IGCSE Computer Science 0478: Operating System Functions in a Shared Library Computer

A school library's shared computer runs a general-purpose operating system that many different students use throughout the day, often for more than one task at a time.

Situation 1: Each student logs in with their own username and password. Once logged in, a student can open, edit and delete the files in their own personal folder, but cannot open another student's folder or change the settings that control the whole computer.

Situation 2: While one student researches a project in a web browser, another window has a document open in a word processor. The operating system repeatedly decides, many times every second, which of the two programs gets to use the processor next, so that both appear to run at the same time.

Situation 3: While the browser and the word processor are both open, the operating system keeps track of which area of RAM each program is using, and stops one program from reading or overwriting the memory that belongs to the other program.

(a) Identify the operating system function shown in Situation 1, and describe how it protects each student's work. [3]

(b) Identify the operating system function shown in Situation 2, and describe how it allows both programs to appear to run at once. [2]

Part (a): Situation 1. User management

Each student’s personal login and password, and the fact that they can only reach their own files and not the whole computer’s settings, describes user management. The operating system maintains a separate account for every student, checks the username and password at login, and restricts what each account is allowed to see and change. This keeps one student’s files private from other students and stops ordinary students from altering system-wide settings.

Part (b): Situation 2, multitasking

Having a browser and a word processor both appear to run at once on one computer describes multitasking, a form of processor (resource) management. The operating system does not truly run both programs at the exact same instant; instead, it rapidly shares out the processor’s time between them, giving each program a short turn many times per second. Because the switching happens so fast, the user sees both programs responding as though they are running simultaneously.

Part (c): Situation 3, memory management

Tracking which part of RAM belongs to which open program, and stopping one program from reading or overwriting another program’s memory, describes memory management. This is needed because several programs are held in RAM at once while the computer multitasks; without the operating system keeping their memory areas separate, one program could corrupt another program’s data or code, causing incorrect results or a crash.

Final answers

(a) User management, separate, password-protected accounts, each restricted to its own files and a limited set of settings, keep every student’s work private and the whole computer’s settings safe.
(b) Multitasking (processor management). The processor’s time is rapidly shared between the two programs so that both appear to run at once, even though only one is actually being processed at any instant.
(c) Memory management. The operating system tracks which RAM belongs to which program and prevents one program from overwriting another’s memory, which is needed to stop programs corrupting each other and crashing.