Operating Systems

Process ID, state, program counter, CPU registers, scheduling info — everything needed for a context switch

Completion Time − Arrival Time

Turnaround Time − Burst Time

SJF (Shortest Job First) — short jobs keep jumping the queue ahead of it

Mutual Exclusion, Hold and Wait, No Preemption, Circular Wait — ALL 4 must hold simultaneously

Deadlock avoidance — checks whether granting a resource request keeps the system in a 'safe state'

A mutex has ownership (only the locking thread can unlock it); a semaphore is a general counter any thread can signal

With FIFO page replacement specifically, adding more frames can sometimes cause MORE page faults, not fewer

Internal fragmentation (the last page may be only partially filled)

External fragmentation

Too many processes competing for too little physical memory — the degree of multiprogramming is too high

Reduce the degree of multiprogramming

The Elevator Algorithm — the head moves in one direction, reverses at the end

Recent page-table lookups, avoiding a full memory access for every address translation