The document discusses multiple partition allocation in storage management. It covers maintaining information about allocated and free partitions in a memory table. When a new process arrives, it is allocated memory from the first hole large enough to accommodate it, using approaches like first-fit, best-fit, or worst-fit allocation. The best-fit approach allocates from the smallest hole that is big enough, while worst-fit allocates from the largest hole.

1. Storage Management
• Multiple partition allocation
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2. HOME PREVIOUS TOPIC NEXT
PREVIOUS QUESTION PAPERS FOR OS
CPP TUTORIALS
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3. Recap
In the last class, you have learnt:
 Single partition allocation
 Hard ware support for relocation and limit
register
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4. Objectives
On completion of this class, you will be able to
know
 Multiple partition allocation
 Allocation of memory
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5. Multiple Partition Allocation
Job scheduling
• Must take into account who wants to run, the memory
needs, and partition availability
• This is a combination of short / medium term scheduling
Sequence of events:
• In an empty memory slot, load a program
• It can compete for CPU time
• Upon job completion, the partition becomes available
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6. Multiple Partition Allocation
Hole
 Block of available memory;
 Holes of various size are scattered throughout
memory
Dynamic storage
 When a process arrives, it is allocated memory
from a hole large enough to accommodate it
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7. Multiple Partition Allocation
• Operating system maintains information about:
• allocated partitions ( holes )
• free partitions ( holes )
• Operating System maintains a table of this
memory
• Space is allocated based on this table
• Adjacent free spaces merged to get largest holes
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8. Multiple Partition Allocation
• Consider an example consisting of 5 processes
from P1 to P5
• These process occupy some space in memory
and corresponding burst times for their execution
as shown in the table in next slide
• Sequence of allocation of these multiple
processes in to the memory capacity of 2160K are
shown in the next slide
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9. Multiple Partition Allocation
Job queue
Indicates a Hole
Process Memory Time
0K 0K 0K 0K 0K
P1 600 K 10
OS OS OS OS OS
P2 1000 K 5
400 k 400 k 400 k 400 k 400 k
P3 300 K 20
P1 P5
P4 700 K 8 P1 P1
P5 500 K 15 900 k
1000 k 1000 k 1000 k 1000 k 1000 k
0K
P2 P4
OS P2 Allocate P4 P1 Terminates
P4 P5 Allocated P4
P2 Terminates
400 k 1700 k 1700 k 1700 k
2000 k 2000 k 2000 k 2000 k 2000 k
2160 K P3 P3 P3 P3 P3
2300 k 2300 k 2300 k 2300 k 2300 k
2560 k 2560 k 2560 k 2560 k 2560 k
2560 k
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10. Memory Allocation
How to allocate memory to a new process?
 First fit
- Allocate the first hole that's big enough
–Search can start at the beginning
–Creates average size holes
 Best fit
-Allocate smallest hole that's big enough
–Must search entire list, unless ordered by size
–Produces the smallest leftover hole which cannot be
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11. Memory Allocation
• Worst fit
– Allocate largest hole
– Must search the entire list, unless sorted by size
– Gets rid of large holes making it difficult to run large
programs
• First-fit and best-fit better than worst-fit in terms
of speed and storage utilization
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12. Summary
In this class, you have learnt
 Multiple Partition Allocation
• Operating system maintains information about:
– Allocated partitions ( holes )
– Free partitions ( holes )
• Operating System maintains a table of this memory
 Allocation of Memory
 First Fit
 Best Fit
 Worst Fit
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13. Frequently Asked Questions
1. Explain about Multiple Partition Allocation
2. Explain how to allocate memory to a new
process
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14. Quiz
1. Allocate the first hole that's big enough
a) First fit
b) Best fit
c) Worst fit
d) None
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15. Quiz
2. Allocate smallest hole that's big enough
a) First fit
b) Best fit
c) Worst fit
d) None
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16. Quiz
3. Allocate largest hole
a) First fit
b) Best fit
c) Worst fit
d) None
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17. Other subject materials
• Web designing
• Micro processors
• C++ tutorials
• java
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18. Quiz
4. Block of available memory
a) Hole
b) Byte
c) Word
d) None
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