How a Single Bit Inside Your Processor Shields Your Operating System's Integrity

In this video we learn about CPU kernel/user operational modes and how the hardware helps software (the operating system) to maintain complete control of the computer.

Content:
00:00 Intro
00:57 CPU operational modes.
02:28 Interrupts
04:02 Op. Mode switching mechanism
04:53 Kernel-mode && User-mode
07:51 Sponsor message
08:34 System calls
13:31 Op. Mode switching mechanism (Summary)
14:14 Cooperative Operating Systems
14:53 Preemptive Operating Systems
16:34 Operating system abstraction
17:03 Kernel-level Drivers
18:37 Kernel-level Software (Rootkit)
19:49 The CrowdStrike disaster
20:20 Spyware concerns with Vanguard
21:08 Video recommendations (for further information)
21:18 Close

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[manojos]

This video answers the exact question that I had when I first studied OS and Computer organization and architecture.

While studying OS we are told that theres something called kernel space and user space and one is more privileged than the other, but never told how this privilege is enforced. At the end of the day if both programs run on the same CPU, using the same hardware, what exactly stops a user program from invoking privileged instructions is a question that plagued me.

When I asked my professor, he answered with one word, "hardware" takes care of it. A very ambiguous useless answer.

Interrupts are hella underrated man, nobody talks about them. Anyway thank you for your video, It will surely help those students who had the same question I had.

[NewbeProgrammer]

Everytime a core dumped video comes out, the world gets 20% smarter. Huge salute to you man, I love your easy to understand and lucid teaching style. Using the information from the previous videos of the ongoing video series on the workings of computers, I have finished building an ultra simple 8 bit computer. You have been like a god when it comes to my quest of learning how computers work deep down. (I'm not in college yet, but I bet this is far more lucid than that)

[drbadzer]

The way you explain OS concepts is above the level of most courses in even the most prestigious universities. Please never stop making these 🙏🏽

[SomeYoutube-blmy]

I literally started writing my own kernel like 1 month ago as part of my mastery at 42. Would have been way harder to understand what I actually have to do without your videos starting at how stack heap works until now with this video!

Massive respect being able to explain SO complex topics so that they are easy to understand - shows crazy mastery of the subject.
Keep up the amazing work!

[vikaspoddar]

Please do a series on RISC-V based softcore CPU, and it's interaction with kernel code, how ISA and architecture are related and compiler's compilation process

[ItsCOMMANDer_]

Fun fact: in x86, the mmu page tables are in memory, so if the os for whatever reason maps a part of memory where a page table is located, into a proceses virtual memory space, then the proces can modify the memoy layout using usermode instructions.

[soranuareane]

Professional software engineer here. I want to commend you for making this video; the topics are presented accurately, clearly, and with both honesty and integrity. You gloss over the concepts we don't need to understand (such as how interrupts are triggered from a hardware level or how program segments are loaded) and instead focus on only exactly what is needed to convey the topic.

Your definitions of "kernel mode" and "user mode" are perhaps the simplest and most accurate definitions I've heard to date.

Thank you for using an x86-derivative assembly language in your examples. In my experience, it's the easiest to follow for new students who have not had exposure to assembly language programming.

Thank you for discussing what can go wrong when the Mode Bit is mishandled.

[MidoriMizuno]

I absolutely love how you mentioned about kernel mode drivers being potentially untrustworthy (and that you're sceptical about proprietary operating systems too). I think it's very important to help people realise that.

[privatesocialhandle]

Labeling this video as a "bit mode" video is an understatement. I spent hours and got the best books about OS fundamentals and none of them put it all together like this. Even some books dive in more specific details like what is an Interrupt Vector Table etc. None of them puts it all together like this.

You've got a sub.

[therealcandlestickmaker]

As a current electrical engineering student I am very glad I found this channel. Keep up the great work George!

[VideosViraisVirais-dcnx]

Your videos simplify boring textbooks so well, that I'm starting to feel inpired to create videos. Honestly, your Ability to create engaging scripts is beyond the curve. Keep improving 🎉

[richardparker]

I don't care about AI voice. I care his explanation and teaching, which is top notch.

[bodycowlin]

Babe wake up, new Core Dumped video just dropped! 🎉

[person]

This has been quite interesting, I'm doing a project with a friend (for fun). He's writing his own OS, and I'm writing the file system for it. I hadn't really considered how privileged mode is enforced, or how the kernel is able to enter and exit it securely. Thank you for the easy to understand video, it was great!

[o_]

There’s always this ambiguous talk about user space, kernel space and privileges; but it never really clicked for me and I never gained any intuition. This video fills the exact gaps everyone forgets to answer with much detail. Thanks <3

[seid]

what a generational run bro, been here since (almost) the start and praying to stay for long.
i bet this is what it felt like for earlier generations to watch and study from 3b1b and Ben Eater at the time they were releasing their videos.

i've recently started going the book route, going through the computer systems book, and i have to say you are such a good (and even on par) supplement.
i can't wait for the virtual memory video. cheers bro

[halim_Ha]

Damn what a treasure.
I think subscribers should help this channel out give some donation to make sure the sustainability of it.

[desyfer]

To someone like me planning to take OS as my area of specialization (and starting the journey on that path) this is a priceless gem.

[elementare.]

Hugs from Brazil. I simply love your channel. Please keep doing more videos

[__username__]

I haven't been a student for over 20 years now and I understand how processors work in conjunction with operating systems.
But damn, this video is just great. I think it would be great for explaining how protected mode works to non-IT people. Thanks a lot for the work!