This document summarizes a lecture on memory management techniques. It discusses paging and segmentation. With paging, memory is divided into equal fixed-size pages and processes are divided into pages of the same size. A page table maps logical page numbers to physical frame numbers. Segmentation divides a process into variable-length segments. Logical addresses contain a segment number and offset. The lecture compares paging and segmentation and their address translation mechanisms.

1. Chapter (7)
Memory Management
Dr. Hnin Lai Nyo
Lecturer
Faculty of Computer Science

2. Lecture Contents
 Lecture 1: Memory management requirements
 Lecture 2: Memory Partitioning Techniques Part I
 Lecture 3: Memory Partitioning Techniques Part II
 Lecture 4: Paging and Segmentation
FACULTY OF COMPUTER SCIENCE, UNIVERSITY OF COMPUTER STUDIES

3. Lecture 4: Paging and Segmentation
FACULTY OF COMPUTER SCIENCE, UNIVERSITY OF COMPUTER STUDIES
 Paging
 Segmentation

4. Learning Objectives
FACULTY OF COMPUTER SCIENCE, UNIVERSITY OF COMPUTER STUDIES
 To explain the concept of paging
 To discuss the concept of segmentation.

5. FACULTY OF COMPUTER SCIENCE, UNIVERSITY OF COMPUTER STUDIES
 Partition memory into equal fixed-size chunks that are relatively small.
 Process is also divided into small fixed-size chunks of the same size.
 Page: a chunk of a process.
 Frame: available chunks of memory.
Paging

6. FACULTY OF COMPUTER SCIENCE, UNIVERSITY OF COMPUTER STUDIES
Paging
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Main memory
Frame
number A.0
A.1
A.2
A.3
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Main memory
A.0
A.1
A.2
A.3
B.0
B.1
B.2
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Main memory
A.0
A.1
A.2
A.3
B.0
B.1
B.2
C.0
C.1
C.2
C.3
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Main memory
A.0
A.1
A.2
A.3
C.0
C.1
C.2
C.3
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Main memory
A.0
A.1
A.2
A.3
D.0
D.1
D.2
C.0
C.1
C.2
C.3
D.3
D.4
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Main memory
(a) Fifteen available frames (b) Load process A (c) Load process A
(d) Load process C (e) Swap out B (f) Load process D
Figure 7.9 Assignment
of Process to Free
Frames

7. FACULTY OF COMPUTER SCIENCE, UNIVERSITY OF COMPUTER STUDIES
Paging
Page Table
 It is maintained by the operating system for each process.
 It shows the frame location for each page in the process.
 Processor must know how to access the page table of the current process.
 With the logical address, it is used by processor to produce a physical address.

8. FACULTY OF COMPUTER SCIENCE, UNIVERSITY OF COMPUTER STUDIES
Paging
Figure 7.10 Data Structures for the Example of Figure 7.9 at Time Epoch (f)
0
1
2
3
0
1
2
3
Process A
page table
---
---
---
0
1
2
Process B
page table
7
8
9
10
0
1
2
3
Process C
page table
4
5
6
11
0
1
2
3
12
4
Process D
page table
13
14
Free frame
list
Data Structure Examples

9. FACULTY OF COMPUTER SCIENCE, UNIVERSITY OF COMPUTER STUDIES
Paging
Logical Address
User
process
(2,700
bytes)
Relative address = 1502
0000010111011110
Internal
Fragmentation
478
Page
1
Page
2
Page
0
Logical address = Page# = 1,
Offset = 478
0000010111011110
752
Segment
1
1,950
bytes
Segment
0
750
bytes
Logical address =
Segment# = 1, Offset = 752
0001001011110000
(a) Partitioning
(b) Paging (page size=1K)
(c) Segmentation
Figure 7.11 Logical Adresses

10. FACULTY OF COMPUTER SCIENCE, UNIVERSITY OF COMPUTER STUDIES
Paging
Figure 7.12 Examples of Logical-to-Physical Address Translation

11. FACULTY OF COMPUTER SCIENCE, UNIVERSITY OF COMPUTER STUDIES
Segmentation
 A program can be subdivided into segments
 may vary in length
 there is a maximum length
 Addressing consists of two parts:
 segment number
 an offset
 Similar to dynamic partitioning.
 Eliminates internal fragmentation.

12. FACULTY OF COMPUTER SCIENCE, UNIVERSITY OF COMPUTER STUDIES
Segmentation
Figure 7.12 Examples of Logical-to-Physical Address Translation

13. FACULTY OF COMPUTER SCIENCE, UNIVERSITY OF COMPUTER STUDIES
Segmentation
Simple segmentation and Paging comparison
 Segmentation requires more complicated hardware for address translation.
 Segmentation suffers from external fragmentation.
 Paging only yields a small internal fragmentation.
 Segmentation is visible to the programmer whereas paging is transparent.

14. FACULTY OF COMPUTER SCIENCE, UNIVERSITY OF COMPUTER STUDIES
Summary
In this lecture, you learned about
 The basic tools of memory management that are paging and segmentation.
 Possible combination of segmentation and paging in a single memory management
scheme.

15. Learning Outcomes
FACULTY OF COMPUTER SCIENCE, UNIVERSITY OF COMPUTER STUDIES
After the end of the lecture, the students will be able to:
 Understand the concepts of paging with address translation.
 Know the difference between paging and segmentation techniques and how to
translate the logical address into the physical address.

16. References
FACULTY OF COMPUTER SCIENCE, UNIVERSITY OF COMPUTER STUDIES
1. “Operating Systems, internal and Design Principles” by William Stallings, 7th
Edition, ISBN 13: 978-13-230998-1.