System Calls

[@hoangminhchau2187]

There are 2 modes of execution for a program: 1) User mode: - Do not have access to resources like memory or hardwares - When a program crashes, the entire system will not break down 2) Kernel mode: - Privilidged mode - Have access to resources - When a program crashes, the entire system breaks down Because user mode is safer, most programs run in user mode. But some programs might need access to resources, so they will make a call to the OS to request for these. This call is system call. When the OS receives the system call, it will change the mode of the program to kernel mode. This is called context switching.

[@Madhavi_1177]

🎉

[@jeanxza5395]

Called mode shifting not context switching he made a mkstake

[@inishkohli273]

"Because user mode is safer, most programs run in user mode".. It maybe better to say , most program are REQUIRED to run in user(restricted mode) by the parent of the computer(OS) because this kid from neighbor house(programs created by third party developer) can break and crash things(crash system) when they come to play in our house(run in our OS) , they can steal things(privacy issues from external programs) .. However our own kid( OS system default apps or programs like Ms Word, ... has loose to no restriction) because we gave birth to our kid, we can easily correct their behavior....(fix bug of system apps) ...>....Sorry but my analogy is weird.🤣

[@Subhasini_Sethi]

​@@inishkohli273😂😂😂😂

[@mathy642]

@@jeanxza5395It can be mode switching/context switching

[@narendrachintala7998]

Switching from kernel to user and vice versa is known as mode shifting not context switch. Context switch is the one which happens between 2 processes.

[@srinivaspokala333]

Correct

[@mehulkumar3469]

Right

[@tusharparashar1879]

Yups that's why I was confused when he said context switching

[@AdithyaKahawanugoda]

true

[@hetaeramancer]

Can you guys give an example of a context switch?

[@bekacynthia]

The first three and a half minutes of your explanation helped me understand something I was reading and reading but was not grasping it entirely. Thank you for the lesson.

[@raviiMaurya]

same

[@Mr_Memer01_]

Exactly 💯

[@fakeskillerog9979]

Absolutely 💯

[@mrbrian826]

Very happy to find an explanation in English that is easy to understand. Many thanks from Ireland 🤝

[@bradleytimm5349]

I'm pretty sure 10% of India's GDP consists of English Language CS related tutorial videos.

[@hhcdghjjgsdrt235]

@@bradleytimm5349 rest 90% of gdp consist of the salary of Indian software engineers who can speak English.

[@vikassaini7485]

@@hhcdghjjgsdrt235 😂😂

[@munisasidhar4897]

Yes

[@AS-ne5wu]

Had to rewatch this several times since it's a difficult topic for beginners, but understood everything in the end. Amazing how just one video gives so much info.

[@trilecao9014]

Thanks! 1. User mode: safer 2. Kernel mode: more privilege

[@Mehraj_IITKGP]

What I learnt from the lecture: User mode and kernel mode refer to two different modes of operation for a computer's processor and operating system. User mode is the mode in which user applications and programs operate. In user mode, the processor can access only a limited set of resources and instructions, which are defined by the operating system. This includes memory, input/output devices, and CPU registers. User-mode applications do not have direct access to the system's hardware or kernel memory, and any attempt to access such resources will result in an error. On the other hand, Kernel mode is a privileged mode in which the kernel operates. In kernel mode, the processor has access to all system resources, including hardware devices and kernel memory. This allows the operating system to perform low-level operations and interact with hardware devices directly. System-level processes, such as device drivers and system services, operate in kernel mode. A system call is a call made by a program to OS in order to access certain resources which are not accessible in the user mode. So in brief, we can say that a system call is special call made by a program to switch from user mode to kernel mode in order to access certain resources. This is known as mode-shifting, not context switching as the instructor mistakenly called it context switching. The term "context switching" usually refers to the process of saving and restoring the context (i.e., state) of a process or thread so that it can be temporarily suspended and later resumed by the operating system. The term "mode switching" or "mode transition" may be more appropriate to describe the process of switching from user mode to kernel mode and back again. When a user-mode program makes a system call to the operating system, the following steps occur: 1. The user-mode program issues a system call request, typically through a library function provided by the operating system or through an interrupt instruction. 2. The processor switches from user mode to kernel mode, which involves saving the current state of the user-mode program, including its register values and program counter, onto the kernel stack. 3. The operating system identifies the requested operation, validates the arguments passed by the user-mode program, and executes the operation on behalf of the user-mode program. This may involve allocating or releasing resources, modifying data structures, or performing I/O operations. 4. Once the operation is completed, the operating system saves the results of the operation, restores the saved context of the user-mode program from the kernel stack, and switches back to user mode. 5. The user-mode program resumes execution at the point where the system call was made, and the results of the system call are made available to the program.

[@Ahnos]

Thanks for the notes

[@TechnoyashBro]

🥳 Tqsm sir from india 🇮🇳

[@sheetalyadav4483]

Thank you sir ! I'm grateful that you're my teacher

[@quratraja7391]

Great job Tutorial explains about system calls. System call is the call made by a program running in user mode to the kernel of the operating system to switch the program from user to the kernel mode so that it can access required resources. An example of copying contents from one source file to a destination file is given. This small task involves lots of system calls.

