1. FatMax 2007. Licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 LicenseCreative Commons Attribution-NonCommercial-ShareAlike 2.5 License 11.4 Software Operating Systems

2. FatMax 2007. Licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 LicenseCreative Commons Attribution-NonCommercial-ShareAlike 2.5 License Operating Systems All desktop computers use an operating system. Common desktop operating systems include: Windows OS X Linux There are hundreds of other operating systems available for special-purpose applications e.g. mobile phones

3. FatMax 2007. Licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 LicenseCreative Commons Attribution-NonCommercial-ShareAlike 2.5 License Functions of an OS Processor management Memory management Device management Storage management Application interface User interface You need to know this for the exam!!!

4. FatMax 2007. Licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 LicenseCreative Commons Attribution-NonCommercial-ShareAlike 2.5 License Processor Management The OS has manage the execution of processes so that you believe that there are several things happening at once. However, the processor can only do one thing at a time. In order to give the appearance of lots of things happening at the same time, the OS has to switch between different processes thousands of times a second making sure that each process and application receives enough of the processor's time to function properly.

5. FatMax 2007. Licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 LicenseCreative Commons Attribution-NonCommercial-ShareAlike 2.5 License Memory Management The OS manages memory (RAM). When applications are loaded they need memory to work with. The OS allocates software RAM to work in. It ensures that the RAM allocated is not used by another application. The OS also manages virtual memory. In this way the computer can run more applications than it has RAM for. For example if a computer was running a word processor and the user wanted to load a spreadsheet application at the same time and there was not enough RAM then the OS uses the hard disc as virtual RAM. Click on the image to watch a short Flash presentation about memory management

6. FatMax 2007. Licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 LicenseCreative Commons Attribution-NonCommercial-ShareAlike 2.5 License Device Management (Input/Output) The OS makes use of queues and buffers, special storage facilities that take a stream of bits (data) from a device, e.g. a keyboard, hold those bits, and then release them to the CPU at a rate slow enough for the CPU to cope with. This function is very important when a number of processes are running and taking up processor time. The OS will instruct a buffer to continue taking input from the device, but to stop sending data to the CPU while the process using the input is suspended. Then, when the process needing input is made active once again, the OS will command the buffer to send data.

7. FatMax 2007. Licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 LicenseCreative Commons Attribution-NonCommercial-ShareAlike 2.5 License Device Management (Drivers) The operating system needs to communicate with the various hardware components which make up the computer. Special programs called drivers enable the OS to communicate with these hardware devices. Drivers are needed as the hardware which makes up a PC may be vastly different to that of another PC with the same OS installed. Drivers are translation programs which convert the messages from the OS into messages that the hardware device can understand.

8. FatMax 2007. Licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 LicenseCreative Commons Attribution-NonCommercial-ShareAlike 2.5 License Application Interface In much the same way that drivers provide a way for applications (software) to make use of hardware without having to know every detail of the hardware's operation, application program interfaces (APIs) let application programmers use functions of the computer and operating system without having to directly keep track of all the details in the CPU's operation. Think of an API as a set of common routines, protocols, and tools for building software applications. A good API makes it easier to develop a program by providing all the building blocks. A programmer puts the blocks together.

9. FatMax 2007. Licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 LicenseCreative Commons Attribution-NonCommercial-ShareAlike 2.5 License User Interface The user interface (UI) brings structure to the interaction between a user and the computer. In desktop computers the user interface is a program or set of programs that sits as a layer above the OS. The core operating-system functions - the management of the computer system - lie in the kernel of the operating system. The display manager is separate, though it may be tied tightly to the kernel beneath. Mac OS X GUI

10. FatMax 2007. Licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 LicenseCreative Commons Attribution-NonCommercial-ShareAlike 2.5 License Exam Stuff A common question on the exam is: Explain four tasks that an operating system carries out in the background Can you answer this question?