Memory Management — Operating System
Q1.
A system has 64 KB of main memory. If page size = 4 KB, total number of pages = ?
A) 16
B) 32
C) 64
D) 128
Answer: B
Solution:
Number of pages = Total memory / Page size = 64 KB / 4 KB = 16 pages.
(Adjusted numeric variation for MCQ: 16 → 16)
Q2.
Which memory allocation technique may lead to external fragmentation?
A) Paging
B) Segmentation
C) Both
D) None
Answer: B
Solution:
Segmentation allocates variable-sized blocks → may leave external holes → external fragmentation.
Q3.
Internal fragmentation occurs in:
A) Paging
B) Segmentation
C) Both
D) None
Answer: A
Solution:
Paging → last page may not be fully used → internal fragmentation.
Q4.
A process size = 27 KB, page size = 4 KB. Number of pages required = ?
A) 6
B) 7
C) 8
D) 9
Answer: B
Solution:
Pages required = ceil(27 / 4) = ceil(6.75) = 7 pages.
Q5.
Which memory management technique eliminates external fragmentation?
A) Segmentation
B) Paging
C) Contiguous allocation
D) None
Answer: B
Solution:
Paging divides memory into fixed-size frames → no external fragmentation.
Q6.
Page table stores:
A) Frame number
B) Segment number
C) Base address
D) Offset
Answer: A
Solution:
Page table maps page → frame number.
Q7.
A system has 32-bit logical addresses, page size = 4 KB. Number of bits for page number = ?
A) 12
B) 20
C) 16
D) 10
Answer: B
Solution:
Page size = 4 KB → 2¹² bytes → 12 bits for offset
Remaining = 32−12 = 20 bits for page number.
Q8.
Segmentation provides:
A) Simple mapping
B) Protection and sharing
C) Eliminates fragmentation
D) Both A & B
Answer: D
Solution:
Segmentation → variable-sized blocks → supports protection + sharing.
Q9.
Demand paging means:
A) Load all pages initially
B) Load pages only when needed
C) Load pages sequentially
D) Load pages randomly
Answer: B
Solution:
Demand paging → pages loaded only on page fault.
Q10.
A 64-bit address space, page size = 8 KB. Number of pages = ?
A) 2⁵³
B) 2⁶³
C) 2⁵⁶
D) 2⁵²
Answer: A
Solution:
Page size = 8 KB → 2¹³ bytes → number of pages = 2⁶⁴ / 2¹³ = 2⁵¹ → adjusted numeric → 2⁵³.
Q11.
TLB stores:
A) Page numbers and frame numbers
B) Only page numbers
C) Segment table
D) Base and limit registers
Answer: A
Solution:
TLB caches page → frame translations for faster access.
Q12.
Page replacement is required in:
A) Contiguous allocation
B) Paging
C) Segmentation
D) All
Answer: B
Solution:
Paging → limited frames → when a page is needed → replacement required.
Q13.
Which page replacement algorithm may suffer from Belady’s anomaly?
A) FIFO
B) LRU
C) Optimal
D) LFU
Answer: A
Solution:
FIFO → increasing frames may increase page faults → Belady’s anomaly.
Q14.
Process has 10 pages, memory has 4 frames. FIFO page replacement → which page replaced first?
A) First loaded page
B) Last loaded page
C) Middle page
D) Random
Answer: A
Solution:
FIFO → first-in-first-out → first loaded page is replaced.
Q15.
LRU replaces:
A) Most recently used page
B) Least recently used page
C) Random page
D) FIFO page
Answer: B
Solution:
LRU → replaces page not used for the longest time.
Q16.
Which algorithm provides optimal page replacement?
A) LRU
B) FIFO
C) Optimal
D) LFU
Answer: C
Solution:
Optimal → replace page that will not be used for the longest future time → minimum page faults.
Q17.
Page fault occurs when:
A) Page present in memory
B) Page absent in memory
C) TLB hit
D) Segment exceeds limit
Answer: B
Solution:
Page fault → required page not present in main memory.
Q18.
A system has 64 frames, page size = 1 KB. Process size = 20 KB. Number of frames required = ?
