2.1 systems software

• An operating system is an essential piece of software that is loaded when a computer boots up.
• • An operating system (OS) is a piece of system software which controls the hardware within a computer.
• • Operating systems provide an application programming interface (API).
  • This is a set of code libraries that software developers can use to write applications for that operating system.
• • The operating system is responsible for many pieces of hardware, each of which is controlled by a dedicated 'manager':
  • The user interface (UI) manager provides the user interface which allows users to control the computer.
  • The device manager allocates resources to external hardware devices and allows them to be used by applications.
  • The memory manager controls the allocation of memory between applications.
• • The user manager authenticates and separates users of the computer.
  • The process manager controls the allocation of central processing unit (CPU) cycles to multiple running applications.
  • The file manager controls the opening, reading and writing of files in secondary storage.
• An application programming interface (API) is a set of code libraries
• An operating system is a piece of system software which controls the hardware within a computer.
• Purpose of memory manager:

  • The memory manager controls the allocation of random access memory (RAM) to each running process.
  • If the memory manager fails to manage memory well, then the computer will slow down and might crash.
• Purpose of process manager:

  • Modern operating systems allow users to run multiple programs at once.
  • In reality, a CPU can only execute one process at a time. So the CPU must switch between processes so quickly that it seems that they are running simultaneously.
• Multitasking:

  • Modern operating systems allow multiple applications to run at once. This is known as multitasking.
  • For this to work, the operating system must manage how memory and CPU time is allocated to each running process.
• The process manager is responsible for central processing unit allocation and multitasking
• The memory manager controls the allocation of random access memory to each running process.
• Operating systems are responsible for managing memory for the user. Managing memory can be done by paging or by segmentation.
• Paging:

  • Paging splits the main memory (RAM) into 4 kb sections known as pages.
  • When programs run they are allocated a set number of pages to run in.
  • Programs can be split across lots of pages that are non-contiguous (not all together).
  • This is managed by a table map.
• Performance: (paging)

  • Performance is not affected by having non-contiguous pages for your program.
  • Any pages being used that are not active can be sent to virtual memory to free pages up for other tasks.
  • Performance may be affected if some programs are split (e.g. when parts of a looping function are split across pages)
• Pages being used that are not active can be sent to virtual memory to free pages up for other tasks.
• Segmentation:

  • There is no physical split in segmentation like in paging.
  • Each program is given a logical division of memory to operate in.
• Segmentation process:

  • When a program loads, it is given enough memory for the parts it is currently trying to load.
  • The rest of the program is kept in storage until needed, but the logical section given to the program will need to be made bigger.
  • Programs that are split across logical splits (non-contiguous) suffer greatly for not being together.
• Virtual memory: (segmentation)

  • Segmentation can also use virtual memory to store unused parts of programs in virtual memory to free space for something else.
• logical division of memory is used in segmentation
• In paging, programs are split across lots of pages that are non-contiguous.