The Operating System

Year 12 Lesson

Transcript

1. THE OPERATING SYSTEM COMPUTER SCIENCE
2. Main features
3. Parts of an operating system Kernel This has the task of loading the applications into memory, making sure they do not interfere with one another and allowing them to share use of the CPU efficiently. The kernel also handles file storage to and from secondary storage devices such as hard disks and optical drives. In other words the kernel handles: • Loading / Unloading applications from memory • Scheduling tasks to run on the CPU • Memory management • File management • Data security
4. Parts of an operating system Device drivers Every piece of hardware that makes up the computer or connected to it, will have a device driver that allows the operating system to control and communicate with it. There could be hundreds of device drivers pre-installed with the operating system, and the right ones for that particular computer set-up is loaded on boot-up. The exact detail of which device driver is needed by the operating system is kept in a file - in Windows, the file is called the 'registry' and in Linux the details will be stored as a number of 'configuration files'.
5. Parts of an operating system Device drivers Makers of printers, graphics tablets, scanners, digital cameras and so on, will normally provide device drivers for each make of operating system. A device driver for Windows is different from the device driver for Linux. This is why if you remove an operating system such as Windows from a hard disk, and install Linux instead, you will need to make sure you have all the correct device drivers available for each piece of hardware.
6. Parts of an operating system User interface This part of the operating system is directing what you see on the screen (via the device driver) and reacting to your key presses and other inputs. The user interface could be a basic command line interface, as you might find on a server, or it might be a full blown Graphical User Interface (GUI) such as the Mac OS X, Windows or perhaps Gnome on Linux.
7. Parts of an operating system System utilities This part of the operating system provides all the basic facilities that run in the background without user interaction. For example: • Print spool services • Cryptographic password management. • File management services
8. Single user, single application OS This type of operating system only has to deal with one person at a time, running one user application at a time. An example of a this kind of operating system would be the operating system of a basic mobile phone or an mp3 player. There can only be one user using the device and that person is only using one of its applications at a time. But it still has the same fundamental parts as all the other types of operating system.
9. Single user, multi-tasking You will find this kind of operating system on a personal computer. The operating system is designed mainly with a single user in mind, but it can deal with many applications running at the same time. Example operating systems are: • Windows • Linux • Mac OS The difference compared to the Single-Use, Single Application operating system is that it must now handle running many different applications at the same time. The memory available is also very different, for example it is quite normal to have Gigabytes of RAM available on a personal computer which is what allows so many applications to run.
10. Multi-user, multi-tasking This kind of operating system can be found on Mainframe and Supercomputers. They are highly sophisticated and are designed to handle many people running their programmes on the computer at the same time. Now the operating system has to manage: • Each user logged on to the system, their workspace and so on. • Allocate resources to the jobs they want to run. • Keep logs of how much processing time and resources they use • Work out the most efficient use of computer processing cycles • Maintain security
11. Network operating system These days it is quite common to have your personal computer attached to a network of some kind. For example, most of the computers in school will be networked. Most of the computers in companies will also be networked, and even at home you may have two or more computers networked together so they can share the internet connection. All these machines need to have an operating system that can deal with the network. Examples of a network operating system include Windows Vista, Windows 8 and Mac OS X and of course all the mainframe operating systems. A network operating system has to have the following features: • Deal with users logging on. • Maintain the network connection to the server(s) • Expand the file system to view folders on other computers • Provide security to separate user accounts from each other.
12. Network operating system With a network operating system, you can view folders on other computers, sometimes called 'shares'. They are given a letter, W: perhaps, and as far as you are concerned they are simply an extension of your local hard disk as you can read and write to the folders as if they are on your own machine (as long as the admin has set up your file permissions to at least Read /Write) There may be many users making use of the same machine, so the operating system will create 'user folders' on the local hard disk to store their particular settings and application set-ups (not their files or documents). So when an user logs on to the computer, the operating system will read the settings from the correct username folder and set up the desktop to look just how they last left it along with all the settings or defaults they chose for various applications.
13. Batch operating system A 'batch' is the name given to the task of doing the same job over and over again, the only difference being the input data presented for each iteration of the job and perhaps the output file. This kind of operating system requirement is common on a mainframe computer that was purchased specifically with massive repetitive data processing in mind. For example, a mainframe set up to process 30 million pension statements, each one calculated for a specific customer.
14. Batch operating system A batch job does not need any intervention by a person once the initial commands are set up. Setting up a batch job is a bit like filling out a form, with specific details needing to be provided. Details include:- • Job Owner • Priority of the Job (some jobs are less urgent than others) • How much processor time is allowed for the job (avoids CPU hogging) • Maximum lines to be printed (avoids infinite printouts) • Data file details (for input and output) • What to do if the job fails to run properly (e.g. create a failed jobs report) • Accounting data (to charge the Job Owner for the batch)
15. Real time operating system A real-time operating system is found in systems which aim to control a series of actions by using a computer. For example the engine management computer under the bonnet of the modern car has micro-second control of the engine and exhaust system. It has dozens of rapidly changing inputs such as throttle position, brake pedal position, engine speed and so on. It needs to take all of these inputs, then process them to produce a set of outputs that control the car.
16. Real time operating system Note that 'real time' does not always mean 'fast'. For example, a traffic light computer has a real time operating system that only needs to react within seconds (but react it must!). On the other hand, a safety critical embedded computer as you might find in a braking system would need to react in microseconds.
17. Role of an operating system Resource management 
 
 All operating systems must be able to load programs from backing storage devices, store them in memory and start them running; more complex operating systems have to allocate CPU time, memory and I/O resources to different programs (keyboard / mouse etc.). The kernel of the OS is heavily used here (see note on Kernel below). Usually the most heavily used resource in a computer is the processor. The process of allocating access to the processor and other resources is called scheduling The simplest way an operating system can schedule access to the processor is to allocate each task a time slice.
18. Role of an operating system Backing store management 
 
 Including the creation, updating and deletion of files. Managing the FAT (File Allocation Table) and the directory of files. Hard drive and USB drive management. 
 

19. Role of an operating system i/o control 
 
 Controlling data flow to and from peripherals. 
 

20. Role of an operating system Interrupt handling 
 
 Detecting and servicing interrupts. When a peripheral or software routine requires attention, an interrupt is raised to tell the CPU. Each interrupt has a priority level. If its priority level is higher than the process currently being executed it needs to be serviced first. At the end of the fetch- decode- execution cycle, the processor checks to see if there are any interrupts. 
 

21. Utility software A utility is a relatively small program that has one purpose, usually concerned with maintenance of the system, examples include: • Anti-virus programs • Disc Defragmentation • Compression • File Managers • Backup utilities