What is a Process in an Operating System?

Summary

This lecture delves into the concept of a process in operating systems, explaining its role as a unit of work and its lifecycle through various states such as new, ready, running, waiting, and terminated. It highlights the importance of the operating system in managing processes, the function of the scheduler in process execution, and the concept of preemptive multitasking with time slices for CPU usage. The lecture also touches on the trade-offs between responsiveness and performance in different system types and introduces the process control block that stores essential information about each process.

Takeaways

• 💻 The operating system (OS) acts as the first software layer on top of the hardware, managing applications and system resources.
• 🔧 The OS is responsible for task management, which includes executing programs on the CPU, either by user initiation or the OS itself.
• 📝 A program must be compiled into an executable format like a .jar or .exe file before it can be run on the CPU.
• 🚀 When an executable file is launched, the OS creates a process object in memory, which it manages throughout its lifecycle.
• 🔑 A process is defined as an instance of a program loaded into memory, representing a unit of work in the OS.
• 🌀 A process has various states, starting with 'new', transitioning to 'ready', and then to 'running', 'waiting', and finally 'terminated'.
• ⏱️ The scheduler is a dedicated OS component that selects processes to run on the CPU, implementing preemption to manage CPU time among processes.
• 🔄 Preemptive multitasking allows the CPU to execute parts of different processes in intervals, preventing any single process from monopolizing the CPU.
• 📊 The number of CPU cores affects the system's throughput; more cores allow more processes to run in parallel.
• 🕒 The time limit for CPU usage by a process is known as a time slice, which is crucial for balancing process execution and system responsiveness.
• 🔄 Context switching is the process of changing the currently running process on the CPU, which can impact performance if frequent.
• 🗂️ The process control block (PCB) stores vital information about a process, including its state, ID, privileges, scheduling info, and memory allocation.

Q & A

What is the role of the operating system in a computer's architecture?

The operating system acts as the first software layer on top of the hardware, managing the CPU, memory, and devices. It is responsible for task management, security, performance, and other responsibilities, serving as an interface between the hardware and the applications layer.

What is a process in the context of an operating system?

A process is an instance of a program loaded into memory or a unit of work in an operating system. It is an object stored in memory that contains information about the execution of a particular program and is managed by the operating system.

How does a program become executable on the CPU?

A program, which is initially a text file with instructions, needs to be compiled into an executable binary file, such as a .jar or .exe file, which can then be launched by the operating system to create a process object in memory.

What is the initial state of a process when it is created?

When a process is created, its initial state is 'new'. It then transitions to the 'ready' state when it is prepared to be run on the CPU.

What is the role of the scheduler in an operating system?

The scheduler is a dedicated component of the operating system responsible for selecting processes in the ready state and placing them onto the CPU for execution, based on a well-defined algorithm.

What is preemption in the context of process execution?

Preemption is the behavior where the operating system moves a running process back to the ready state to allow other processes to use the CPU. This ensures that the CPU is shared among multiple processes.

What is the purpose of the waiting state in a process's lifecycle?

The waiting state is when a process needs to wait for some external resources, such as data received over the network. During this state, the process is not executing on the CPU but is waiting for the required resources to become available.

How does having multiple CPU cores affect the system's throughput?

Having multiple CPU cores allows the system to handle multiple processes in parallel, effectively tripling the throughput if there are three cores, as each core can execute a process simultaneously.

What is preemptive multitasking and why is it important?

Preemptive multitasking is a mechanism where the CPU executes small parts of different processes at different times, rather than running a single process for a long duration. This ensures that the system remains responsive and can handle multiple tasks concurrently.

What is a time slice in the context of process execution?

A time slice is the specific time limit during which a process is allowed to use the CPU. This value, typically around 100 milliseconds on Linux, is dynamically adjusted by the operating system to manage the execution of processes.

What is a context switch and why is it significant?

A context switch is the operation of changing the process that is currently running on the CPU with another process. It is significant because it allows for multitasking and efficient CPU usage, but it can also impact performance due to the overhead involved in saving and loading the state of processes.

What information is typically stored in a process control block?

A process control block contains the current state of the process, a unique ID, privileges specifying resource access, a pointer to the next instruction, CPU register data, scheduling information like priority, virtual memory allocation, a pointer to the parent process, and information about file descriptors used by the process.

Outlines

00:00

🖥️ Understanding Processes and Task Management in Operating Systems

This paragraph introduces the concept of a process in an operating system, explaining its role within the computer's architecture. It describes the operating system as a complex component that manages tasks, which are programs to be executed on the CPU. The process lifecycle is detailed, starting from the creation of an executable binary file from a program, through the various states a process goes through, such as new, ready, running, waiting, and terminated. The paragraph also explains the role of the scheduler in managing process execution and the concept of preemption, which allows the operating system to manage CPU time among multiple processes. The example of a single CPU core handling multiple processes illustrates the process lifecycle and the impact of having multiple CPU cores on system throughput.

