Computer System

Computer System

1. Managing resources and providing user interface

   • An operating system is software that manages a computer system. The operating system is loaded by the bootstrap loader. One of its primary functions is to manage resources.
     • Manages peripherals such as input and output devices
       • • Communicates with and receives data input to a keyboard/mouse/other valid input device
       • • Communicates with and sends data output to a printer/monitor/other valid output device
     • Manages printing using spooling
       • • Document is printed when printer is free/in correct order
     • Manages backing store
       • • Ensures that data is stored and can be retrieved correctly from any disk drive
     • Disk de-fragmentation
       • • Disk fragmentation will slow down disk access speed
       • Fragmented files are split up and stored on different parts of the disk
     • Manages memory (RAM)
       • • Ensures that programs/data do not corrupt each other
       • • Ensures that all programs and data including itself is stored in correct memory locations
     • Manages processes
       • • Ensures that different processes can utilise the CPU and do not interfere with each other or crash
     • Manages security
       • • Allows creation and deletion of user accounts
       • • Allows users to logon and change passwords

2. Libraries, software development environment

   • A library is a collection of commonly used private functions and subprograms. Examples of private functions include standard mathematical operations such as square root, random number generators. Examples of subprograms include standard input/output routines, such as saving data to disk. These functions and subprograms can be called from within your program anytime, but only when the appropriate library has been linked.
     • The advantages of using standard libraries are that
       • • related private functions and subprograms are stored in the same location • time is saved as the programmer can simply use the private functions and programs stored in a library
       • • programs will contain less code and will therefore be easier to maintain
       • • subroutines contained in a library have already been tested, so they should work reliably and not need further testing
     • Software development environment
       • Software development environments, also known as Integrated Development Environments (IDE), provide programmers with various tools that are needed to create computer programs. Here are some of the tools and facilities offered by software development environments:
         • Editor Allows a programmer to enter, format and edit source code
           • Compiler Converts source code into executable machine code. Once compiled, a program can be run at any time
             • Interpreter Converts each line of source code into machine code, and executes it as each line of code is run. The conversion process is performed each time the program needs to be run
               • Linker A program which allows previously compiled code, from software libraries, to be linked together
                 • Loader A program which loads previously compiled code into memory
                   • Debugger A program which helps locate, identify and rectify errors in a program
                     • Trace A facility which displays the order in which the lines of a program are executed, and possibly the values of variables as the program is being run
                       • Break point A facility which interrupts a program on a specific line of code, allowing the programmer to compare the values of variables against expected values. The program code can then usually be executed one line at a time. This is called single-stepping
                         • Variable watch A facility which displays the current value of any variable. The value can be 'watched' as the program code is single-stepped to see the effects of the code on the variable. Alternatively a variable watch may be set, which will interrupt the program flow if the watched variable reaches a specified value
                     • Memory inspector A facility which will display the contents of a section of memory
                       • Error diagnostics Used when a program fails to compile or to run. Error messages are displayed to help the programmer diagnose what has gone wrong
     • Disk defragmentation; Files are stored on computer systems that can, over time, become fragmented. This means that they are split and stored on different parts of the disk. If a file is fragmented, it takes longer for the disk heads to move between parts of the file, which slows the process of loading it. Defragmentation is the process where files are physically re-arranged on disk so that they are no longer fragmented and the parts of each file are stored together. This improves the speed of accessing data from disk.
       • Virus protection; A virus is a computer program that is able to copy itself onto other programs often with the intention of maliciously damaging data. The consequences of a virus spreading can have catastrophic effects on computer systems, and therefore need to be prevented. Virus protection software, also called anti-virus software, is a program that can be loaded into memory when the computer is running. It monitors activity on a computer system for the signs of virus infection. Each virus has its own unique ‘signature’ which is known to virus protection software and stored in a database. Data stored on a computer system is scanned to see if any of the virus signatures within the database exist on the system. There are many thousands of known viruses, and new viruses are created daily. Virus protection software therefore needs to be updated regularly to combat these.
         • Firewall A firewall can be a software or hardware security system that controls the incoming and outgoing network traffic. Packets of data are analysed to determine whether they should be allowed through or not.
     • Control panel Many operating systems use a control panel to give the user control of software and hardware features. It enables the user to change settings, such as sound, device and display settings all from one convenient location.

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