Logical addresses are generated by the CPU while physical addresses are seen by memory. The MMU maps virtual addresses to physical addresses using a relocation register. Swapping involves temporarily swapping processes between memory and disk when their time slice expires to allow multitasking.

1. Storage Management
• Logical vs Physical address
• MMU, Swapping
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2. HOME PREVIOUS TOPIC NEXT
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CPP TUTORIALS
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3. Recap
In the last class, you have learnt
• Dynamic linking
- advantages and disadvantages
• Overlays
advantages and disadvantages
-
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4. Objectives
On completion of this class, you will be able to
know
• Logical and Physical addresses
• MMU
• Swapping
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5. Logical Vs Physical address
Logical address
• Address generated by the CPU
Physical address
• Address seen by the memory unit i.e. the one
loaded into memory- address register
Compile –time and Load time address binding
methods generate same logical address and
physical address
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6. Logical Vs Physical address
• Execution time address binding scheme results
in different logical and physical addresses
• Address generated by CPU at execution is
referred as Virtual address
• Logical address space is the set of all logical
addresses generated by program is a logical
address space
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7. Memory Map Unit (MMU)
• MMU is a hardware device
• Maps virtual address to physical address at run
time
• A simple MMU scheme consists relocation register
• A relocation register is a base register
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8. Relocation Register
Base Register
BA
Logical Physical
CPU Address Address
Instruction + Memory
MA MA+BA
Address
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9. Memory Map Unit (MMU)
• Address generated by the CPU are added to
relocation register as shown in previous slide
• Physical address = logical address + contents
of relocation register
• This process is called Dynamic relocation
• The user program deals with logical addresses;
– it never sees the real physical addresses
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10. Memory Map Unit
• Example 1:
Logical address = 346
Relocation register = 14,000
Physical address = 346+14000
= 14346
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11. Dynamic relocation ( MMU )
Example 1
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12. Dynamic relocation ( MMU )
Example 2
Relocation
register
Logical 14000 Physical
address address Memory
CPU +
1800 15800
MMU
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13. Swapping
• A process needs to be in memory to be
executed
• A process can be swapped temporarily out of
memory to a backing store
• Then brought back into memory for continued
execution as shown in next slide
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14. Schematic View of Swapping
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15. Swapping
Backing store
– Fast disk large enough to accommodate copies of all
memory images for all users
– Must provide direct access to these memory images
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16. Swapping
• In Multiprogramming environment and round-
robin CPU scheduling
• When time quantum expires
– the memory manager will swap-out the process to
backing store
– and swap-in another process to the memory space
occupied by the swapped-out process
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17. Swapping
• This process continues until all the processes
are executed
• The memory manager swaps the processes
fast enough
• All ways one process is present in memory
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18. 18

19. Swapping
Priority based scheduling
• Another variant of swapping policy
• Higher priority process is swapped-in and lower
priority swapped-out
• Here the variant used is
– roll-in and roll-out
• Example for Priority based scheduling in next
slides
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20. Swapping
Disk
Monitor
User
Partition
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21. Swapping (contd.)
Disk
Monitor
User
Partition
User 1
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22. Swapping (contd.)
Disk
Monitor
User
Partition
User 1 User 1
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23. Swapping (contd.)
Disk
Monitor
User
Partition
User 1
User 1
User 2
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24. Swapping (contd.)
Disk
Monitor
User
Partition
User 1
User 2
User 2
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25. Swapping (contd.)
Disk
Monitor
User
Partition
User 1
User 2
User 2
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26. Swapping (contd.)
Disk
Monitor
User
Partition
User 1
User 1
User 2
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27. Swapping
• Major part of swap time is transfer time
• Total transfer time is directly proportional to the
amount of memory swapped
• Modified versions of swapping are found on
many systems, i.e., UNIX, Linux, and Windows
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28. Summary
In this class, you have learnt
• Logical and physical addresses
• MMU
• Swapping
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29. Frequently Asked Questions
• Write the differences between logical and
physical address space
• Define logical, virtual and physical addresses
• Draw and explain the basic dynamic
relocation unit (MMU)
• Explain the concept of swapping
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30. Quiz
1. Address seen by the memory unit
a) Logical
b) Physical
c) Virtual
d) None
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31. Quiz
2. Address generated by the CPU at compile
and load time
a) Logical
b) Physical
c) Virtual
d) None
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32. Quiz
3. Address generated by the CPU at execution time
a) Logical
b) Physical
c) Virtual
d) None
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33. Quiz
4. A relocation register is a ______register
a) Base
b) Limit
c) Offset
d) None
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34. Quiz
5. For ___________scheduling when time quantum
expires the memory manager will swap-out the
process to backing store
a) Round robin
b) Priority
c) FIFO
d) None
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35. Other subject materials
• Web designing
• Micro processors
• C++ tutorials
• java
home

36. Quiz
6. Another variant of swapping policy-
a) Priority
b) Round robin
c) FIFO
d) None
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37. Quiz
7. Total transfer time is directly proportional to the
amount of memory swapped
a) True
b) False
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