dsvv

1. Virtual memory
addressing

2. agenda
INTRODUCTION
3
HISTORY
4
USAGE
5
FOUNDER
7
SUMMARY
9

3. introduction
When a user program wants to allocate memory, it asks
the Operating System (OS) to do that by performing a system
call. This way, the OS can properly manage memory among all
the running processes.
Beyond that, the OS implements Virtual Memory with the main
objective of extending memory size by allowing some parts of it
to be temporarily moved into the hard drive.
With this mechanism, a given memory address may not be in the
physical memory. The solution for that is to use virtual
addresses instead of physical addresses
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4. History
• In the 1950s, all larger programs had to contain logic for
managing primary and secondary storage, such as overlaying.
Virtual memory was therefore introduced not only to extend
primary memory, but to make such an extension as easy as
possible for programmers to use.
• To allow for multiprogramming and multitasking, many early
systems divided memory between multiple programs without
virtual memory, such as early models of the PDP-
10 via registers.

5. Virtual memory is an integral part of a
modern computer architecture;
implementations usually require hardware
support, typically in the form of a memory
management unit built into the CPU. While
not necessary, emulators and virtual
machines can employ hardware support to
increase performance of their virtual
memory implementations
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usage

6. Paged virtual memory
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•Page tables
•Paging supervisor
•Pinned paging
•Thrashing
Nearly all current
implementations of
virtual memory
divide a virtual
address
space into pages,
blocks of
contiguous virtual
memory addresses

7. FRITZ-RUDOLF GÜNTSCH
Concept of virtual memory was first
developed by German physicist Fritz-
Rudolf Güntsch at the Technische
Universität Berlin in 1956 in his doctoral
thesis
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8. Early systems..
1.Early systems used drums contemporary systems use disks or solid state memory
1.IBM uses the term virtual storage on mainframe operating systems. This usage runs
from TSS on the 360/67through z/OS on z/Architecture.
1.IBM had previously used the term hypervisor for the 360/65, but that did not involve virtual
memory
1.IBM DOS/VS, OS/VS1 and DOS/VS only supported 2 KB pages.
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9. Summary
Virtual memory is a common
part of most operating
systems on computers
It has become so common
because it provides a big
benefit for users at a very
low cost
Virtual memory makes
application programming
easier by
hiding fragmentation of
physical memory
Program is no longer
constrained by the amount
of physical memory
Benefits of executing a
program that is only
partially in memory

10. thank you
J ABISHEK
22BCA002