Without an operating system, every program would have to drive the hardware itself and fight other programs for memory and the processor. Learn why a computer system needs an OS and the five key management tasks it carries out.
An operating system (OS) is system software that manages the hardware and resources of a computer and provides a platform and an interface so that users and application programs can use the computer without controlling the hardware directly. Its key management tasks are memory management, file management, security management, hardware (input/output/peripheral) management and process management.
Fig. 1: the operating system's five management tasks, between the user and the hardware
Section 01
Why have an OS?
A bare computer is just hardware that obeys machine code. The OS turns it into something people and programs can actually use.
Hides the complexity of the hardware: application programmers call OS services (open a file, print, allocate memory) instead of writing code to control each device.
Provides a user interface: a GUI or command line interface lets the user start programs, manage files and change settings.
Shares resources fairly: many programs and users compete for the CPU, memory and devices; the OS allocates them and stops one program interfering with another.
Provides a platform for applications: the same application runs on any hardware that the OS supports.
Keeps the system secure and stable: controls who can log in and what each user and process may access.
Examiner trap
"The OS lets the computer run" earns nothing. Say what it provides: an interface for the user, a platform of services for applications, and management of the hardware and resources.
Section 02
Five management tasks.
The syllabus names five areas. For each one, learn two or three specific things the OS does: that is where the marks are.
Task
What the OS does
Memory management
allocates RAM to each process when it is loaded and frees it when the process ends; keeps track of which parts of memory are in use; protects each process's memory so one program cannot overwrite another's; uses virtual memory when RAM is full
File management
provides a file system and a hierarchical directory (folder) structure; names, creates, opens, saves, copies, moves and deletes files; records where each file is stored on secondary storage; controls access rights to files
Security management
user accounts with usernames and passwords; access rights (permissions) for files and folders; firewall; automatic security updates and patches; prevents unauthorised access to data and programs
Hardware management (input/output/peripherals)
communicates with devices through device drivers; handles interrupts from devices; manages buffers and queues (e.g. a print queue) so slow devices do not hold up the CPU
Process management
loads programs and creates processes; schedules processor time between processes so several can run (multitasking); handles priorities and interrupts; lets processes communicate and prevents deadlock
Examiner trap
Do not mix up the tasks. Allocating processor time is process management; allocating RAM is memory management.
Stage 1 · Learn
Check what the sim just showed you
Four quick checks. Each correct answer earns XP and records this skill on your profile.
Quick check+10 XP
Why does a computer system need an operating system?
Quick check+10 XP
Which management task shares processor time between programs?
Quick check+10 XP
Which is part of memory management?
Quick check+10 XP
How does the OS communicate with a peripheral device?
Section 03
Which task is it?
Exam questions often describe an event and ask which management task deals with it. Match the resource involved.
Worked example Match the task
Identify the OS management task in each case. (a) A user is told they cannot open a colleague's spreadsheet. (b) Five documents wait in turn to be printed. (c) A browser and a music player both appear to run at the same time. (d) A game is loaded and given 2 GiB of RAM.
(a) The OS checks the access rights for the file against the user's account: security management (access rights to files also feature in file management).
(b) The OS holds the jobs in a print queue and sends them to the printer through its driver: hardware (peripheral) management.
(c) The OS shares processor time between the two processes: process management.
(d) The OS allocates RAM to the new process and keeps it separate from other processes: memory management.