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• Multiple partition allocation
Storage Management
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Recap
In the last class, you have learnt:
Single partition allocation
Hard ware support for relocation and limit
register
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Objectives
On completion of this class, you will be able to
know
Multiple partition allocation
Allocation of memory
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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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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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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
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 8
Multiple Partition AllocationJob queue
Process Memory Time
P1 600 K 10
P2 1000 K 5
P3 300 K 20
P4 700 K 8
P5 500 K 15
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0 K
400 k
2560 k
OS
2160 K
OS
P1
P2
P3
0 K
400 k
1000 k
2000 k
2300 k
2560 k
P2 Terminates
Allocate P4 P1 TerminatesP5 Allocated
OS
P1
P2
P3
0 K
400 k
1000 k
2000 k
2300 k
2560 k
P1
OS
P4
1700 k
P3
0 K
400 k
1000 k
2000 k
2300 k
2560 k
OS
P4
P3
1700 k
0 K
400 k
1000 k
2000 k
2300 k
2560 k
OS
P4
P3
P5
900 k1000 k
1700 k
0 K
400 k
2000 k
2300 k
2560 k
Indicates a Hole
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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
used
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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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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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Frequently Asked Questions
1. Explain about Multiple Partition Allocation
2. Explain how to allocate memory to a new
process
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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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2. Allocate smallest hole that's big enough
a) First fit
b) Best fit
c) Worst fit
d) None
Quiz
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Quiz
3. Allocate largest hole
a) First fit
b) Best fit
c) Worst fit
d) None
Other subject materials
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home
18
Quiz
4. Block of available memory
a) Hole
b) Byte
c) Word
d) None
