Memory Management

Memory Allocation

First Fit and Best Fit placement strategies for variable memory block partition management.

What is Memory Allocation?

Memory Allocation strategies manage variable partition layouts of RAM. First Fit searches sequentially and assigns a process to the first free block large enough. Best Fit searches all partitions and assigns the process to the block that results in the smallest leftover fragment space, preserving large blocks for future processes.

Key Characteristics:

  • First Fit: Fast execution speed; skips searching the entire block list.
  • Best Fit: Reduces size wastage, but increases memory fragmentation overhead.
  • Simulates dynamic partition allocation maps.
  • Essential for managing multi-programmed memory spacing.

Complexity Analysis

Avg Time Complexity: O(P * B) where P is processes count and B is memory blocks count
Space Complexity: O(B) memory structures
Best Case: O(P) (First Fit finding compatible block at index 0 immediately)
Worst Case: O(P * B) (Best Fit scanning all partitions to minimize waste)

How it Works Step-by-Step

  1. Read Request: Note the memory requirement of the current process.
  2. First Fit: Search partitions from left to right. Allocate the first block index j where BlockSize[j] >= ProcessSize[i].
  3. Best Fit: Scan all partitions. Select block index j that minimizes BlockSize[j] - ProcessSize[i] while meeting size requirement.
  4. Deduct Space: Subtract process requirement from partition size, and flag block as occupied.
  5. Proceed: Repeat for subsequent processes.

Code Implementation

Worked Trace Example

Blocks: [100, 500, 200]. Process sizes: [150, 450]:
- First Fit: Process 150 goes to block 500 (remains 350). Process 450 cannot fit anywhere (unallocated).
- Best Fit: Process 150 goes to block 200 (remains 50). Process 450 goes to block 500 (remains 50). All allocated.
Result: Best Fit solved allocation whereas First Fit failed.

Ready to Understand Memory Allocation Visually?

Don't just read about it. Launch our interactive, premium OS visualizer to see the processes, memory blocks, Page replacement queues, or disk head movements update in real-time.

Launch Memory Allocation Visualizer →