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After that fun review of the power of abstractions, next we will take a look at the hardware resources being managed by the operating system.

Hardware Continuum

As we will see, one of the operating system's role is to control access of the applications to physical hardware. So a basic understanding of hardware components and how they interact is essential to the course. Let's do a quick review. What better way to start the review than by a fun quiz. Now in this quiz, I'm showing you the hardware continuum that exists today in terms of the devices that you and I are using on an everyday basis. Smartphones all the way to the cloud and a lot of data points inbetween. There are tablets, and laptops. There are desktop computers. There are servers. And of course, the cloud computing itself that you may have heard of, that is being enabled by data centers. So this is a hardware continuum that you're looking at. And the question that I'm posing to you is, is the internal organization of computer system in this continuum, going all the way from smartphone to the cloud. Is this vastly different? That's the question. And it's a binary answer. Yes or no.

Hardware Continuum

The right answer is no, and since this might seem a bit counterintuitive given this huge range of the hardware continuum, let's reason it out. Basically, the hardware inside a computer system consists of the processor, memory. And implode the devices. And the organization of these hardware elements within the computer system, whether we are talking about smart phone or cloud, is not going to change tremendously.

Hardware Resources in a Computer System

So we have this hardware continuum from cell phones and PDAs to laptops, to tablets, to desktop computers, all the way to nodes in a data center that is providing cloud computing services. Regardless of these different manifestations and sizes, the organization of the hardware inside the computer system is pretty much the same. You've got a CPU. And the CPU is connected to a conduit, which we call the bus. And you've got memory that has the instructions and data that is needed for the CPU to execute. And the CPU can use it's conduit, namely the bus, to access the memory. And you need storage for persistance of files and other data that your produce during the computation. And, once again the CPU can access stuff on the student's device through a controller that is also connected to this conduit. And you may have other peripheral devices, like a microphone and a camera. All of these devices, of course, are accessible for the CPU through this conduit, which is the bus. And of course in this day, and age a device has to be able to communicate with the outside world. You have a network, and once again the network is interfaced through a controller to the CPU via this conduit. So this conduit for communication Which is the BUS, serves the purpose of connecting the CPU to the memory as well as all the iode devices that it may need to interact with in order to do whatever the intent is of the user and the application that they want to run on the computer. And depending on the sophistication of the device that we're talking about, and the speed of the device that we're talking about. These controllers that I'm showing you may have different capabilities. So for instance a network controller may have the ability to move the data directly from the memory into the network, or from the network into the memory and this As you may have learned in a computer organization course, is called direct memory access for the controller to move data swiftly between memory and the IO device. And similar DMA facility may exist in the controllers of other high speed devices, this is the high speed device. So that's the capability that you got for some of these controllers. Some of these controllers may be slow enough, for instance a keyboard or a mouse, that the CPU can directly query new data that is coming from the controller that is associated with slow speed devices, and move it into memory or use it in any fashion that it wants.

Organization With I O Bus

Here are the more elaborate organization of the hardware resources inside a computer system with an I/O Bus and a system Bus, and usually the system Bus, is a synchronous communication device between the CPU and the memory. The I/O bus is primarily intended for the devices to communicate with the CPU. And the intent is that the individual needs of each of these devices, in terms of the communication bandwidth that they may need, is less than the cumulative bandwidth that may be available for the CPU to communicate with the memory. Or in other words, the system bus has a communication bandwidth that is much more than the communication bandwidth that's available in the I/O bus. So the system bus is a high speed bus and it connects via a bridge to the I/O bus. And this bridge itself, could be a specialized IO processor for scheduling the devices that need to communicate with the memory for instance, if it is a DMA device or need to communicate with the CPU if it's a slow speed device. So the role of the bridge is like a processor in itself. Controlling who has access to this I/O bus among the set of devices that maybe competing at the same time for attention by the CPU and communicating the intent of these I/O devices either directly with the memory or via the CPU. The I/O bus is typically lower speed than the higher speed system bus. And the cumulative bandwidth that is needed in the system bus is usually much higher because it has to cater to all the clients that may want to access the memory, either from the CPU or from any of these devices coming through this bridge. There may be other high-speed devices, for example, a frame buffer, of a graphics display that may also be hanging off of the system bus due to the need for refreshing the screen in a rapid manner from the memory. So in a nut shell, if you look at the internal organization of a computer system that are going to be one or more CPUs, whether it is a single-core machine or multi-core machine or parallel machine and so on. You're going to have one or more CPUs and youre going to have a bunch of memory that the CPUs can access and there's going to be a whole number of input-output devices. And device controllers that allow these devices to communicate with the CPU, or directly with the memory. And there are conduits, system bus and I/O bus, for connecting these controllers to the CPU as well as to the memory. Basically, these conduits allow ferrying data from the CPU to the devices, or from the devices to the CPU, and between CPU and the memory, as well as from the devices to the memory. This is why I mentioned earlier that there is no difference in the organization, regardless of the platform specifics, the form factor may be different, or the intended use may be different of a particular platform. But the internal organization is pretty much going to look as I've shown you here in terms of the hardware elements that are going to be there as well as the connectivity that you might see among these hardware elements.

The Specifics

The specifics, such as the computational power, the memory capacity, and the number and types of input, output of devices, may vary from one manifestation of a computer system, to the next. For example, commensurate with it's intended use, a cell phone or a pda may have very limited input/output capabilities such as a graphics display, speakers and microphones. But on the other hand, a high end supercomputer used for running large scale scientific applications may employ thousands of CPUs, incorporate several terabytes of memory and be connected an array of disks with storage capacities on the order of several parabytes.


In summary then, the organization of a computer system is consistent enough that many of the key operating system concepts apply to all of them regardless of size and capacity. On the other hand, these differences should not be ignored and advances in hardware have helped drive innovation in operating systems, so that we can get the most out of their capabilities.