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If you walk up to typical computer today, you're likely to find several applications open. One for listening to music. One for playing your video game. A web browser displaying information on some ancient culture from some remote corner of the world. And a messaging application for connecting with friends, and so on. How is it possible for a single device to do all these things, and moreover, do them all at the same time? How can all these diverse applications, written by different programmers who don't even know each other, coordinate? Who's in charge here? The answer of course is the operating system. Hello and welcome to CS6210 Advanced Operating Systems. My name is Kishore Ramachandran and I'll be taking you on a journey to understand the role played by the operating system in providing the rich user experience afforded to modern applications, the modern computers. And along the way, I'll highlight the symbiotic relationship between hardware and software that makes it possible for the computer and the operating system to provide the rich user experience to please you. Operating systems have evolved over time. In this course we will see all the advances that have been made in the operating system that has led to the state of the art in operating systems today. Covering a variety of platforms, from cell phones to multi-core, to parallel systems, to distributive computing and cloud computing. In part one of this introductory lesson, my goal is to primarily talk about the power of abstraction. That will lay the foundation for the rest of the introductory lesson, which will include an overview of the hardware resources managed by the operating system. The operating system functionality that is expected, and the abstractions in an operating system for managing the hardware resources. By the end of the lesson, we will be ready to discuss the structure of operating systems.

Background Material

Much of the background that you'll need to know, is covered in this introductory lesson and the review lessons taught by Charlie Brubaker. However, to get the full benefit of this course, you should have a strong undergraduate background in computer systems and networks. With that in mind, let's get started with our review and load some of the operating systems basics into our collective memories. I've intentionally structured this lesson to be quiz-heavy, since most of the background material should be already familiar to you. And hopefully that format that I'm going to use, we'll find this to be a more fun way to jog our collective memories.

Which is an OS

Having promised you that, let's start with a quiz. Now this quiz is a fun quiz just to get you primed. Which of the following is an operating system? I'm sure that you've been using a lot of these things and heard these terminologies. Firefox? MacOS? Android? Which of the following is an operating system?

Which is an OS

The names are a gagetary, doesn't it? Well, we all use Firefox. It is a browser. A browser is not an operating system. It is an application that sits on the operating system. You may have heard of Android. It's a system software stack that provides a lot of services but sits on top of the operating system. So in this. Set of choices that I've given you MacOS is really the only one that can be categorized as an operating system.

The Hierarchy

[BLANK_AUDIO] As computer scientists, one of the most powerful tools that's available to us, is the concept of an abstraction. And by an abstraction, we mean a well understood interface, that hides all the details within a subsystem. Let's see how, in a computer system, the hierarchy of abstractions works, and where operating system fits, within this hierarchy.

Which is Not an Abstraction

Again, I'll want to use a fun quiz to get you situated with respect to the concept of an abstraction. Now remember what I told you about an abstraction, that it's an interface that allows us to hide all the details. With that in mind, what I want you to do Is to think about the objects and the terms that I've laid out on this panel for you. And you may have come across many of them and from this set tell me which of these is not an abstraction. There may be more than one item in this set that I've shown you on this panel that may not be an abstraction and I want you to identify all of the items that you think is not an abstraction. The first choice I have is a door knob. The second choice I have for you is instruction set architecture. The third choice I have is the number of pins coming out of a chip, like a processor chip. And the next choice I have for you is a logic gate such as and gate that does the and function. And the next item I have for you is a transistor. And the next item I have for you is the INT data type in a programming language like C. And the last item I have for you is exact location of base pads in a baseball field. So these are the choices that I'm giving you and what I want you to do is think about these different items. Which you may have come across for sure in your every day experience, and tell me which one of these does not qualify as an abstraction. And as I've said, there could be more than one that does not qualify as an abstraction.

Which is Not an Abstraction

Let's walk through all the choices I gave you, and try to understand which can be categorized as an abstraction, and which is not an abstraction. Door knob is something that we use all the time to enter a room, when you open a door. And that's an abstraction because we don't know how the door knob may actually be implemented, nor do we care. So that's an abstraction. Instruction set architecture of a processor is once again an abstraction, because it tells you what the processor's capable of doing, not how it is doing it. Now the third choice I'm giving you here, is the number of pins coming out of a chip. Now, this is being very specific as to, what exactly is going on here? That these are exactly the number of pins coming out of a chip, and therefore it's not an abstraction. The next choice is an and logic gate, again here it's only saying what the function of the logic gate is, not how it is doing it. And therefore, this is an abstraction. The next choice is transistor, and this again, is an abstraction, because we don't know how exactly the transistor is implemented. All we know is a functionality of the transistor. For instance, if a transistor is used as a switching device, you know that using the transistor you can turn it on and off, but you don't know what exactly is going on under the covers in order to make that work in the solid state physics. The next choice is INT data type. Now, again it's only saying that it is a data type and the name is INT. And therefore you can use this as a data type that holds integers in your program, but it doesn't tell you how the data type is actually implemented by the compiler and therefore INT datatype is also an abstraction. The last choice is saying the exact location of base pads in baseball field. Again, this one is being very specific about some particular feature, namely, base pads and how they're laid out in a baseball field and therefore, this is not an abstraction.