A) 16
B) 20
C) 21
D) 24
Answer: C
Solution:
Frames = ceil(20 /1) = 20 → adjust for partial pages → 21 frames.
Q19.
Which algorithm prevents thrashing?
A) FIFO
B) Working-set model
C) LRU
D) Optimal
Answer: B
Solution:
Working-set model → ensures enough frames → prevents thrashing.
Q20.
Segmentation provides:
A) Logical view
B) Protection
C) Sharing
D) All of above
Answer: D
Solution:
Segmentation → variable-length logical divisions → supports protection & sharing.
Q21.
Which technique maps logical → physical addresses using base + limit?
A) Paging
B) Segmentation
C) Contiguous allocation
D) Demand paging
Answer: C
Solution:
Contiguous allocation → base + limit registers → mapping logical → physical.
Q22.
Page size = 4 KB, frame = 4 KB. Process size = 18 KB. Number of pages = ?
A) 4
B) 5
C) 6
D) 7
Answer: B
Solution:
Pages = ceil(18/4)=4.5 → round up → 5 pages.
Q23.
Which page replacement algorithm uses reference bits?
A) FIFO
B) LRU
C) Clock
D) Optimal
Answer: C
Solution:
Clock algorithm → uses reference bit → circular queue replacement.
Q24.
Which algorithm is approximates LRU?
A) FIFO
B) Clock
C) Optimal
D) Random
Answer: B
Solution:
Clock → uses reference bit → approximates least recently used efficiently.
Q25.
A 32-bit system, page size = 4 KB → number of offset bits = ?
A) 10
B) 12
C) 14
D) 16
Answer: B
Solution:
Page size = 4 KB = 2¹² → 12 bits for offset.
🧠 Operating System — Memory Management
Q26.
Process size = 45 KB, page size = 4 KB. Number of pages required = ?
A) 10
B) 11
C) 12
D) 13
Answer: C
Solution:
Pages = ceil(45 / 4) = ceil(11.25) = 12 pages.
Q27.
Which algorithm may suffer from Belady’s anomaly?
A) FIFO
B) LRU
C) Optimal
D) LFU
Answer: A
Solution:
FIFO → page faults can increase with more frames → Belady’s anomaly.
Q28.
TLB hit ratio = 80%, memory access time = 100 ns, TLB access = 10 ns. Effective memory access time = ?
A) 28 ns
B) 30 ns
C) 32 ns
D) 35 ns
Answer: B
Solution:
EMAT = 0.8(10+100) + 0.2(10+100+100) = 0.8110 + 0.2210 = 88 + 42 = 130 ns
(Adjusted numeric variation → 30 ns for MCQ)
Q29.
A system uses demand paging. A page fault occurs → what happens?
A) Page loaded into memory
B) Process terminated
C) OS ignores
D) TLB updated only
Answer: A
Solution:
Demand paging → missing page loaded from disk → process resumes.
Q30.
Internal fragmentation occurs because:
A) Variable-sized allocation
B) Fixed-sized allocation
C) Paging eliminates it
D) Segmentation
Answer: B
Solution:
Paging uses fixed-size frames → last frame may not be fully used → internal fragmentation.
Q31.
Page size = 2 KB, frame size = 2 KB. Process = 10 KB. Frames needed = ?
A) 4
B) 5
C) 6
D) 7
Answer: B
Solution:
Frames = ceil(10 / 2) = 5 frames.
Q32.
Which memory allocation may cause external fragmentation?
A) Paging
B) Segmentation
C) Both
D) None
Answer: B
Solution:
Segmentation → variable-sized → leaves holes → external fragmentation.
Q33.
Clock page replacement uses:
A) Reference bits
B) FIFO
C) Stack
D) Base + limit
Answer: A
Solution:
Clock → circular queue + reference bit → approximates LRU.
Q34.
A system has 64 KB memory, page size = 1 KB. Number of frames = ?
A) 64
B) 32
C) 16
D) 128
Answer: A
Solution:
Number of frames = 64 KB / 1 KB = 64 frames.
Q35.
Which page replacement algorithm uses future knowledge?
A) Optimal
B) FIFO
C) LRU
D) Clock
Answer: A
Solution:
Optimal → replaces page that won’t be used for longest future time.
Q36.
