1.2.1a+b+c+d – Systems Software - Done

Operating systems enable the user to communicate with the computer and ensure the computer runs efficiently.

• Resource management / File management • Memory management • Scheduling • Interrupt handling • Provides security / user management • Providing a platform to install and run software • Providing a user interface • Providing utilities for system maintenance • Peripheral management

Memory management means to ensure that RAM is used efficiently and not wasted. Features of memory management include removing unneeded data, allocating memory to applications, managing virtual storage and paging and segmentation.

The operating system must track all devices connected to the system and provide device drivers to enable the computer to communicate with any peripherals.

Data is stored in files in secondary storage. The operating systems allows users to rename, delete, copy, search for, and move files and folders.

The OS controls who can access the system and certain resources within it through managing access rights.

The OS provides an interface which allows the user to interact with the software

The OS provides utilities in order to maintain the computer and to manage the security

The OS allows additional software to be installed on the computer to allow the user to complete additional tasks.

Paging is a memory management method that splits memory into fixed size memory blocks called pages. It also utilises physical addressing, meaning memory is divided physically. It enables the use of virtual memory.

• Data can be held in non-contiguous memory locations • Makes it easier to make best use of remaining storage as you avoid having to move content around to fit in new programs • Allows pages to be transferred to and from secondary storage • As it’s random access there is no performance drop vs sequential storage

• Unused space may be wasted inside a page, this results in internal fragmentation

Segmentation is a form of memory management in which programs are divided into variable length memory blocks. It uses logical addressing, meaning memory is divided logically.

• It’s space-efficient as it only allocates space depending on the amount an application needs • Easier to organise a program into complete sections

• It can leave small unused gaps in memory that can’t easily be filled by other data, this causes external fragmentation • Segmentation errors can cause memory leakage which would cause the system to crash

Virtual memory is used when RAM is full to enable applications to run. Data is transferred out of RAM into virtual memory to free up space and transferred back again when needed.

• Allows the user to run programs when physical memory is full • It frees up space in RAM for programs currently in use, rather than having unused programs take up space in RAM

• As the secondary storage is further from the CPU than the main memory programs stored in virtual memory take longer to load • Disk thrashing can occur if more time is spent moving pages between main memory and the hard disk than time spent processing instructions. This will cause the computer to run very slowly and even ‘freeze’. The issue becomes progressively worse as virtual memory is filled up.

• Security, as it does not let programs access memory reserved for other programs • Multitasking, as it allows multiple programs to run at once

Interrupts are signals generated by software or hardware to indicate to the processor that a process needs attention more urgently than the current task does.

Interrupts can come from hardware or software and have varying priorities. They can result in changes in files (e.g. their removal or transfer), windows, the pointer, icons and other features. These changes are carried out by computers components and systems such as the GUI, OS or CPU.

• An interrupt is checked for at the start/end of each FDE cycle. • If the interrupt is of a higher priority than the current process, the contents of the registers are copied to a stack. (otherwise the current process continues) • The Interrupt Service Routine then runs. • After the interrupt is complete, the previous register values are restored back from the stack.

Scheduling is used by the CPU to decide the order in which processes are executed. Scheduling aims to manage CPU time efficiently and ensure all programs receive a fair share of resources.

• Round Robin • First Come First Served • Multi-level Feedback Queues • Shortest Job First • Shortest Remaining Time