Computer System (By Joshua Beard)

Computer System (By Joshua Beard)

1. Managing Resources

   • Managing peripherals such as input and output devices
     • Communication with and sends data to output devices
     • Communicates with and receives data from input devises
   • Manages printing using spooling
     • Data is stored on HDD/on SSD/in memory/stored in a queue
     • Document is printed when printer is free/in correct order
     • Benefits from Spooling - ready for more sheets
   • Manages Backing Storage
     • Ensures data is stored and can be retrieved easily
     • Creates and maintains Filing systems such as FATS or NTFS
     • Organise files in a hierarchical directory structure
   • File Compression
     • Compresses to save disk space
     • The amount of data is reduced and the file is made smaller
   • Disk De-fragmentation
     • Fragmented files are files that are split up and stored in random places
       • The leads to the computer being slow
     • Physically moves and re-arranges files
   • Manages Memory (RAM)
     • Ensures programs and data do not corrupt each other
     • Ensures all programs and data (including itself) is stored in the correct memory locations
   • Manages Processes
     • Ensures that different processes can utilise the CPU and do not interfere with each other (or crash)
     • On a multi-tasking OS (Operating System) ensures that all tasks appear to run simultaneously
   • Manages Security
     • Allows creation and deletion of user accounts
     • Allows users to logon and change passwords

2. Providing User interface

   • Allows access to system settings such as hardware
   • Provides a command line interface
   • Allows users to have more than one window open
   • Allows the user to switch between tasks (programs/windows)
   • Allows customisation of the interface. E.g: Change the desktop background
   • Provides user with errors/help messages
   • Provides a graphical user interface (Windows, Icons, Menus, Pointers)
   • Allows copying/deleting/moving/sorting/searching of files or folders

3. Libaries, software development enviroment

   • Libaries
     • Collection of commonly used private functions and sub-programs
       • Example of a private function: Mathematical operations
       • Example of a sub-program: Standard input and output routines
       • Can be called at any time
     • Advantages
       • Time is saved as the programmer can simply use the private functions and programs stored in a libary
       • Related private functions and subprograms are stored in the same location
       • Subroutines contained in a library have already been tested, so they should work reliably and not need further testing
       • Programs will contain less code and will therefore be easier to maintain
     • Most computer language use standard libraries even though you can make your own custom library
   • Software development environment or Integrated Development Environments (IDE)
     • Tools needed to create a program
       • Editor
         • Allows the 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 every line of source code into machine code and executes it as each line of code is run
           • This is performed each time the program needs to be run
       • Linker
         • Allows previously compiled code, from software libraries, to be linked together
       • Loader
         • Loads previously compiled code into memory
       • Debugger
         • Helps locate, identify and rectify errors in a program
       • Trace
         • 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
         • Interrupts a program on a specific line of code, allowing the programmer to compare the values of variables against expected values
           • This program code can then usually be executed one line at a time (this is called single-stepping)
       • Variable Watch
         • Displays the current value of any variable
           • The value can be 'watched' as the code is single-stepped to see the effects of the code on the variable
             • Alternatively, a watch maybe set which will interrupt the program flow is the watch has reached a specified value
       • Memory inspector
         • 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

4. Disk orginisation

   • Formating
     • Process of preparing a disk for use
       • During process a new file system is set on disk and all data maybe erased in readyness for new data to be stored
   • File transfer
     • The ability to transfer data from one place to another
       • Done simply by coping a file from one folder to another or from one storage medium to another
         • May with to carry out either of these tasks in order to organise your files better, using subfolders or to back-up your work onto a secondary storage device
   • Compressing
     • Process of making a file size smaller
       • Allows more date to be stored on the disk and transferring is quicker and easier
       • Two methods to compress:
         • Software based
           • In most operating systems
             • Downside is that is slows down the process of reading and writing to disk
         • Hardware based
           • Requires specialist hardware (which is expensive)
             • Does not affect the speed of access as much as software based disk compression