5.1 Operating systems

Operating systems (management tasks):

• File management

• Memory management

• Device/hardware management

• Process management

• Security management

• Input/output management

• Error checking and recovery

• Provision of a platform for software

• Provision of a user interface

“Describe the purpose of an OS in a computer”

• To provide a user interface

  • So that the user is able to communicate with the hardware

• To manage memory

  • So that data can be stored and accessed

  • And multi-tasking is possible

• To manage files

  • Allowing the user to create, edit, update and delete files and folders

• To manage inputs and outputs from hardware/peripherals

• To handle processes

  • To make sure each process has fair access

“Describe how the Operating System (OS) manages processes in the computer”

• Manages scheduling of processes

• Manages which resources the processes require

  • Such as allocating memory

• Enables processes to share data

• Prevents interference between processes

• Handles the process queue

• Allows multi-tasking

  • By ensuring fair access, handling priorities and handling interrupts

“Describe process management tasks of an operating system” **Short answer

• Decides which processes to run next

• Supports multitasking

“Explain how memory management and process management support multi-tasking”

Memory:

• Stores data from all currently running programs concurrently in RAM

• Stops data from overwriting each other in RAM

• Decides which processes should be in main memory

• Makes efficient use of memory

Process:

• Allows one process to be paused whilst another process can be actioned

• Decides which process is to be run next

• Switches between processes to allow them to share the use of the processor

• Scheduling (example)

“Describe memory management tasks of an operating system” **Short

• Controls the movement of data between RAM, processor, VM etc

• Allocates memory to processes

“Describe the ways in which memory management organizes and allocates Random Access Memory (RAM)

• RAM is assigned into blocks

• Dynamic allocation of RAM to programs

• Reclaims unused blocks of RAM

• Prevents two programs/processes from occupying the same area of RAM at the same time

• Moves data from secondary storage when needed (manages paging, segmentation…)

Operating system (Security management)

• Prevents unauthorised access

  • by providing authentication

• Implements access rights and permissions

• Makes provision for recovery of lost data

• Carries out operating system security updates as available

• Carries out auditing and keeps logs of activity

“Describe the file management tasks that an Operating System performs”

• Secondary storage space is divided into file allocation units

• Space on secondary storage is allocated to particular files

• Maintains/creates directory structures

• Specifies the logical method of file storage (FATS or NFTS)

• Provides file naming conventions

• Controls access to the file by other software//implements access rights

• Controls user access

• Specifies tasks that can be performed on a file e.g. close, delete, copy, create, move etc

• Allows searching for a file

“Describe file management tasks of an operating system” **Short

• Creates files/folders

• Renames files/folders

“Describe hardware management tasks of an operating system” **Short

• Receives data from input devices // sends data to output devices

• Use of device drivers

“Describe how the Operating system manages the peripheral hardware devices of the computer”

• Installs device drivers

  • To allow communication between peripherals and computers

• Sends data and receives data to and from peripherals

  • Such as to an output device and from an input device

• Handles buffers for transfer of data

  • To ensure smooth transfer between devices that transmit and receive at different speeds

• Manages interrupts/signals from the device

“Disk formatter short function”

• Sets up disk so it is ready to store files

“Defragmentation short function”

• Moves parts of files so that each file is contiguous in memory

“Back-up short function”

• Creates a copy of data in case the original is lost

“Disk repair short function”

• Scans for errors in a disk and corrects them

“Virus checker short function”

• To scan for malicious program code

“How does defragmentation improve the performance of a computer”

• Less time is taken to access files because each one is contiguous so there is less head movement

“How does a virus checker improve the performance of a computer”

• Makes more RAM available for programs to run

  • Because it removes software that might be taking up memory/replicating

“How does disk-repair improve the performance of a computer”

• Preventing bad sectors being used because it marks them

• Reduces access times by optimising storage

“How does disk clean up improve the performance of a computer”

• Releases storage by removing unwanted/temporary files

“How does defragmentation improve the performance of a computer”

• Rearranges blocks of individual files (on the HDD) so they are contiguous

• Accessing each file is faster

  • Because there is no need to search for the next fragment / block of the file

  • So less head movement is needed

“Describe the purpose of back-up software”

• To make a copy of data at regular intervals

• So that if it is lost/corrupted, it can be retrieved

“Describe the purpose of defragmentation software”

• Make individual files occupy contiguous blocks // move free space together

• Improve disk access times // data files can be loaded faster

“Examples of utility software”

• Compression software

• Disk formatter

• Virus checker 

• Disk analysis software

• Disk repair software

“Describe the purpose of utility software in a computer”

• To help users set-up/optimise/maintain the computer

  • Eg. making memory allocation more efficient

  • Eg. checking the system for faults

“Explain the need for back-up software”

• To allow data to be retrieved/restored when lost

• To automatically make a duplicate copy of data

  • So the user does not have to remember to backup data

• To make regular duplicate copies of data

“How a program library can be used while writing a computer program”

• Program libraries store pre-written functions and routines

• The program library can be referenced

• The functions can be called in their program

“Two benefits to a programmer of using Dynamic Link Library”

• Memory requirements for program are reduced as dynamic link library is loaded only once

• The executable file size is smaller because the executable does not contain all the library routines

• Maintenance not needed to be done by the programmer because the DLL is separate from the program

• No need to recompile the main program when changes are made to DLL because changes to the DLL file code are done independently of the main program

“State what is meant by a program library”

• Pre-written code that can be imported in another program

“Describe the benefits of a programmer using a library with DLL files instead of using a library that does not include DLL files”

• Maintenance not needed to be done by the programmer

  • DLL is separate from program

• The calling program does not need recompilation by the programmer when a DLL file changes

  • Because the DLL file can be updated independently of the calling program

  • Updates will apply to all programs that use the DLL file

“Explain the benefits of using library files when writing a program”

• Saves development time for the student

  • By using pre-written code

• There is less testing to do

  • Because they have already been tested and are error-free

• It results in a more robust program

• Subroutines can be used that they do not have the skill to write

  • Which enables a more complex program to be written

“Describe the benefits to the programmers of creating a program library”

• Subroutines can be shared/reused

  • Between team members who are working independent

  • Without having to rewrite/re-test them which saves the programmers’ time

• A program library provides continuity between programmers

• Individual programmers can contribute their specialisms to the library

“Explain how a programmer benefits from using program libraries during program development”

• Programming time is saved as code does not have to be written from scratch

• Testing time is saved as code is already tested

• A library routine is more likely to work, as code is already tested

• Library routines automatically update is they are changed

• The programmer can use library routines to perform complex functions that they may not have been able to write themselves