1.5

• Collection of software systems that manage the computer • Usually supplied with the computer

• Provides a platform to run programs • Provides an interface for user to interact with it • Maintain computer system

• Operating system • Utility software

• Provides a platform on which users can run and interact with programs • e.g. MacOS, iOS, Windows

• User interface • Memory management • Peripheral management • File management • User management

• Allows the user and the computer system to interact • Manages the use of input devices and software

• Graphical (GUI) • Command line • Menu driven • Natural language

• Windows, icons, menus, pointers (WIMP) • Visual • Interactive • Intuitive • Optimised for mouse and touch gesture input

• Text based • Less resource heavy • More commands • Efficient • For advanced users, used by network administrators • Useful for automating processes with scripts

• Successive menus presented to the user • Single options chosen at each stage • Often with buttons on a keypad

• Responds to questions in spoken language • Not always reliable because still developing

• Running multiple applications at the same time by giving each application a small time-slice of processor time • Allows more than one program held in memory at once

• When programs are loaded, OS keeps a record of where each program and its data are located • Virtual memory is used if RAM is full • Transfers instructions and data into memory when needed and to the hard disk when not

• Translates OS instructions into commands that the hardware will understand • Each peripheral needs own device driver

• The OS deals with input/output to and from any connected peripheral devices

• Allowing different users to log into the same computer • OS retains settings (e.g. backgrounds/icons, access rights) • Client server network may impose a fixed/roaming profile for a user

• Extension to filename tells the OS which application to load the file into • Presents a logical structure of files by using folders • Allows user to read, write, rename, duplicate, delete files • Facilitates access permissions for files (view/edit)

• To perform housekeeping/maintenance tasks • e.g. file backup, virus checking, compression program

• Turns plaintext into unreadable ciphertext using a key • Text can only be decrypted with a master key • Protects data from being read by hackers

• Rearranges parts of files and frees up contiguous space • Reduces the movement of a R/W head across the surface of the disk, speeds up file access

• Different sized files saved on disks are deleted over time, creating gaps • New files fill up the gaps but some may need more space than the gaps provides, resulting in fragments of files

• Reduce the size of a file • Takes up less space • Quicker to download over the Internet • Compressed files must be extracted before read • Lossy/lossless