System resources

Key resources a system must manage:

• Primary memory (RAM) and secondary storage (disk capacity).
• Processor speed and number of cores.
• Bandwidth and network connectivity.
• Cache, screen resolution, sound and graphics processors.

Every resource is finite, so demand can exceed supply and must be scheduled and prioritised.

Role of the operating system

The operating system (OS) manages resources so programs and users can share the machine:

• Memory management — allocate and protect memory between programs.
• Processor management — schedule which process runs next.
• Peripheral / device management — control input and output devices.
• Security and file management.

Who or what handles it?

Tap an item, then the category it belongs to.

Paging and virtual memory

To run programs larger than physical RAM, the OS uses virtual memory: part of the disk is used as if it were extra RAM. Memory is divided into fixed-size pages that are swapped between RAM and disk as needed (paging).

Too much paging causes thrashing, where the system spends more time swapping than computing, and slows dramatically.

Virtual memory

Scheduling and multitasking

Multitasking lets several processes appear to run at once. The scheduler gives each a slice of CPU time and switches quickly between them. Different scheduling policies (round-robin, priority) balance fairness and responsiveness.

Scheduling

Interrupts and polling

Devices signal the CPU in two ways:

• Interrupt — the device sends a signal that makes the CPU pause, save its state and run an interrupt handler. Efficient: the CPU only reacts when needed.
• Polling — the CPU repeatedly checks each device. Simple, but wastes cycles when nothing has happened.

Interrupt vs polling

Dedicated systems

A dedicated (embedded) system is built for one task — a smart thermostat, an ATM, a washing-machine controller. It has limited, fixed resources and a specialised OS, so resource management is simpler but tightly constrained.

Screen memory

Match the OS job

Tap a description on the left, then the OS function.

The memory hierarchy

Memory forms a hierarchy, fastest and smallest first: registers, cache, RAM, then secondary storage. Cache holds recently and frequently used data close to the CPU. A high cache hit rate means most requests are served from fast cache, greatly improving performance.

Cache purpose

Screen memory (2)

The big ideas to know

You have covered the key ideas in Topic 6 — resource management. Press Finish to see your score.