Memory Allocation Strategies: First Fit, Best Fit, Worst Fit

Deciding Which Free Gap a New Process Should Use

Under dynamic partitioning (covered earlier in this section), several free gaps of different sizes may exist at once. When a new process needs memory, the OS must choose which specific free gap to place it in - three classic strategies answer this differently.

A Shared Example for All Three

Free gaps available:  Gap A: 20k    Gap B: 8k    Gap C: 15k
New process needs:    10k

First Fit: The First Gap That's Big Enough

First Fit scans through gaps in order and picks the very first one large enough to fit the request - in this example, Gap A (20k), simply because it's encountered first and is big enough. It's fast, since scanning can stop the moment a suitable gap is found.

Best Fit: The Smallest Gap That's Still Big Enough

Best Fit scans every gap and picks the smallest one that's still large enough - in this example, Gap C (15k), since it's the tightest possible fit. This minimizes leftover wasted space in that specific gap, but requires examining every gap first.

Worst Fit: The Largest Available Gap

Worst Fit deliberately picks the largest available gap - in this example, Gap A (20k) again, but for a completely different reason than First Fit: the idea is that using the biggest gap leaves the largest possible leftover space, which might be more useful for a future request.

Comparing All Three Strategies

Why No Single Strategy Is Universally "Best"

Each strategy performs differently depending on the actual pattern of process sizes and free gaps in a real system - which is exactly why this remains a genuinely studied trade-off, rather than one strategy having simply replaced the other two entirely.