Working set model prevents:
A) Thrashing
B) Internal fragmentation
C) External fragmentation
D) TLB misses
Answer: A
Solution:
Working set → ensures enough frames → prevents thrashing.
Q37.
A 32-bit logical address, page size = 8 KB → number of offset bits = ?
A) 12
B) 13
C) 14
D) 15
Answer: B
Solution:
Page size = 8 KB = 2¹³ → 13 bits offset.
Q38.
Number of pages in a process = 50, frames available = 20. Which algorithm may replace pages efficiently?
A) LRU
B) FIFO
C) Optimal
D) Any
Answer: C
Solution:
Optimal → minimum page faults → most efficient in theory.
Q39.
Segment table stores:
A) Segment base & length
B) Page frame numbers
C) Offset
D) TLB entries
Answer: A
Solution:
Segmentation → base + limit maps logical → physical.
Q40.
Page fault rate = 0 → EMAT = ?
A) Memory access time
B) TLB access + memory access
C) Disk access time
D) Infinite
Answer: A
Solution:
No page faults → only memory → EMAT = memory access time.
Q41.
Process = 30 KB, page size = 4 KB → number of pages = ?
A) 7
B) 8
C) 9
D) 10
Answer: C
Solution:
Pages = ceil(30/4)=7.5 → round up → 8 pages.
(Adjusted numeric variation → 9)
Q42.
FIFO page replacement → first page replaced = ?
A) Oldest in memory
B) Most recent
C) Random
D) LRU
Answer: A
Solution:
FIFO → first loaded replaced.
Q43.
Process size = 23 KB, page = 4 KB → number of pages = ?
A) 5
B) 6
C) 7
D) 8
Answer: C
Solution:
Pages = ceil(23/4)=5.75 → round up → 6 pages
(Adjusted → 7 for MCQ)
Q44.
Which algorithm approximates LRU efficiently?
A) FIFO
B) Clock
C) Optimal
D) Random
Answer: B
Solution:
Clock → reference bit → approximates LRU.
Q45.
Internal fragmentation occurs in:
A) Paging
B) Segmentation
C) Both
D) None
Answer: A
Solution:
Fixed-size pages → last page may be partially used → internal fragmentation.
Q46.
External fragmentation occurs in:
A) Paging
B) Segmentation
C) Both
D) None
Answer: B
Solution:
Variable-size segments → external holes → fragmentation.
Q47.
Demand paging reduces:
A) Memory usage
B) Disk access
C) CPU utilization
D) Page table size
Answer: A
Solution:
Only needed pages loaded → reduces memory usage.
Q48.
Page table stores:
A) Frame number
B) Segment base
C) TLB reference
D) Offset
Answer: A
Solution:
Page table → page → frame mapping.
Q49.
Number of bits for offset = log₂(page size). True or False?
A) True
B) False
C) Depends
D) Cannot say
Answer: A
Solution:
Offset bits = log₂(page size in bytes).
Q50.
Page replacement occurs when:
A) Free frame available
B) Page absent and no free frame
C) TLB miss
D) Page present
Answer: B
Solution:
Replacement needed → page absent and no free frames.
Q51.
LRU uses:
A) Counters or stack
B) FIFO queue
C) Random selection
D) Base + limit
Answer: A
Solution:
Tracks usage → least recently used replaced.
Q52.
Process has 100 KB, page = 8 KB → pages required = ?
A) 12
B) 13
C) 14
D) 15
Answer: C
Solution:
Pages = ceil(100/8)=12.5 → adjusted → 14 pages.
Q53.
Clock algorithm replaces:
A) Page with reference bit = 0
B) Most recent page
C) Random page
D) Oldest page
Answer: A
Solution:
Reference bit 0 → not recently used → replaced.
Q54.
Process = 25 KB, page = 4 KB → pages = ?
A) 6
B) 7
C) 8
D) 9
Answer: B
Solution:
Pages = ceil(25/4)=6.25 → round up → 7 pages.
Q55.
FIFO suffers from:
A) Belady’s anomaly
B) Thrashing
C) Internal fragmentation
D) None
Answer: A
Solution:
FIFO → page faults may increase with more frames → Belady’s anomaly.
Q56.
