VIRTUAL MEMORY

1. UNIT IV
VIRTUAL MEMORY
Mr. C.KARTHIKEYAN,
ASSISTANT PROFESSOR,
ECE , RMKCET

2. VIRTUAL MEMORY
0
1
2
3
.
.
.
0
1
2
PROGRAM ADDRESS SPACE
(4 GB)
RAM (1 GB)
Without Virtual Memory
Program Address = RAM Address
??
If No VM, Crash if
we try to access
more than RAM
than we have

3. OVERLAYS
An approach of using disk storage to augment the main memory

4. OVERLAYS
When more than one program is loaded into memory
overlays cannot operate
without interacting with
the operating system in
order to find out which
portions of memory are
available

5. PAGING
With Virtual Memory
By adding indirection we can solve the issue
Program Address maps to RAM Address
0
1
2
3
.
.
.
PROGRAM ADDRESS SPACE
(4 GB)
Page 0
Page 1
Page 2
RAM (1 GB)
MAP

6. PAGING
Program Address maps to RAM Address
PROGRAM ADDRESS SPACE
(4 GB)
RAM (1 GB)
MAP
Program 0
Program 0
Program 1
Program 1
Program 2
Program 2
Program 3
Program 3
Gives an illusion of unlimited memory
Performance will go down

7. SEGMENTATION
RAM (4 GB)
Program 1
(2 GB)
Program 2
(2 GB)

8. SEGMENTATION
RAM (4 GB)
Program 2
(2 GB)
Program 1
(2 GB)
MAP 1
MAP 2
Program 1
(2 GB)

9. SEGMENTATION
RAM (4 GB)
Program 2
(2 GB)
Program 1
(2 GB)
MAP 1
MAP 2
Fragmentation issue
also encountered
with Segmentation

10. RAM Address Space
Program 2
(2 GB)
Program 1
(2 GB)
MAP 1
MAP 2
Accessing
Address 512
Accessing
Address 512
Improves Security
P1 stores bank balance
at address 512
P2 access address 512
for gaming
Isolates the Programs

11. RAM Address Space
Program 2
(2 GB)
Program 1
(2 GB)
MAP 1
MAP 2
Accessing
Address 512
Accessing
Address 512
SHARED MEMORY