Summer 2023Q4(A)
Explain how free space can be managed by OS.
Chapter 4
Memory Allocation and Free-Space Management
Compare fixed/dynamic partitions and first-fit, next-fit, best-fit, worst-fit strategies.
Estimated time: 26 min
Allocation algorithms decide where a new process gets placed in available memory holes.
Allocation numericals are common and connect directly to fragmentation and utilization.
Partitioning Models
From notesClear explanation
Fixed partitions are simple but rigid; dynamic partitions improve usage but create fragmented holes.
What it really means
Fixed seats vs adjustable tables in a restaurant.
Key takeaway
Flexibility improves utilization but increases management complexity.
Allocation Strategy Trade-off
From notesClear explanation
First-fit is fastest, best-fit can reduce waste, and worst-fit tries preserving medium holes but often performs poorly.
What it really means
Placement policy changes future placement options.
Key takeaway
Always discuss both speed and fragmentation impact.
First-Fit / Best-Fit / Worst-Fit Working
Added clarityClear explanation
First-fit picks first sufficient hole, best-fit picks smallest sufficient hole, worst-fit picks largest hole.
What it really means
You are choosing where to park a car in available slots: nearest slot, tightest slot, or widest slot.
Example
Request 200KB in free blocks [300, 220, 700]: first-fit->300, best-fit->220, worst-fit->700.
Key takeaway
Same request can leave very different future hole patterns.
- - Using best-fit without full search
- - Ignoring that worst-fit may fail despite large total free memory
- - Confusing internal and external fragmentation
- - First-fit is fast, best-fit minimizes leftover but scans more
- - Dynamic partitions adapt size but create external fragmentation
- - Free space can be tracked via bitmap or linked list
Internal fragmentation = allocated block size - requested size
External fragmentation = total free memory exists but not in one contiguous block
Exam lens for this topic
What evaluators usually expect in structured exam answers.
Must-use keywords
- - memory allocation
- - first fit
- - next fit
- - best fit
- - worst fit
Answer flow
- - Write exact definition in first line
- - Explain mechanism in ordered bullets
- - Add one short example or scenario
- - Close with key takeaway and one exam keyword
Practice Questions
Place process sizes 115, 500, 358, 200, 375 KB using first-fit, best-fit, worst-fit.
Source: Summer 2023 Q4(C) OR
Answer focus: Correct block selection sequence and final free blocks.
Solve first-fit, best-fit, and worst-fit allocation for given six partitions.
Source: Summer 2024 Q4(B)
Answer focus: Stepwise allocation table and efficiency comparison.
Practice from papers (end-of-topic set)
These paper questions map directly to this topic. Solve now, then compare your structure with linked topics.
Summer 2023Q4(C) OR
Demonstrate first-fit, best-fit, worst-fit placement for given process sizes and partitions, and identify efficient algorithm.
Winter 2023Q4(B)
Explain virtual memory with the help of diagram.
Winter 2023Q4(B) OR
Describe fixed and variable memory allocation in short.
Summer 2024Q4(B)
Given six partitions and process sizes, solve first-fit, best-fit and worst-fit placement.
Summer 2024Q4(B) OR
Using given allocation/max table and available vector, apply Banker's algorithm: find Need, safety, and request grant check.
Winter 2024Q4(B)
Given six partitions and process sizes, solve first-fit, best-fit, and worst-fit placement.
Winter 2024Q4(B) OR
Using given allocation/max table and available vector, apply Banker's algorithm: Need, safe state, and request grant check.
Summer 2025Q4(A)
What is memory? Explain different types of memory.
Summer 2025Q4(B)
Explain first-fit memory allocation algorithm with example.
Summer 2025Q4(B) OR
Explain best-fit memory allocation algorithm with example.
Question Bank Linked Here
Open all questionsSummer 2023Q4(A)
Explain how free space can be managed by OS.
Summer 2023Q4(C) OR
Demonstrate first-fit, best-fit, worst-fit placement for given process sizes and partitions, and identify efficient algorithm.
Winter 2023Q4(B)
Explain virtual memory with the help of diagram.
Winter 2023Q4(B) OR
Describe fixed and variable memory allocation in short.
Summer 2024Q4(B)
Given six partitions and process sizes, solve first-fit, best-fit and worst-fit placement.
Summer 2024Q4(B) OR
Using given allocation/max table and available vector, apply Banker's algorithm: find Need, safety, and request grant check.
Winter 2024Q4(B)
Given six partitions and process sizes, solve first-fit, best-fit, and worst-fit placement.
Winter 2024Q4(B) OR
Using given allocation/max table and available vector, apply Banker's algorithm: Need, safe state, and request grant check.
Summer 2025Q4(A)
What is memory? Explain different types of memory.
Summer 2025Q4(B)
Explain first-fit memory allocation algorithm with example.
Summer 2025Q4(B) OR
Explain best-fit memory allocation algorithm with example.
How to answer linked exam questions
Full question bankSummer 2023 Q4(A)
Explain how free space can be managed by OS.
Answer pattern: concept -> intuition -> steps -> concluding point with one application.
Summer 2023 Q4(C) OR
Demonstrate first-fit, best-fit, worst-fit placement for given process sizes and partitions, and identify efficient algorithm.
Answer pattern: concept -> intuition -> steps -> concluding point with one application.
Winter 2023 Q4(B)
Explain virtual memory with the help of diagram.
Answer pattern: start with definition, draw neat labeled diagram, then explain flow/parts.
Winter 2023 Q4(B) OR
Describe fixed and variable memory allocation in short.
Answer pattern: concept -> intuition -> steps -> concluding point with one application.
Summer 2024 Q4(B)
Given six partitions and process sizes, solve first-fit, best-fit and worst-fit placement.
Answer pattern: define briefly, then solve stepwise and show final values/table.
Summer 2024 Q4(B) OR
Using given allocation/max table and available vector, apply Banker's algorithm: find Need, safety, and request grant check.
Answer pattern: concept -> intuition -> steps -> concluding point with one application.