The document discusses paging and segmentation as memory management techniques. Paging allows a process's physical address space to be non-contiguous, organizing memory into pages and frames, while segmentation manages logical entities in a program as units. It also explores the combination of segmentation with paging and its implications for memory allocation and protection.

1. Presented By:
MAYANK SETH
MCA/25002/18

2. CONTENTS
 Meaning of paging
 Meaning of segmentation
 Paging using segmentation

3. PAGING
 Paging is a memory management technique that
permits the physical address space of a process to
be non-contiguous.
 In the logical view, the address space of a process
consists of a linear arrangement of PAGES.
 Each page has s bytes in it, where s is a power of
2.
 The physical memory is divided into fixed block
called FRAMES.
 Size of page = size of frame.

4. PAGING HARDWARE
 The hardware partitions memory into areas called
page frames
 page frames in memory are numbered from 0.
 At any moment, some page frames are allocated to
pages of processes, while others are free.
 The kernel maintains a list called the free frames
list to note the frame numbers of free page frames.
 While loading a process for execution, the kernel
consults the free frames list and allocates a free
page frame to each page of the process.

5.  The MMU decomposes a logical address into the
pair (pi , bi ), where pi is the page number and bi is
the byte number within page pi .
 To facilitate address translation, the kernel
constructs a page table (PT) for each process.
 The page table has an entry for each page of the
process, which indicates the page frame allocated to
the page.
 While performing address translation for a logical
address (pi , bi), the MMU uses the page number pi
to index the page table of the process, obtains the
frame number of the page frame allocated to pi ,and
computes the effective memory address.

6. ADDRESS TRANSLATION IN PAGING
 Page address is called logical address and
represented by page number and the offset.
 Logical Address = Page number + page offset.
 Frame address is called physical address and
represented by a frame number and the offset.
 Physical Address = Frame number + page offset

8. ADVANTAGES AND DISADVANTAGES OF PAGING
Paging is simple to implement and
assumed as an efficient memory
management technique.
Due to equal size of the pages and
frames, swapping becomes very easy.
Page table requires extra memory space,
so may not be good for a system having
small RAM.

9. SEGMENTATION
 A segment is a logical entity in a program, e.g., a
function, a data structure, or an object.
 Hence it is meaningful to manage it as a unit—load
it into memory for execution or share it with other
programs.
 In the logical view, a process consists of a
collection of segments.
 In the physical view, segments of a process exist in
nonadjacent areas of memory.

10.  For example:A process Q consists of five logical entities
with the symbolic names main, database, search, update,
and stack.
 While coding the program, the programmer declares these
five as segments in Q.
 This information is used by the compiler or assembler to
generate logical addresses while translating the program.

11.  The figure shows how the kernel handles process Q.
 The left part of the figure shows the logical view of process
Q.
 To facilitate address translation, the kernel constructs a
segment table for Q.
 Each entry in the table shows the size of a segment and the
address of the memory area allocated to it.
 The MMU uses the segment table to perform address
translation.
 Memory allocation for each segment is performed as in the
contiguous memory allocation model.
 The kernel keeps a free list of memory areas.
 While loading a process, it searches through this list to
perform first-fit or best-fit allocation to each segment of the
process.

12. SEGMENTATION WITH PAGING
 In this approach, each segment in a program is
paged separately.
 Accordingly, an integral number of pages is
allocated to each segment.
 A page table is constructed for each segment, and
the address of the page table is kept in the
segment’s entry in the segment table.

13.  Figure shows processQ in a system using segmentation
with paging.
 Each segment is paged independently, so internal
fragmentation exists in the last page of each segment.
 Each segment table entry now contains the address of the
page table of the segment.
 The size field in a segment’s entry is used to facilitate a
bound check for memory protection.