System Software

-Moving frequently accessed instructions to cache …for faster recall … as SRAM is used rather than DRAM for cache. -Making use of virtual memory …with paging or segmentation …to swap memory to and from disk. -Partition memory … dividing main memory into static partitions … to allow more than one task to be available -Removing unused item/tasks from RAM … by marking a partition as available … as soon as the process using it has terminated.

-Disk cache … a disk cache holds data that is frequently transferred to/from the disk … the cache can be held in disk or RAM. -Compression utility …decreasing the size of file stored on the disk … in order to fit larger files on the disk -Defragmentation utility … files are rearranged to occupy contiguous disk space … this reduces the time taken to access files/decreases latency.

-Scheduling …better utilisation of CPU time and resources.

-IO operation initiated by the computer user. -IO operation which occurs while software is being run and resources such as printers and disk drivers are requested. - A DMA (Direct memory access) controller is needed to allow hardware to access the main memory independently of the CPU. -DMA initiates the data transfer -CPU carries out other tasks while data transfer operation takes place. -Once the data transfer is complete, an interrupt signal is sent from the DMA to CPU.

-Using graphical interface rather than command line interface. -Using device drivers simplifies the complexity of the hardware interface. -Simplifying the saving and retrieving of data from memory and storage devices. -Carrying out background utilities, such as a virus scanner which the user can “leave it to its own device”.

The written code.

A program that has started to be executed (dynamic).

A data structure which contains all of the data needed for a process to run; this can be created in memory when data needs to be received during execution time.

-Current process state -Process privileges -Register values -Process priority and any scheduling information. -The amount of CPU time the process will need to complete. -A process ID which allows it to be uniquely identified. -I/O status information.

Allow computers to carry out more than one task at a time. Each of these processes will share common hardware resources. To ensure multitasking operates correctly, scheduling is used to decide which process is carried out first.

Process is being created.

-The process is not being executed. -The process is in the queue … waiting for the processor’s attention/CPU time.

-The process is waiting for an event. -So it can’t be executed by the moment. -e.g. Input/Output

-Process is being executed by the CPU. -Process is currently using its allocated time slice.

-Process has finished executing

-Current process is no longer running// processor is available. -Process was at the head of the queue.

-The only required resource become available// resource/event/IO operation is complete.

-When a process is executing it is allocated a time slice. -When the time slice is completed, the process can no longer use the processor even if it is capable of further processing.

-Process is executed when it needs to perform IO operation. -Placed in a blocked state until the IO operation is complete.

1. -Running process is halted. -Process moved to a blocked state 2. -Running process is halted. -Process moves to ready state … until the next time slice is allocated.

-When IO operation is completed for the process in a blocked state. -Process put into the ready queue. -OS determines which process get next use of the processor from the ready queue.

-To be in a blocked state, the process must initiate some IO operation. -To initiate operation, the process must be executing. -If the process is in ready state, it cannot be executing; hence must be in running state.

-Process scheduling allows more than one program/task to appear to be executed at the same time / enables multitasking / multiprogramming. -To allow high priority jobs to be completed first. -To keep the CPU busy all the time … to ensure that all processes execute efficiently … and to have reduced wait times for all processes / to ensure all processes have fair access to the CPU / prevent starvation of some processes.

Controls the selection of a program stored on disk to be removed into main memory. It decides which processes are loaded from the backing store into the memory/ready queue.