Memory Organization in Computers
undefined
MEMORY
ORGANIZATION
1
MEMORY
UNIT
2
an
essential
component in
any
general
purpose
computer
since
it
is
needed
to
store
programs
and
data.
memory
unit
that
communicates
directly
with
the
CPU
=
main
memory
devices
that
provide
backup
storage
=
auxiliary
memory.
Auxiliary
memory
devices are
used
to
store
system
programs,
large
data
files
and
other
backup
information.
Only
programs
and
data
currently
needed
by
the
processor
reside
in
main
memory.
All
other
information
is
stored
in
main
memory
and
transferred
to
main
memory
when
needed.
3
M
e
m
o
r
y
U
n
i
t
C
a
c
h
e
M
e
m
o
r
y
•
Memory
that
lies
in
between
main
memory
and
CPU
Holds those
parts
of
the
program
and
data
that
are
most
heavily
used
•
increases
the
overall
processing
speed
of
the
computer
by
providing
frequently
required
data
to
the
CPU
at
a
faster
speed.
4
M
a
i
n
M
e
m
o
r
y
•
Memory
unit
that
communicates
directly
with
CPU
•
Programs
and
data
currently
needed
by
the
processor
reside
here
•
Also
known
as
primary
memory
•
RAM
and
ROM
5
A
u
x
i
l
i
a
r
y
M
e
m
o
r
y
•
Made
of
devices
that
provide
backup
storage
•
Magnetic
tapes,
Magnetic
disks
•
At
the
bottom
of
the
hierarchy
are
the
relatively
slow
magnetic
tapes
used
to
store
removable
files
whereas
at
the
top
level,
magnetic
disks
used
as
backup
storage
6
Sequential
Access
Memory
•
A
class
of
data
storage
device
that
read
their
data
in
sequence
•
Are usually
a
form
of
magnetic
memory
•
Typically
used
for
secondary
storage
in
general-purpose computers
due
to
their
higher
density,
resistance
to
wear
and
non-volatility
•
Eg:
hard
disk,
CD-ROMs,
magnetic
tapes
etc
Random
Access
Memory
•
Is a
form
of
computer
data
storage
•
Allows
stored
data
to
be
accessed
in
any
order
•
Associated
with
volatile
types
of
memory
•
Type:
SRAM
and
DRAM
7
M
e
m
o
r
y
T
y
p
e
s
•
To
obtain
the
highest
possible
access
speed
while
minimizing
the
total
cost
of
the
memory
system
•
Consists
of
all storage
device
in
a
computer
system
(auxiliary,
cache,
main
,
high
speed
registers
and
processing
logic)
M
e
m
o
r
y
H
i
e
r
a
r
c
h
y
8
9
Magnetic
disk
I/O
Processor
Ma
i
n
Memory
CPU
Ca
c
he
Memory
10
Magnetic
tapes
Fig:
Memory
Hierarchy
in
a
Computer
System
MAIN
MEMORY
11
M
a
i
n
m
e
m
o
r
y
12
•
Basic
memory
of
the
computer
•
Temprorary
memory
except
ROM
•
Faster
for
read
write
operation
•
Expensive
internal
memory
so
not
portable.
R
A
M
•
Volatile
memory.
•
Store
the
information
required
during
processing
Two
types
of
random
Static
R
AM
(SRAM)
and
Dynamic
R
AM
(DRAM)
•
Information
is
stored
in
form
of
voltage
•
faster
•
Loses
its
content
after
few
seconds
•
Information
is
stored
in
the
form
of
charge
•
slower
SRAM
•
Does
not
lose
its
content
until
computer
is
turned
off
DRAM
T
Y
P
E
S
O
F
R
A
M
13
•
Permanent
memory
•
Store
the
information
required
for
computer
operations
•
Types
of
ROM
(PROM,EPROM,EEPROM)
R
O
M
14
Boot
Strap
loader
Initial
program
whose
function
is
to
start
the
computer
operating
system
after
the
power
is
turned
on.
and
it
is
stored
in
the
ROM
portion
of
the
main
memory
.
Computer
start
up
:starting
the execution
of
initial
program
after
computer
is
turned
on
Boot
strap
loader
loads
the
portion
of
disk
to
main
memory
and
control
is
then
transferred
to
OS
.
15
•
The
most
common
auxilliary
device used
in the computer
system
is
magnetic
disk
and
magnetic
tape.
