1.2.1 Systems Software

• A piece of software held in permanent storage that controls the software and hardware of the computer • Acts as a bridge between the user and computer’s hardware as the user cannot communicate with the hardware directly

• Provides the interface between the user and the hardware • Provides a platform in which users can run programs

• Some are built into the OS that help maintain the computer • Encryption, Compression and Defragmentation software

• When you more than one program opened and running at the same time • Processor allocates a small amount of time to each process and cycles between them

• Data is stored in files and the extension of the filename tells the OS which application to load the file into • Allows user to rename, delete, copy and move files • Client-server network may impose a fixed/roaming profile and manage login requests to the network

• Allows users to log onto the same computer • OS retains settings for each user as each user may have different access rights to files and programs

• WIMP • Visual • Intuitive • Optimised for touch and mouse gesture input

• Where memory is split into equal sized sections (pages) • Physical divisions in which programs are split up to fit in a given number of pages

• Allows memory to be allocated in a non-contiguous manner - pages of the same process don’t need to be stored together but can be allocated whenever there’s free space in memory

• Inefficient: could separate instructions inside a looping condition and are in different pages

• Memory is spit into logical sized divisions known as segments, which are complete sections of programs and vary in size

• Segments do not need to be stored continuously across a fixed address space • Can be moved in and out of memory as required

• Both allow programs to run despite insufficient memory • Stored on disk • Both pages and segments are transferred into RAM when needed

• Pages are fixed size, Segments vary in size • Pages are made to fit sections of memory, segments are complete sections of programs • Pages are physical divisions, segments are logical divisions

• An allocated area of a hardware/secondary storage device which is used when there’s not enough physical RAM to store open programs

• Extends memory available: swapping instructions and data out of RAM into secondary storage means a vast quantity of memory is potentially available

• Accessing a secondary storage medium is slower than accessing RAM, may slow down performance • Disk thrashing: When the computer ‘freezes’ due to pages/segments being swapped out too frequently between the hard disk and RAM

• A way of signaling the processor when other devices and applications require attention

Program with a set of instructions that need to be fetched, decoded and executed in order to carry out the operations of the interrupt

Built into the OS or provided via device drivers

• Hardware device has signaled it has data to be processed • Hardware failure has occurred and needs to be addressed • Software process needs a service to be provided/ OS function needs to be performed

Yes, interrupts always have a higher priority than normal programs

• Power supply failure • Power/reset button pressed

• Keyboard presses • Tapping an icon to load a new program