

multiprocessor systems were much better

because there are more number of

processors and hence there can be more

number of processes running

simultaneously at the same time so the

objective of multi programming

is to have some process running at all

times to maximize the CPU utilization so

we know that the objective of

multiprogramming is that we want some

process to be running at all the times

so that the CPU is always utilized by

some process so a process is executed

until it must wait typically for the

completion of some IO request so when a

process is being executed that say that

it is using the CPU it is using the

processor the CPU

it is being executed and that process is

in hold of the processor and what

happens is that when that process needs

some are your executions to be done then

what happens it requests for the i/o

operations to be performed that is

input/output operations to be performed

and until and unless an i/o operation is

not complete it has to wait so while it

is waiting what happens is that it is

still in hold of the processor but it is

not using that processor because it is

waiting for the i/o operation to be

completed first so what happens is that

in a simple computer system the CPU then

just sits idle and all this waiting time

is wasted and no useful work is

accomplished so when a process is in

hold of the processor and while

execution was being done if that process

needed some IO request to be complete

then it has to wait for that IO request

to be complete and while it is waiting

for it to be complete it is still having

that processor with it but it is just

waiting and that processor is not being

used at that time so the CPU is just

sitting idle and then all the time that

it is sitting idle that time is wasted

because nobody is using the CPU at that

time hence we see that there is going to

be a decline in our productivity because

of this factor that we have seen here so

the basic need for CPU scheduling is to

avoid this we don't want the CPU to sit

idle at any time so what we want is that

if there are processes available then we

want the CPU to be utilized as much as

it can be we don't want the CPU to sit

idle so in order to accomplish this we

are going to introduce CPU scheduling so

with multi programming we try to use

this time productively and what do we

mean by this time this time is a time

that we talked about here which is a

time that is wasted when the CPU is not

doing any useful work so we want to make

use of this time with multi programming

and make it productive so let's see with

the help of CPU scheduling how are we

going to be able to make this time

active so what we are going to do is

that several processes are kept in

memory at one time so instead of having

just one process we will be having

several processes kept in memory at one

time and then what happens when one

process has to wait the operating system

takes the CPU away from that process and

gives the CPU to another process and

this pattern continues so we saw that in

the simple computer system when one

process is waiting for some IO request

to be complete then the CPU is not being

utilized so what we are going to do is

that when one process has to wait the

operating system will take the CPU away

from that process because that process

is not using that CPU at that particular

time and what will it do

it will give that CPU to another process

and then this pattern continues so the

processor or the CPU is taken away from

that process that is waiting and it is

given to another process that process

can make use of the CPU at that time for

its own execution and this pattern

continues that means whenever somebody

that is some process has to wait the CPU

will be taken away from them and it will

be given to some other process so that

is what happens and in that way we see

that we can make the computation more

efficient because the CPU will not sit

idle it will always be utilized by some

or the other process when we are doing

this thing what happens is that how do

we determine which process should get

the CPU or which process should wait or

after how long should a process be given

a CPU all these things are going to be

done and explained by CPU scheduling

let's try to understand from the name

itself CPU scheduling scheduling what do

you mean by scheduling scheduling means

we are trying to assign a particular

time for doing a particular task so you

may prepare your schedules your

day-to-day schedule that at this time I

will be doing this thing and at this

time I will be doing this thing so you

are preparing a time schedule for

yourself so in the same way the

operating system will prepare a schedule

as of which process should get

CPU at what time or how long should they

wait and things like that so this is the

place where CPU scheduling comes into

picture so we may think that what is the

role that CPU scheduling follows in

order to accomplish this task so there

is not just one CPU scheduling rule but

there are many rules so depending upon

the situation we may use one of these

rules so that is what I talked about the

different algorithms of CPU scheduling

that I said in the beginning of this

lecture so different algorithms will

have different ways of assigning the CPU

to different processes and different

times we will be studying those

algorithms one by one and we will see

how CPU scheduling happens in these

different algorithms so with this I hope

the very basics of CPU scheduling is

clear to you and I hope you understood

why we need CPU scheduling and from the

next lecture onwards we will be going

into more details of CPU scheduling

trying to understand the terms and

trying to understand the ways and also

the different algorithms and we will see

how CPU scheduling is done so I hope

this was clear to you thank you for

watching and see you in the next one

[Applause]

you

[Music]