1.2 Software and software development

• immediate addressing

  value in address/operand is the actual value to be used
• Direct Addressing

  Value in address/operand is a reference to address in memory where value is located
• Indirect Addressing

  Value in address is a reference to a memory location that contains the address in memory where the value is located
• Shortest Job First

  makes use of a queue
• File Managers

  allows directories, folders and files to be created, copied, moved, deleted and renamed
• BIOS

  Basic input output system

  Software that is stored in non-volatile memory that carries out checks on core system components
• Distributed OS

  A model where distributed applications can run on multiple computers linked by communications
• Embedded OS

  Highly specialised and limited operating system for embedded systems
• Difference between paging and segmentation

  paging is fixed size, segmentation is variable size
• How can virtual memory allow a user to run programs when physical memory is full?

  Currently unneeded pages can moved from memory to secondary storage to create room in memory and are moved back to memory when required
• Benefits of memory management

  Security- does not let programs access memory reserved for other programs

  Multitasking- allows multiple programs to run at once
• indexed addressing

  operand holds an address which is offset using the Index Register to find the actual address of the data to be used
• Why use immediate addressing?

  allows simple access to data with no fetch required
• Why use direct addressing?

  allows data to be fetched from memory
• Why use indirect addressing?

  allows a larger range of addresses to be accessed as address fetched
• Why use indexed addressing?

  allows the Index register to be manipulated to access data stored sequentially