05:02

🕒 Preemptive Multitasking and Process Scheduling

This paragraph delves into the specifics of preemptive multitasking, explaining how it prevents system unresponsiveness by assigning a time limit, known as a time slice, for each process's CPU usage. It contrasts the needs of user-oriented operating systems, which prioritize responsiveness, with server-side systems that favor performance and may allow longer-running processes. The paragraph also discusses the importance of the type of workload in determining the appropriate level of multitasking. It introduces the concept of a context switch, which is the operation of changing the process being run on the CPU, and hints at potential performance issues related to this operation. Lastly, it outlines the information stored in a process control block, which includes the process's state, ID, privileges, pointers, scheduling information, virtual memory allocation, and file descriptors, noting that the exact content may vary by operating system.

Keywords

💡Process

A 'process' in the context of an operating system refers to an instance of a program loaded into memory. It is a fundamental concept in the video, as it represents a unit of work that the operating system manages. The process is not an active entity by itself but contains information about the execution of a program. For example, the script mentions that when a binary file is launched for execution, the operating system creates a process object in memory, which is then managed by the OS.

💡Operating System

The 'operating system' is the first software layer on top of the hardware in a computer's conceptual architecture. It is responsible for managing the hardware resources and providing services to applications. The script emphasizes the operating system's role in task management, creating process objects, and scheduling their execution on the CPU. It is a complex component with various responsibilities, including security and performance.

💡CPU

The 'CPU', or Central Processing Unit, is the hardware component at the bottom of the computer's architecture that executes program instructions. The script discusses how processes are programs that need to be executed on the CPU, which is done by compiling a text file of instructions into an executable binary file. The CPU's role is central to the process lifecycle, as it is where the processes are actually run.

💡Task Management

'Task management' is highlighted as one of the most important responsibilities of the operating system. In the script, it refers to the management of processes, which are programs to be executed on the CPU. This includes creating process objects, scheduling their execution, and handling their various states, such as ready, running, waiting, and terminated.

💡Executable

An 'executable' is a binary file that contains compiled program instructions ready to be run on the CPU. The script explains that a program, initially a text file, must be compiled into an executable format like a .jar or .exe file before it can be executed. This transformation is necessary for the operating system to create a process object from the program.

💡Scheduler

The 'scheduler' is a dedicated component of the operating system responsible for selecting processes from the ready state and placing them onto the CPU for execution. The script describes how the scheduler operates in a single CPU core scenario, picking one process at a time based on a defined algorithm, and how it manages process execution in a multi-core environment to increase system throughput.

💡Process State

A 'process state' refers to the condition of a process at any given time, such as new, ready, running, waiting, or terminated. The script explains the lifecycle of a process, detailing how it transitions between these states from creation to completion. For instance, a process initially in the new state moves to the ready state, then possibly to running, waiting, and finally to terminated.

💡Preemption

'Preemption' is the behavior where the operating system moves a running process back to the ready state to allow other processes to use the CPU. The script describes this as a mechanism to prevent a single process from monopolizing the CPU, ensuring that multiple processes get a chance to execute. It is a key aspect of process management and affects system responsiveness and performance.

💡Context Switch

A 'context switch' occurs when the CPU switches from executing one process to another. The script mentions this in the context of preemption and multitasking, explaining that when the operating system decides to run a different process, it performs a context switch, which involves saving the state of the current process and loading the state of the next process to be executed.

💡Process Control Block

The 'process control block' (PCB) is a data structure that stores information about a process. The script describes the various details a PCB contains, such as the process's current state, unique ID, privileges, pointer to the next instruction, CPU register data, scheduling information, virtual memory allocation, and file descriptors. The PCB is crucial for the operating system to manage and track each process effectively.

💡Time Slice

A 'time slice' is the time limit assigned to a process for its execution on the CPU. The script explains that this mechanism, known as preemptive multitasking, allows the CPU to execute small parts of different processes at various times, preventing any single process from running for an extended period and ensuring that other processes get CPU time. The time slice is an important concept for balancing process execution and system responsiveness.

Highlights

A process is defined as an instance of a program loaded into memory, serving as a unit of work in an operating system.

The operating system is responsible for task management, including the execution of programs on the CPU.

A program must be compiled into an executable binary file before it can be executed on the CPU.

The operating system creates a process object in memory when a binary file is launched for execution.

A process is initially in a 'new' state and transitions to 'ready' when it's prepared to run on the CPU.

The scheduler is a dedicated component of the operating system that selects processes to run on the CPU.

Preemption is the behavior where the operating system moves a running process back to the ready state to allow other processes to use the CPU.

A process can enter a 'waiting' state if it requires external resources, such as data over a network.

The process lifecycle includes states such as new, ready, running, waiting, and terminated.

Having multiple CPU cores allows for parallel processing, increasing system throughput.

Preemptive multitasking ensures that no single process monopolizes the CPU, allowing for a responsive system.

The time limit for CPU usage by a process is known as the time slice, which is typically 100 milliseconds on Linux.

Context switch is the operation of changing the process currently running on the CPU with another.

Process information is stored in a data structure called the process control block, which can vary by operating system.