•
Store
large
amount
of
data
permanantly.
•
Portable
T
y
p
e
s
o
f
a
u
x
i
l
l
i
a
r
y
m
e
m
o
r
y
Magnetic
disk
Magnetic
tape
A
u
x
i
l
i
a
r
y
m
e
m
o
r
y
(
S
E
C
O
N
D
A
R
Y
M
E
M
O
R
Y
)
16
•
circular
plate
,made
of
metal
or
plastic
coated
with
magnetize
material. High
speed
of
rotation
•
Bits
are
store
in
a
concentric
circle called
tracks.
•
Division
of
tracks
are
called
sectors
.
M
a
g
n
e
t
i
c
d
i
s
k
17
Magnetic
disk
18
Sequential
access
memory
used
for
storing,backup,audio,video
data
etc
.
Highly
reliable
memory.
Slower
for
read
write
operation.
M
a
g
n
e
t
i
c
t
a
p
e
19
Magnetic
tape
20
RAM
AND
ROM
CHIP
21
RAM
AND
ROM
CHIPS
22
RAM
chip:
Used
for
communication
with
the
CPU
if
one
or
more
control
inputs.
requires
7-bit
address
and
an
8-bit
bidirectional
data
bus.
chip
select
(CS)
are
for
enabling
the
chip.
Fig.
RAM
chip
23
when
CS1=1
and
(CS2)’=0,
the
unit
in
operation.
High
impedance
state
indicates
open
circuit.
When
CS1=1
and
(CS2)’=0,
the
memory
is
places
in
a
R/W
mode.
When
the
RD
input
is
enabled,
the
content
of
the
selected
byte
is
placed
into
the
data
bus.
24
ROM
chip
25
A
ROM
chip
is
unidirectional.
26
9
address
lines
to
address
512
bytes.
chip
s
e
lect
C
S
1
=
1
and
(C
S
2
)’
=
0
for
the
unit
to
operate.
Other
w
i
s
e,
the
data
bus
i
n
a
hig
h
-
i
m
ped
a
nce
state.
VIRTUAL
MEMORY
27
Attempts
to
optimize
the
use
of
the
main
memory(the
high
speed
portion) with
the
hard
disk
(the
lower
speed
portion).
Technique
for
using
the
secondary
storage
to
extend
the
apparent
limited
size
of
the
physical
memory beyond
its
physical
size
.
Implemented
since
the
available physical
memory
will
not
be
enough
to
host
all
the
program.
28
Address space
and
Memory
space
An
address
used
by
the
programmer
is
virtual
memory
,
the
set
of
such
address
is
called
address
space.
An
address
in
main
memory
is
location
,the
set
of
such
location
is
called
memory
space.
Example:
consider
main
memory
:32k
words(k=1024)=2^15
and
auxiliary
memory
1024k
words=2^20(to
address
15
bits
of
physical
memory
and
20
bits
of
virtual
memory
is
required)
29
.
30
.
31
In
our
example
we
have
20-bit
address
of
an
instruction
(to
refer
20-bit
virtual
address)
but
physical
memory
addresses
are
specified
with
15-bits.
So
a
table
is
needed
to
map
a
virtual
address
of
20-bits
to
a
physical
address
of
15-bits.
Mapping
is
a
dynamic
operation,
which
means
that
every
address
is
translated
immediately
as
a
word
is
referenced
by
CPU.
32
A
d
d
r
e
s
s
M
a
p
p
i
n
g
u
s
i
n
g
P
a
g
e
s
B
l
o
c
k
s
(
o
r
p
a
g
e
f
r
a
m
e
)
:
B
l
o
c
k
s
a
r
e
t
h
e
g
r
o
u
p
s
o
f
e
q
u
a
l
s
i
z
e
w
h
i
c
h
a
r
e
b
r
o
k
e
n
d
o
w
n
f
r
o
m
p
h
y
s
i
c
a
l
m
e
m
o
r
y
a
n
d
r
a
n
g
e
s
f
r
o
m
6
4
t
o
4
0
9
6
w
o
r
d
s
e
a
c
h
.
P
a
g
e
s
:
r
e
f
e
r
s
t
o
a
p
o
r
t
i
o
n
o
f
s
u
b
d
i
v
i
d
e
d
v
i
r
t
u
a
l
m
e
m
o
r
y
h
a
v
i
n
g
s
a
m
e
s
i
z
e
a
s
b
l
o
c
k
s
i
.
e
.
g
r
o
u
p
s
o
f
a
d
d
r
e
s
s
s
p
a
c
e
.
