202308301340
Status: #idea
Tags: OS

Multi-programming system

• A process does IO while another does CPU
• Keeps multiple runnable jobs
• Overlaps IO of one with compute of another
• Benefits from I/O devices that can operate asynchronously
• Optimises system throughput at the cost of response time

flowchart LR

subgraph Queue

direction LR

J1\n0 --- J2\n1 --- J3\n2 --- J1\n12 --- J2\n18 --- J3\n15

end

subgraph CPU

direction LR

J1\n0-8 --- J2\n8-13 --- J3\n13-15 --- J1*\n15-18 --- J3*\n18-24 --- J2*\n24-33

end

Decision Points

1. Job completion
2. Process leaves for I/O
3. Job arrival (if the CPU is idle)

Problems

• If there is a CPU-bound job, IO bound jobs will starve

References