Topic 5 · Resource Management (HL)

Manages hardware/software resources. The referee between apps and hardware.

Program = file on disk. Process = running instance with its own memory, state, and PID.

NEW → READY → RUNNING → (BLOCKED ↔ READY) → TERMINATED.

Process waiting for I/O. OS runs something else meanwhile — that's why I/O doesn't waste CPU.

Save current state to PCB + load next process's state. Costs microseconds + pollutes caches.

First-Come-First-Served. Simple. Convoy effect: one long job blocks shorter ones behind it.

Shortest Job First. Optimal AVERAGE wait. Risk: long jobs STARVE; OS may not know job lengths.

Fixed time slice (e.g. 10 ms) per process; rotate. Best for INTERACTIVE systems (laptops, phones).

Highest priority runs. Best for REAL-TIME deadlines. Risk: low-priority STARVATION (fix: aging).

Real OSes combine RR + priority + aging. Linux, Windows, macOS all do this.

Shorter slice = more responsive but more context-switch overhead. Bigger = vice versa.