[5] System Software

• Benefits of using program libraries (3)

  · saves programming/testing time as code not need to be written/test

  · code already tested – more likely to work

  · if improvement to library routine it automatically updates

  · perform complex calculations that programmer unable to do
• Management tasks by OS

  · memory

  · file

  · security

  · hardware

  · process
• Memory Management tasks

  · control movement of data between RAM processor VM

  · allocates memory to processes
• File Management

  · creates files/folders

  · renames
• Security Management tasks

  · creates accounts/ passwords

  · provide firewall/anti-malware
• Process management

  · decides which process to run next

  · supports multitasking
• Back up software

  · make copy of data at regular intervals

  · if lost/corrupted it can be retrieved
• Defragmentation software

  · move free space together

  · individual files contiguous blocks · improve disk access time
• Utility software types:

  · disk formatter

  · virus checker

  · defragmentation software

  · disk contents analysis/disk repair software

  · file compression

  · back-up software
• Virus checker

  · scans for virus

  · makes RAM more available

  · removes software taking up memory/replicating
• How program library used

  · stores pre-written functions/routines

  · library referenced/imported

  · functions can be called
• Disk formatter

  · initialises disk

  · sets up disk ready to store files

  · deletes existing data
• Disk repair

  · scans for errors + fixes

  · optimises space
• Why need OS

  · Hardware unusable without OS

  · Acts as interface between user and hardware

  · Provides software for other programs to run on
• DLL file

  · Dynamic link library

  · Shared library file

  · Code saved separately from main file

  · Code loaded in only when required

  · Made available to several applications same time
• Operations of compiler

  · Attempts to translate whole source code

  · Creates error report at end of translation

  · If translation successful/no errors then executable file
• Operations of interpreter

  · Reads each line translates it then executes it

  · Stops when error occured
• Context sensitive prompts

  Displays predictions of code being entered
• Dynamic syntax check

  • underlines/highlights statements that do not meet rules of language
• Single stepping

  executes one line of program and then stops
• Report window

  output contents of variables + data structures
• Breakpoint

  stops code executing at a set line
• Make use of IDE for writing code

  · Context sensitive prompts

  · Pretty printing

  · Expand/collapse blocks

  · Auto format/index

  · Dynamic syntax check
• Make use of IDE for testing code

  · Single stepping – execute line by line

  · Breakpoints – check values at certain point

  · Report window – see how variable change
• PrettyPrinting

  identify key terms (structure/variable name)
• Assembler

  The software translates low-level statements into machine code for the processor to execute.
• what to use High level –> machine code

  Compiler/interpreter
• Low level –> machine code

  Assembler
• Differences between compiler + interpreter

  · Compiler executable file unlike interpreter

  · Compiled program distributed independently

  · Compiler produces error at end. Interpreter line by line

  · Interpreter executes each statement immediately compiler checks whole program

  · Source code present required for interpreter
• Benefits of compiler

  · Once translated compiler not needed to run

  · Execute faster

  · Produce executable file

  · Executable file distributed keeping source code protected
• Benefits of interpreter

  · Easier to debug

  · Stops when error encountered

  · Error corrected real time

  · Translates statement + executes immediately

  · Part of program tested without all program code available