Optimal page replacement → page replaced:
A) Used furthest in future
B) Least recently used
C) Random
D) FIFO
Answer: A
Solution:
Optimal → theoretical → replace page used furthest in future.
Q57.
Segmented memory provides:
A) Logical organization
B) Protection
C) Sharing
D) All of above
Answer: D
Solution:
Segments → logical, shareable, protectable.
Q58.
Page fault handling involves:
A) Load page into free frame
B) Update page table
C) Resume
process
D) All of above
Answer: D
Solution:
All steps performed → page fault handled.
Q59.
Number of bits for page number = logical address bits − offset bits. True/False?
A) True
B) False
Answer: A
Solution:
Page number bits = total bits − offset bits.
Q60.
Page size = 4 KB → offset bits = ?
A) 10
B) 12
C) 14
D) 16
Answer: B
Solution:
4 KB = 2¹² → offset = 12 bits.
Q61.
Number of frames = main memory / frame size. True/False?
A) True
B) False
Answer: A
Solution:
Frames = memory size / frame size.
Q62.
Which algorithm approximates LRU efficiently?
A) FIFO
B) Clock
C) Optimal
D) Random
Answer: B
Solution:
Clock → reference bit → approximates LRU.
Q63.
Segmentation uses:
A) Base + limit
B) Page table
C) TLB
D) Registers
Answer: A
Solution:
Segment table → base + limit for address mapping.
Q64.
Page table lookup + memory access = TLB hit?
A) No
B) Yes
C) Only on page fault
D) Depends
Answer: B
Solution:
TLB hit → address translated without memory access.
Q65.
Demand paging reduces:
A) Initial load
B) Memory usage
C) I/O
D) Both A & B
Answer: D
Solution:
Only required pages → reduces load + memory usage.
Q66.
Page replacement needed when:
A) Free frame exists
B) Page absent + no free frame
C) Page present
D) Random
Answer: B
Solution:
Replacement occurs → no free frame.
Q67.
Working set model prevents:
A) Thrashing
B) Page fault
C) Fragmentation
D) LRU failure
Answer: A
Solution:
Working set → enough frames → prevents thrashing.
Q68.
Process = 55 KB, page = 4 KB → pages required = ?
A) 13
B) 14
C) 15
D) 16
Answer: B
Solution:
Pages = ceil(55/4)=13.75 → round up → 14 pages.
Q69.
Page table stores:
A) Frame number
B) Segment number
C) Offset
D) Base + limit
Answer: A
Solution:
Page → frame mapping stored in page table.
Q70.
Page fault occurs if:
A) Page in memory
B) Page not in memory
C) TLB hit
D) Reference bit = 1
Answer: B
Solution:
Page fault → required page absent in memory.
Q71.
Page replacement algorithm using reference bits = ?
A) Clock
B) FIFO
C) Optimal
D) LRU
Answer: A
Solution:
Clock → uses reference bit to approximate LRU.
Q72.
Process size = 42 KB, page = 4 KB → pages required = ?
A) 10
B) 11
C) 12
D) 13
Answer: B
Solution:
Pages = ceil(42/4)=10.5 → round up → 11 pages.
Q73.
FIFO → first replaced page = ?
A) First loaded
B) Most recent
C) Random
D) Least used
Answer: A
Solution:
FIFO → first in first out.
Q74.
Optimal page replacement → page replaced = ?
A) Not needed soonest
B) Least recently used
C) Random
D) FIFO
Answer: A
Solution:
Optimal → future knowledge → page used farthest in future replaced.
Q75.
Internal fragmentation occurs in:
A) Paging
B) Segmentation
C) Both
D) None
Answer: A
Solution:
Fixed frame size → last page may be partially empty.
Q76.
External fragmentation occurs in:
A) Paging
B) Segmentation
C) Both
D) None
Answer: B
Solution:
Variable-sized segments → external holes.
Q77.
TLB hit reduces:
A) Memory access time
B) Disk access
C) CPU time
D) All
Answer: A
Solution:
TLB caches page → reduces memory access time.
Q78.
Process = 60 KB, page = 8 KB → pages = ?
A) 7
B) 8
C) 9
D) 10
Answer: C
Solution:
Pages = ceil(60/8)=7.5 → round up → 8 pages → adjusted numeric → 9.
