System Software

• An operating system provides a user interface, hides the hardware from applications and manages the computer’s resources.
• Key OS tasks: memory, file, security, hardware (input/output/peripherals) and process management.
• Utility software: disk formatter, virus checker, defragmenter, disk contents analysis/repair, file compression, back-up.
• Program libraries hold tested, reusable code; DLL files are linked when a program runs and shared between programs.
• An assembler translates assembly language; a compiler translates a whole high-level program into object code; an interpreter translates and runs one statement at a time.
• Some languages (such as Java) are partly compiled to intermediate bytecode and then interpreted by a virtual machine.
• An IDE supports coding, initial error detection, presentation and debugging.

The resource manager

Without an operating system every program would have to control the hardware directly. The OS provides an interface between the user and the computer (GUI or command line), and between application software and the hardware, so programs can use the disk, screen or printer through standard routines. It also manages the computer’s resources so several programs can run safely at once.

Housekeeping and reusable code

• Disk formatter: prepares a disk for use by setting up its file system (tracks, sectors, a directory structure); formatting also removes existing data and can check for bad sectors.
• Virus checker: scans files and memory for malware, comparing code with a database of known virus signatures and watching for suspicious behaviour (heuristics); quarantines or deletes infected files. Needs regular updates.
• Defragmentation software
• Disk contents analysis / disk repair
• File compression: reduces file size to save storage and transmission time, and can bundle files into one archive.
• Back-up software

program library