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OS Functions
1. Topic 5 - Software Computer hardware would be useless without software , the lists of instructions which tell the hardware what to do. Computers require various types of software to make them useful. These can be classified as follows: 1. Operating System 3. Applications software 2. Utility software
2. Operating System The operating system(OS) is the piece of software required by the computer to make sure that it works correctly and efficiently. It manages the computer and allows the user to communicate with the hardware . Storing the OS on disk means that it can be easily updated . Windows Vista and XP are updated on a daily basis. Modern operating systems are typically stored on Hard disk and loaded into RAM when the computer is switched on. 1. Operating system 3. Applications software 2. Utility software
3. The bootstrap loader The bootstrap loader is a small but very important part of the OS which is permanently stored in ROM . When the computer is first switched on the bootstrap loader starts to run. It checks the RAM and input/output devices to make sure that they are working and then locates the OS on backing storage , usually on Hard disk but could be on CD or even a memory stick. It then loads the OS into RAM and the OS takes over control. 1. Operating system 3. Applications software 2. Utility software
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15. Utility Software Utility software consists of programs which are designed to help with the maintenance of the computer and to ensure sure that it works correctly and efficiently. The distinction between utility software and functions of the operating system is rather blurred as modern operating systems are often bundled with utility software . e.g. disk defragmenter, anti-spyware tools, firewall. 1. Operating system 3. Applications software 2. Utility software
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26. A virus is a program or programming code that replicates itself into another program or document. Virus, Worm & Trojan Horse Are viruses, worms and trojan horses all the same? A virus cannot be spread without a human action , (such as running an infected program) to keep it going. NO
27. A worm does not alter files but resides in active memory and replicates. Worms use parts of an operating system that are automatic and usually invisible to the user. Virus, Worm & Trojan Horse Are viruses, worms and trojan horses all the same? Worms spread from computer to computer and, unlike a virus, have the ability to travel without any help from a person NO
28. Due to the copying nature of a worm and its ability to travel across networks the end result in most cases is that the worm consumes too much system memory (or network bandwidth). Virus, Worm & Trojan Horse Are viruses, worms and trojan horses all the same? NO This causes Web servers , network servers, and individual computers to stop responding and networks grind to a halt.
29. At first glance they will appear to be useful software but will actually do damage once installed or run on your computer. Virus, Worm & Trojan Horse Are viruses, worms and trojan horses all the same? NO Trojan horses do not reproduce by infecting other files nor do they self-replicate . The user is tricked into opening them because they appear to be receiving legitimate software or files from a legitimate source.
30. Some Trojans are designed to be more annoying than malicious (like changing your desktop, adding silly active desktop icons) or they can cause serious damage by deleting files and destroying information on your system. Trojans can also create a backdoor on your computer that gives malicious users access to your system, allowing confidential or personal information to be compromised. Virus, Worm & Trojan Horse Are viruses, worms and trojan horses all the same? NO
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36. There are many standard file formats for graphic files. Each has its own advantages and disadvantages and users should choose formats carefully depending on the purpose for the graphic file. Graphics file formats Compression Graphics files, particularly bit-mapped graphics, can generate very large file sizes . It is possible to analyse the data in the file and cut down on the data which needs to be stored . This is known as compression .
37. Lossless Compression Graphics file formats This technique manages to cut down on the amount of data which needs to be stored but does not actually lose any of the data . This means that the quality of the image is not affected . Compression saves disk space but affects system performance as saving and loading takes longer due to the extra processing involved. Lossy Compression This technique cuts down on the amount of data which needs to be stored by discarding some of the data . This means that the quality of the image is affected .
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42. When choosing software it is important to examine the system requirements to make sure that the software will run on the hardware. System requirements will typically include details on: Storage Requirements Memory OS compatibility i.e. how much RAM is required for the software. i.e. how much Hard Disk space is required for the software. i.e. which operating system it requires. Software Compatibility