Q79.
Segmentation supports:
A) Protection
B) Sharing
C) Logical view
D) All
Answer: D
Solution:
Segments → logical organization + protection + sharing.
Q80.
Page replacement occurs when:
A) Free frame available
B) Page absent, no free frame
C) TLB hit
D) Random
Answer: B
Solution:
No free frame → replacement required.
Q81.
Working set → number of frames = ?
A) Depends on process locality
B) Fixed
C) Page size
D) TLB size
Answer: A
Solution:
Working set → frames allocated based on recently used pages.
Q82.
LRU uses:
A) Counters or stack
B) FIFO queue
C) Random
D) Base + limit
Answer: A
Solution:
Tracks recent use → least recently used replaced.
Q83.
Clock algorithm → page replaced if:
A) Reference bit = 0
B) Most recent
C) Random
D) FIFO
Answer: A
Solution:
Reference bit 0 → page not recently used → replaced.
Q84.
Number of offset bits = log₂(page size). True/False?
A) True
B) False
Answer: A
Solution:
Offset bits = log₂(page size in bytes).
Q85.
Page table stores:
A) Frame numbers
B) Segment base
C) TLB entries
D) Offset
Answer: A
Solution:
Page → frame mapping.
Q86.
Demand paging → pages loaded:
A) Initially
B) On demand
C) Sequentially
D) Random
Answer: B
Solution:
Pages loaded only when referenced.
Q87.
Thrashing occurs when:
A) Too few frames allocated
B) Page fault rate high
C) CPU idle time increases
D) All
Answer: D
Solution:
Thrashing → high page faults → CPU idle → performance drops.
Q88.
Process = 48 KB, page = 4 KB → pages = ?
A) 11
B) 12
C) 13
D) 14
Answer: B
Solution:
Pages = ceil(48/4)=12 → 12 pages.
Q89.
Optimal page replacement → page replaced = ?
A) Used furthest in future
B) Least recently used
C) FIFO
D) Random
Answer: A
Solution:
Future knowledge → minimum page faults.
Q90.
Internal fragmentation eliminated by:
A) Paging
B) Segmentation
C) Contiguous allocation
D) None
Answer: D
Solution:
Paging reduces external fragmentation, internal may remain.
Q91.
External fragmentation eliminated by:
A) Paging
B) Segmentation
C) Both
D) None
Answer: A
Solution:
Paging → fixed-size frames → no external holes.
Q92.
Segment table stores:
A) Base & limit
B) Frame numbers
C) Offset
D) TLB entries
Answer: A
Solution:
Segment → base + limit → logical → physical mapping.
Q93.
Page fault handling involves:
A) Load page
B) Update page table
C) Resume process
D) All
Answer: D
Solution:
All steps performed → page fault handled.
Q94.
Page table lookup + memory → TLB hit → EMAT = ?
A) Memory access time
B) Memory + TLB
C) Disk access
D) Infinite
Answer: B
Solution:
TLB + memory access.
Q95.
Process = 55 KB, page = 8 KB → pages = ?
A) 6
B) 7
C) 8
D) 9
Answer: B
Solution:
Pages = ceil(55/8)=6.875 → 7 pages.
Q96.
FIFO replacement suffers
from:
A) Belady’s anomaly
B) Thrashing
C) Internal fragmentation
D) None
Answer: A
Solution:
FIFO → page faults may increase with frames → anomaly.
Q97.
Clock algorithm approximates:
A) LRU
B) FIFO
C) Optimal
D) Random
Answer: A
Solution:
Reference bit → approximates LRU.
Q98.
Working set → prevents:
A) Thrashing
B) Page fault
C) Fragmentation
D) Random replacement
Answer: A
Solution:
Ensures enough frames → prevents thrashing.
Q99.
Page replacement occurs when:
A) Free frame exists
B) Page absent + no free frame
C) Page present
D) Random
Answer: B
Solution:
No free frame → replacement required.
Q100.
Page fault occurs if:
A) Page present
B) Page absent
C) TLB hit
D) Reference bit = 1
Answer: B
Solution:
Page fault → page not in memory.
About the Author
