Various Allocation Methods in Contiguous Memory Management

Introduction

• 4 algorithms for allocating memory to processes:
  • First Fit
  • Next Fit
  • Best Fit
  • Worst Fit

Scenario Setup

• Memory contains processes and available holes (leftover space)
• Processes: P10, P11, P12, P13, P14, P15
• Objective: Allocate processes in available holes using different algorithms

First Fit Algorithm

• Concept: Allocate the first hole that is big enough
• Example:
  • Process P1 of size 15K
  • Find the first hole of 25K to allocate P1
  • Searching stops as soon as a suitable hole is found
• Advantages:
  • Easiest and fastest method
  • Minimal searching time
• Disadvantages:
  • May create large leftover holes, leading to inefficient usage of memory

Next Fit Algorithm

• Concept: Same as First Fit, but starts searching from the last allocated hole
• Example:
  • P1 allocated to a 25K hole
  • When P2 (18K) arrives, starts searching from 25K hole onwards
  • Finds a 40K hole and allocates P2
• Advantages: Faster than First Fit when dealing with multiple allocations as it avoids repeated searches from the beginning

Best Fit Algorithm

• Concept: Search entire list and choose hole that results in minimum internal fragmentation
• Example:
  • Process P1 of size 15K
  • Searches all holes, tries to minimize leftover space
  • Allocates to a 20K hole, leaving 5K leftover
• Advantages: Minimizes internal fragmentation
• Disadvantages:
  • Very slow due to exhaustive search
  • May create tiny holes that are unusable for larger processes

Worst Fit Algorithm

• Concept: Select the largest hole available
• Example:
  • Process P1 of size 15K
  • Allocates to 100K hole, leaving 85K leftover
• Advantages:
  • Keeps large leftover spaces which can accommodate future processes
• Disadvantages:
  • Slow due to need to search entire list

Comparison

• First Fit:
  • Easiest, fastest
  • May create many small leftover holes
• Next Fit:
  • Modified First Fit
  • Faster as it avoids repeated searches from start
• Best Fit:
  • Minimizes internal fragmentation
  • Very slow, may create tiny unusable holes
• Worst Fit:
  • Opposite of Best Fit
  • Keeps large leftover spaces, but also slow

Conclusion

• First Fit is generally the most convenient method due to speed
• Depending on scenario, any algorithm might be best suited
• Important to understand the working principles of these algorithms for practical application