Memory management techniques involve paging and segmentation. Paging divides memory into fixed-size blocks called frames and logical memory into same-sized blocks called pages. Segmentation divides memory into variable-sized blocks called segments. Paging uses a page table to map logical to physical addresses while segmentation uses a segment table containing the base and limit of each segment. Both techniques allocate and track memory to optimize performance but paging causes internal fragmentation while segmentation causes external fragmentation.

1. • Memory management is the crucial process of
efficiently allocating and organizing computer
memory resources to enable smooth and reliable
operation of software applications.
• It involves tasks such as allocation, DE allocation,
and tracking of memory to optimize system
performance and prevent memory-related issues.
Proper memory management is essential for the
stability and responsiveness of
computer systems.
• It is done through paging and segmentation.

2. • Two fundamental concepts that lie at the core of this
subject are paging and segmentation. These are the
building blocks upon which modern operating systems
and computer architectures are constructed.
• In our quest to understand the dynamic and ever-
evolving field of computer science, it is essential to
grasp the significance of these concepts. Paging and
segmentation serve as vital tools in managing memory
effectively, allowing us to run multiple applications
simultaneously, ensuring data security, and optimizing
system performance.

3. Dynamic Storage-Allocation Problem
• First-fit: Allocate the first hole that is big enough
• Best-fit: Allocate the smallest hole that is big enough; must
search entire list, unless ordered by size
– Produces the smallest leftover hole
• Worst-fit: Allocate the largest hole; must also search entire list
– Produces the largest leftover hole
How to satisfy a request of size n from a list of free holes?
First-fit and best-fit better than worst-fit in terms of speed and
storage utilization

4. Paging
In Operating Systems, Paging is a storage mechanism
used to retrieve processes from the secondary storage
into the main memory in the form of pages.
• Divide physical memory into fixed-sized blocks called
frames
• Divide logical memory into blocks of same size called
pages
• Keep track of all free frames
• To run a program of size N pages, need to find N free
frames and load program
• Set up a page table to translate logical to physical
addresses

5. Address Translation Scheme
• Address generated by CPU is divided into:
– Page number (p) – used as an index into a page table which
contains base address of each page in physical memory
– Page offset (d) – combined with base address to define the
physical memory address that is sent to the memory unit
page number page offset
p d
m -n n

6. Paging Hardware

8. Paging Model of Logical and Physical Memory

9. Pros and cons
pros
• Easy to use memory management algorithm
• No need for external Fragmentation
• Swapping is easy between equal-sized pages and page
frames.
cons
• Here, are drawback/ cons of Paging:
• May cause Internal fragmentation
• Page tables consume additonal memory.
• Multi-level paging may lead to memory reference
overhead.

10. Segmentation
In Operating Systems, Segmentation is a memory management
technique in which the memory is divided into the variable size parts.
Each part is known as a segment which can be allocated to a process.
The details about each segment are stored in a table called a
segment table.
Segment table contains mainly two information about segment:
• Base: It is the base address of the segment
• Limit: It is the length of the segment.
In segmentation we divides the process into the segments. Each
segment contains the same type of functions.
• such as the main function can be included in one segment and the
library functions can be included in the other segment.

11. Logical View of Segmentation
1
3
2
4
1
4
2
3
user space physical memory space

12. Translation of Logical address into
physical address by segment table
• Logical address consists of a two tuple:
<segment-number or base, offset or limit>,
• Segment-table base register (STBR) points to the segment table’s
location in memory
• Segment-table length register (STLR) indicates number of
segments used by a program;
segment number s is legal if s < STLR

13. Segmentation Hardware

14. Segmentation Hardware

15. Pros and cons
pros
• No internal fragmentation
• Average Segment Size is larger than the actual page size.
• Less overhead
• It is easier to relocate segments than entire address space.
• The segment table is of lesser size as compared to the page
table in paging.
cons
• It can have external fragmentation.
• it is difficult to allocate contiguous memory to variable
sized partition.
• Costly memory management algorithms

16. Comparison
Parameters Paging Segmentation
Individual Memory In Paging, we break a
process address space into
blocks known as pages.
In the case of Segmentation,
we break a process address
space into blocks known as
sections.
Memory Size The pages are blocks of
fixed size.
The sections are blocks of
varying sizes.
Accountability The OS divides the available
memory into individual
pages.
The compiler mainly
calculates the size of
individual segments, their
actual address as well as
virtual address.
Speed This technique is
comparatively much faster
in accessing memory.
This technique is
comparatively much slower
in accessing memory than
Paging.

17. Comparison
Size The available memory
determines the individual
page sizes.
The user determines the
individual segment sizes.
Fragmentation The Paging technique may
underutilize some of the
pages- thus leading to
internal fragmentation.
The Segmentation
technique may not use
some of the memory blocks
at all. Thus, it may lead to
external fragmentation.
Logical Address A logical address divides
into page offset and page
number in the case of
Paging.
A logical address divides
into section offset and
section number in the case
of Segmentation.
Data Storage In the case of Paging, the
page table leads to the
storage of the page data.
In the case of Segmentation,
the segmentation table
leads to the storage of the
segmentation data.