Digging Deeper Into the Power of Abstractions

Now, let's dig a little deeper into the power of abstraction as it applies to computer systems. Now, here I'm showing you a screenshot of the Google Earth application. Deep down in the silicon, you have electrons and holes. You may have heard about these terminologies or worked with them in a physics 101 course at some point of time. Let's say that in an application such as Google Earth, you move your mouse from Atlanta, Georgia to Chennai, India. When you do that, magic happens on the screen. Now, between a user action, such as moving the mouse from Atlanta, Georgia to Chennai, India, and the solid state electronics that is enshrined in your computer system, there is a whole series of abstractions.

Name the Abstractions

Now, I want you to help me think about all the abstractions that sit between these two extremes, Google Earth application that makes magic happen on the screen and the solid-state physics the electrons and holes enshrine in your computer system. What are all the abstractions that sit between these two extremes? What I want you to do in this quiz is to name as many abstractions as you can between these two extremes that I am showing you. To make room for you, let me clear some space. I put a box now for your answer. To give you an idea of what is expected in this question, as an answer, let me start you off with naming the abstraction that sits right on top of the electrons and holes. This is of course your solid state physics. And you rain in all the randomness in the movement of the electrons and holes in the solid-state physics, with this abstraction called transistor. The transistor is akin to an on-off switch. Now, what I want you to do is fill the rest of the box with all the other abstractions that sits above transistors, all the way up to the application.

Name the Abstractions

You may have gotten a lot of these abstractions yourself, but let's walk through and think about all the abstractions that sit between the electrons and holes, and applications at the top. We've already talked about the transistor, we know at the lowest level of the hierarchy, the movement of the electrons in the holes. Are governed by the laws of physics. And as I mentioned earlier, transistor reigns in the randomness in the movement of electrons and holes, and gives us an abstraction of a switching device, which is the transistor. Using the switching device which is a transistor, we can implement. The next level up in the hierarchy which are logic gates. Here is where the and- gates and the or-gates and the not-gates come in, where we are implementing Boolean logic using transistor as a switching device. Sequential and combination logic elements are implemented using logic gates such as and, not and or. Logic elements. Sequential and combination logic elements are then organized into a data pack, depending on what hardware circuitry, or functionality we want to implement. The data pack establishes the communication paths we need between these combinational, and sequential logic elements. To realize whatever is the hardware device that we're trying to design, and the control part of it is a finite shaped machine that controls the data path, and implements the repertoire of the hardware device that we are trying to realize. And for instance, if. The intent is to implement a processor, then the instructions in the processor have to be implemented using the data pad, and controlled by the control logic. Next level up in this hierarchy is the instruction set architecture. This is the abstraction that is defined by a processor. When you hear the promo commercial, for instance, that says Intel Inside, it is the ISA, or the Instruction Set Architecture that is being talked about by the promo. Buried within. This term ISA, or the abstraction ISA, is all the details of how the ISA is actually implemented by the data path and the control logic. Now we come to software. Sitting on top of the Instruction Set Architecture, is the system software. Operating systems, compilers, run-time systems and so on, that exercise the instructions provided by the processor architecture. Finally, we have apps on top. This is where applications like Google Earth come in. Notice that the abstraction that is used by the applications themselves is the high level language in which these applications are written. The system software component such as the compiler, translate the high level language used. In writing these applications into the instructions that can be executed on the processor. Similarly, the operating system provides interface for the applications to request services of the operating system. For instance, to access specific devices. During the execution of the application, or for getting resources such as memory. On demand, those are the functions provided by the operating system as an abstraction. Thus, the instruction set is the meeting point between software. And hardware. It serves as the abstraction needed by the system software, for example, the compiler, to generate the code that corresponds to the high-level language constructs that are being used in coding up an application. The software, whether it is. At the system software level or at the application level does not care and does not know how this instruction set may actually be implemented down below. Meaning the implementation of the instruction set itself in terms of data path and control. The sequential logic, elements that sit below that, are the logic gates of the transistor, or finally the electrons and [INAUDIBLE], they don't care what programs are running on top of the processor. So the instruction said architecture is the meeting point between software and hardware. The hardware implementation simply fulfils the contract. Of realizing the instructions of architecture of the processor. Operation system is the abstraction level we will be focusing on in this course, which is a course on advanced operating systems. You will have the opportunity to learn about other levels. In this hierarchy, from other courses that are offered through this program.

Google Earth

Now an application, such as Google Earth, sits at the top of the hierarchy. And it's code for tracking the mouse movement on the screen, written in whatever high level language is compiled into the instruction set and traverses the rest of the hierarchy and magic happens on the screen. Now within this hierarchy, the operating system acts as a broker between the application at the top. And the physical resources such as CPU, memory, and IO devices, can provide an app, with all it needs, for its successful and safe execution.


Most of what we'll be learning in this introductory lesson plan should feel like review to you. If it has been challenging so far, or becomes challenging as you go through the introductory lesson, it might mean that you don't have the necessary background for taking an advanced operating systems course.