[@jamal8916]

You have explained this complex topic in the most amazingly simple manner, excellent teacher kind sir!

[@noviljohnsonnovil1676]

u've got really great patience. n thanks a lot.

[@MrKristian252]

for [name of some hardware], you need a [big pause] *system call* This is now burned into my brain, thank you so much for this explanation surrounding the topic!

[@Hero360-k1e]

I watch this video for 2 hours, I can't focus😢😢😢

[@dhanarsantika]

Nice explaination, you made it simple

[@ishajaswal7547]

Very well explained

[@pieetro_o]

System Call. Generate Thermal Element. Form Element. Arrow Shape. Fly Straight. Discharge.

[@YashDEVELOPER12]

You are a great teacher sir.. God bless you always and thanks alot from bottom of my heart❤

[@codextreme7756]

Switching from user mode to kernel mode is not a context switch it just a mode switch. When making a system call there is no context switch because you are in the same address space using the same page table.

[@saadmanahmed860]

thanks to u for correcting the concept

[@chintupatelyt2668]

Awesome sir Keep Go’ing

[@Unxon-g1l]

bohut bhadiya videos bna rhe ho thank you sir

[@trishna1051]

Thank u very much.. Really it's very easy to understand after watching ur Vedios.. It helps me a lot...

[@coding_unicorn2]

Your explanation is so easy to understand the topics which appears difficult 😊❤

[@bhoopendrafagna8535]

very easy way of explaining thanks a lot sir

[@hotfirefly]

Damn sys call for each and every step

[@paulinov.rodriguesmuebe6744]

Nice explanation. Huggs from Mozambique

[@jawadashraf3181]

Dear, transfer from user mode to kernal mode is not context switching. please correct it in video. Context switching involves processes only.

[@nuthankumar6138]

agree

[@saadmanahmed860]

good illustrations

[@mazharkhaliq1971]

With the level of knowledge you always amaze me 😊, thanks for the video

[@f2pethereum67]

Haha thanka alot sir my teacher teaches everything from your automata lectures but you explain better and today your example was the answer to my os assignment thanku sir really appreciated ❤️

[@chaturadh]

Your explanation is really good. Could you please make a video about fork(),exec() and wait() function, it is really hard to understand Thank you

[@ekc133]

System Call Interfaces (SCI) are the only way to transit from User space to kernel space.Not context switching

[@dinushachathuranga7657]

Thanks a lot for the nice explanation❤

[@atharislam282]

i have done my lecture bcoz of u'r help

[@VASAVILATHACSE2022VelTechChenn]

There are 2 modes... 1.user mode-mode bit 1 2 .kernel mode-mode bit 0 User mode: It doesn't contain any resourses. It's mode bit is 1 If the program crashes entire system is not collapsed.hence,it's safe mode to use Kernel is priviliged mode Bit mode is 0 If program crashes whole sys collapses So not safe,recommended to use

[@narendrarudra3543]

THANK YOU

[@agamgill9563]

great job....thank u so much sr..

[@kallipalliashokkumar8114]

Explanation is very well

[@majki5900]

awesome explanation, that was very helpfull :) !

[@mohsinabdulrauf9145]

Yours course was very helpful to me sir i am grateful to you

[@vijaysharma-nn9th]

wonderful explanation

[@MN-lz6lf]

سبحان الله و بحمده . . ♥️ سبحان الله العظيم . . . 💙

[@mukhtiarahmad7448]

sir, method of explanation is excellent.........

[@Bb-307]

Amazing.. great teacher

[@khaliidcaliy1056]

User mode and kernel mode is cpu execution mode so, Context switching is can be triggered by alot of things such as interrupt handling in that case context switch may occur for example if there were process of iowaiting state then disk controller will trigger interrupt send to cpu and interrupt handler invoked causing context switching. Context switch is not only for kernel user mode

[@smohammadhn]

very clear explanation

[@thareejanp3933]

Switching User mode to kernel mode called as System Call Interfaces (SCI) Not context switching by the time, context switching will happen while switching to another process

[@MMX17]

It kind of sounds like a system call is just a method called by the OS. Like in C++ a cout statement is used to display something to the screen, but in your explanation you mention a system call is used to make that happen.

[@surajgahatraj3233]

perfect explaination!

[@mohsinabdulrauf9145]

there is little bit mistake except of switching terminology you can say there is trap generated in a program goto kernel mode from user mode as it is taught me by my class teacher thanks else everything you guide right sir thanks!

[@shaikzuhair8537]

Good explanation...

[@maitreyamoharil4299]

Great explaination sir 😊 Thank you 🙏

[@amjadalsobhi7388]

Thank you so much 🌷🌷

[@patricechaula3430]

I have always to stick to reading books and avoid youtube videos. Thanks for the tutorial, you explain it very well.

[@harishovandkar1708]

GREAT LECTURE SIR

[@mvakamusic758]

Well explained thanks so much

[@sona854]

very nice explain

[@humairaahmadi4759]

very clear and simple explaination .thanks alot sir for this all sach a efficiency that u have provide for us to learn it in great way. lots of love from afghanistan .❤🌻🌷🌺

[@moonyt7033]

Looks like someone has graduated. Congrats sister 🎉

[@juliannafotheringham7101]

angel, thank you

[@atharislam282]

thanku..

