CPU Scheduling (FCFS)
Medium+14 XPWatch a Gantt chart fill in as the simplest scheduler runs jobs first-come, first-served — and see its flaw.
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There's one CPU but many processes that want it. The scheduler decides whose turn it is. Press Run to watch the simplest rule — First-Come-First-Served — build its timeline, and spot why it isn't always fair.
▸How do I read this chart?
Each ROW is a process; each COLUMN is one tick of time. A colored box in row P2, column 5 means 'P2 was using the CPU during time-slice 5.' Reading left to right shows you exactly who ran when — that's a Gantt chart.
▸What does First-Come-First-Served mean?
Exactly what it says: whoever asked first goes first, and runs all the way to the end before the next one gets a turn — like a single queue at a shop where nobody is allowed to cut in, and the cashier finishes one customer completely before starting the next.
▸What's the 'convoy effect' / why is FCFS not great?
If a big slow job is at the front, everyone behind it waits a long time — even if they only needed a second. Like getting stuck behind one person with a giant cart while you're holding a single item. FCFS is simple but can make short jobs wait far too long.
▸What's the fix?
Other schedulers! Round-Robin gives each process a small time-slice and rotates, so no one job hogs the CPU. Shortest-Job-First runs the quick ones first. Round-Robin is the very next topic — this FCFS chart is the baseline to compare against.