The process control block contains details such as the process state, unique ID, privileges, and scheduling information.

Different types of systems, like user-oriented or server-side, have different scheduling priorities due to their specific needs.

The lecture provides a comprehensive overview of processes in the context of an operating system, highlighting their lifecycle and management.

Transcripts

all right so in this first lecture we're

going to see what actually is a process

in an operating system

so first if we take a look on the

conceptual architecture of a computer we

know that at the bottom we got the

hardware which contains the cpu the

memory and devices like peripherals and

other external components

on top of that we got the first software

layer in a computer which is the

operating system

and based on that we got the

applications layer which contains all

the applications managed by the user

the operating system is a very complex

component with lots of responsibilities

like security performance and many

others

but probably one of the most important

ones is task management and by task i'm

referring to any program that should be

executed on the cpu which is launched by

the user or by the operating system

itself

so let's see in more detail how this

works

let's say we have a program which is

just a text file with instructions

stored on the local disk

to be able to run it on the cpu we need

to compile it to get an executable

binary file which can be a jar an exe or

any other executable format

that is also stored on the local disk

now when we launch the binary file into

the execution

the operating system will create a

process object that is stored into the

memory in that case

from now on the process will be

completely managed by the operating

system

so if we have to define a process we can

say that a process is an instance of a

program loaded into memory

or more generically a process is a unit

of work in an operating system

keep in mind that a process is not an

active entity it's just an object stored

in memory that contains information

about the execution of a particular

program

a process always has a state when you

create a process its initial state will

be new

when the process is able to be run on

the cpu it will immediately transition

to the ready state

the operating system has a dedicated

component called scheduler which is

responsible for selecting processes from

the ready state and placing them onto

the cpu in order to be executed

the process runs on the cpu for a while

and it can be moved to the ready state

by the operating system when it decides

to let other processes to use the cpu

this behavior is called preemption and

we'll take a closer look on how it works

further in this lecture

a running process can also be moved into

the waiting state if it needs to wait

for some external resources like for

some data that needs to be received over

the network for example

and finally when the process does not

have any other instructions to be

executed it will move to the terminated

state

now let's assume that we have one cpu

core and we got three processes launched

by the user and we want to see how those

processes move through those states

usually if the system has enough

capacity the processes will move

directly to the ready state

the scheduler picks one process based on

a well-defined algorithm and moves it

into the running state

it picks only one process because there

is only one cpu core available

the chosen process runs for a while on

the cpu and then it needs access to some

external resource which may take some

time so it gets moved into the waiting

state

as soon as the cpu is free the scheduler

immediately takes another process and

moves it into the running state

the waiting process receives the data

from the external component and moves

into the ready state ready to be picked

by the scheduler again

the currently running process is

preempted by the operating system

because its time slice has elapsed

and the workflow continues until all the

instructions of the processes are

executed and they move to the terminated

state

this workflow is actually called the

process lifecycle

now if you have three cpu cores for

example we will be able to handle three

processes in parallel which triples the

throughput of the entire system

now let's take a look on what preemption

really is

let's imagine we have a single cpu core

and we have a process that is called

clock which is responsible for simply

printing the current time on the screen

if that process is the only one that is

running on the cpu the system will

become unresponsive because there are

other processes that need to use the cpu

like your browser or the ui components

of the operating system

so to solve that issue each process is

assigned a particular time limit during

which it's able to use a cpu

in that way the cpu will execute small

parts of a process at different times

rather than executing the same process

for a large amount of time leaving space

for other processes to be executed

this mechanism is called preemptive

multitasking and it should always be

preceded with a trade-off in mind

because operating systems that are user

oriented like windows mac os ubuntu and

others need to be responsive so

processes related to ui components are

likely to be scheduled more on the cpu

by leveraging the preemptive

multitasking

on the other hand server-side systems

like windows server or ubuntu server

usually need performance rather than

responsiveness so their scheduler will

likely favor long-running processes

so basically you should have in mind the

type of the workload you're currently

running to see if too much multitasking

can become a problem

now regarding the time limit for which

processes should execute on the cpu

it actually has a name it's called time

slice

and its value is usually 100

milliseconds on linux but it's

dynamically adjusted by the operating

system anyway so you can't really tell

which value it has at any given time

when the process being run on the cpu is

changed with another one

this operation is called context switch

and we'll see in the next lectures why

this operation could become a problem in

terms of performance

now the last important aspect that we

need to know about the process is the

actual information that is stores we

just saw previously that a process lives

in the memory but what it actually

contains

well first it needs to contain the

current state that it has running

waiting terminated or any other state a

unique id which is just a number to

identify the process

some privileges that specify on which

resources the process has access to

a pointer to the next extraction that

needs to be executed

the data that was stored in the cpu

registers when the process was switched

off the cpu

some information related to the

scheduling process like priority for

example

information related to the virtual

memory currently allocated by the

process

a pointer to the parent process and some

information related to which file

descriptors are being used

this data structure is called process

control block

and its content can slightly vary

depending on the operating system

so that's pretty much all you need to

know about the process in the context of

multithreading