[@sugatasaha4423]

great explanation.

[@sreepriyanks]

well explained...thank u

[@Dragonborn-dc4uj]

It can also take control of someone and make a army and make you a god basically

[@rupaligaikwad20aug]

Thank you for great knowledge 🙏

[@klaik30]

It is first explained that if a program is in kernel mode and crashes, the whole system crashes. Then it is defined that a mode shift happens in an instant when a system call is made. Then finaly it is shown that almost EVERYTHING is a system call. Just getting input and showing it on the screen are system calls. The thing is that obviously your whole system would not crash if something in that program crashes even though every action is a system call. How can that be?

[@mohammedfaizal3577]

Worked, thx

[@vmorita]

Thank you

[@manjunathkotabal]

great lecture sir , continue doing the same

[@Mohsinsadiqko]

So perfect

[@Wickykhan]

thank u sooooooo much

[@aatmakumar4631]

Nice class

[@yerramachusreenu1197]

Nice session .better explanation. Make some more videos

[@bhagirathsinhmakwana6085]

Sir if an user mode switch to the kernel mode then there is chances of system crashes . Then why there is context switching?????

[@syedhabeebuddin101]

Thanks !

[@انميانمي-ن7ن]

Why do we switch from the user's stack to a kernel stack when we enter the kernel ( e.g. for a system call ) ? @Neso Academy

[@章魚-l8y]

good explaination! However, seems all action that perform in the copying procedure are system calls (need to switch to kernal mode). Is there any example of user mode action?

[@munteanionut3993]

Thank you for the video! 05:20 is a bit misleading. You first mention we initially get the file name through the "Acquire Input Filename" step, but then you also mention "Then you are displaying a prompt to the screen, asking the user to enter the name of the input file". Didn't we already do step 2 at step 1? Or is this just a terminology issue and what you actually meant with the first step is that: we get the memory required to store the input first AND AFTERWARDS we get the literal input..?

[@hajji384]

The Best details concepts I have ever watched. 🤩😍🎉✨

[@dhanushsivajaya1356]

Thankyou sir

[@varunsood7899]

Nice lectures 👍👍 sir you are clearing all my doubts

[@abhinayreddy5499]

Tqs alot sir...i like ur videos...and it helped me alot...but our exams r starting on april 16th...so plz upload bit faster...

[@fousizadizusa8524]

Thanks alot sir 😊

[@siddhu-46]

Nice explaination Awesome. But switching from user mode to kernal mode is Known as Mode shifting based on PSW(program status word) mode bit it changes to user mode to kernal mode ??

[@basitobaid6903]

Good explanation brother but you said program shifts from user mode to kernel mode but it's actually a process that shifts (As the running program is called the process ) so you better correct it!

[@brandonyangeh602]

thanks

[@NAAR47]

U r great , keep going

[@linoymiz22]

thank you!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[@ayushiydvKG]

thnx sir

[@mrkiwiboy2011]

Hi, do you mean operating system needs system call to write completion message to screen? I am pretty sure user has nothing to do with it so please explain why you say "you" in this video all the time instead of Operating system!

[@sfcguy8300]

tq sir

[@praneshacharya6115]

what does happen if crash occur during mode switching?

[@nrgs-alh]

Hi thanks for your amazing explanation, i have a question. It means that for all the commands and operations which are in user mode, the system call is being used? And is it related to the CPU? I mean if this happens, it takes so much time from the cpu to do these system calls.

[@andreborges8640]

don't you need to close the input file?

[@serawang8830]

I am confused about why there is a system call for "Acquire input filename". I think "Write prompt" and "accept input" is just acquiring the input filename. Can anyone explain? thx!

[@developer9172]

I dont undrstand Your Question Can You Explain me??

[@j.hendrix3989]

I have the same question

[@vikyathvicky3886]

because for acquiring a file name,we need to write it through keyboard(which means device access or hardware access)...so you need to request this service of accessing hardware devices from kernel of the os

[@varun300690]

I too could not understand this. Has there been any resolution, if you understand it now, then please share your insight.

[@nooratal3739]

👍👍👍

[@be_55_atharvsankpal38]

In short change of mode is called system call Correct me if i am wrong

[@developer9172]

is it ture??

[@be_55_atharvsankpal38]

@@developer9172 os does not get access to various files so it enters in Kernel Mode (km) has full access the change of mode is called Kernel mode

[@developer9172]

@@be_55_atharvsankpal38 Yeah right

[@developer9172]

@@be_55_atharvsankpal38 Thnx alottt for thz

[@zyanchuah]

system call generate luminous element nvm

[@ripunjoysahariah9634]

sao

[@YashDEVELOPER12]

Sir I have a doubt , before creating output file. Why not I can check , if the output file exist in the memory .. why we are creating output file without checking.. plz clear this doubt!

[@IshuSingh-k7f]

Can anybody give an example of something which is not considered a system call? Seems like every task is a system call