33
Example:
consider
computer
with
address
space
=
8K
and
memory
space
=
4K.
If
we
spit
both
spaces
into
groups
of
1k
words
we
get
8
pages
and
4
blocks.
blocks.
34
P
a
g
e
R
e
p
l
a
c
e
m
e
n
t
A
virtual memory
system
is
a
combination
of
hardware
and
software
techniques.
A
memory
management
software
system
handles:
Which
page
in
main
memory
should
be
removed
to
make
room for
a
new
page?
When
a
new
page
is
to
be transferred
from
auxiliary
memory
to
main
memory?
35
36
Where
the
page
is
to
be
placed
in
main
memory?
There
are
numerous
page
replacement
algorithms,
two
of
which
are:
1.
First-in
First-out
(FIFO):
replaces
a
page
that
has
been
in
memory
longest
time.
2.
Least
Recently
Used
(LRU):
assumes
that
least
recently
used
page
is
the
better
candidate
for
removal
than
the
least
recently
loaded
page.
37
When
a
page
fault
occurs
in
a
virtual
memory
system,
it
signifies
that
the
page
referenced
by
the
program
is
not
in
main
memory.
A
new
page
is
then
transferred
from
auxiliary
memory
to
main
memory.
If
main
memory
is
full,
it
would
be
necessary
to
remove
a
page
from
a
memory
block
to
make
a
room for
a
new
page.
The
policy
for
choosing
pages
to
remove
is
determined
from
the
replacement
algorithm
that
is
used.
GOAL
:
try
to
remove
the
page
least
likely
to
be
referenced
by
in
the
immediate
future.
Memory
Management
Hardware
38
Introduction
Collection
of
hardware
and
software
procedures
for
managing
various
program.
39
Basic
component of
MMU
Sharing
common
program
by
multiple
user
Protection
of
information
unauthorized
40
Segmented
Page
Mapping
Length
of
each
segment
allowed
to
grow
and
contract
according
need
of
program
execution.
Way
of
specifying
the
length
of
a
segment
by
associating
with
it
a
no.
of
equal sized
page
Consider
diagram
below
41
42
In
above
fig:
Consider
Logical
Address=Segment+page+word
segment
specifies
segment
no.
Page
field
specifies
page
within
the
segment
Word field
specifies
specific
word
within
the
page
43
44
45
Delve into the intricate world of memory organization within computer systems, exploring the vital role of memory units, cache memory, main memory, auxiliary memory, and the memory hierarchy. Learn about the different types of memory, such as sequential access memory and random access memory, and how they contribute to the overall performance and efficiency of a computer. Unravel the complexities of memory systems to enhance your understanding of computing fundamentals.
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Presentation Transcript
2 MEMORY UNIT
Memory Unit 3 an essential component in any general purpose computer sinceit is needed to store programs and data. memory unit that communicates directly with the CPU = main memory devices that provide backup storage = auxiliarymemory. Auxiliary memory devices are used to store system programs, large data files and other backup information. Only programs and data currently needed by the processor reside in main memory. All other information is stored in main memory and transferred to main memory when needed.
CacheMemory 4 Memory that lies in between main memory and CPU Holds those parts of the program and data that are most heavily used increases the overall processing speed of the computer by providing frequently required data to the CPU at a fasterspeed.
5 Main Memory Memory unit that communicates directly with CPU Programs and data currently needed by the processor reside here Also known as primary memory RAM and ROM
6 Auxiliary Memory Made of devices that provide backup storage Magnetic tapes, Magnetic disks At the bottom of the hierarchy are the relatively slow magnetic tapes used to store removable files whereas at the top level, magnetic disks used as backup storage
Memory Types 7 Sequential Access Memory A class of data storage device that read their data in sequence Are usually a form of magnetic memory Typically used for secondary storage in general-purpose computers due to their higher density, resistance to wear and non-volatility Eg: hard disk, CD-ROMs, magnetic tapes etc Random Access Memory Is a form of computer data storage Allows stored data to be accessed in anyorder Associated with volatile types of memory Type: SRAM and DRAM
Memory Hierarchy 8 To obtain the highest possible access speed while minimizing the total cost of the memory system Consists of all storage device in a computer system (auxiliary, cache, main , high speed registers and processing logic)
10 Magnetic tapes Main Memory I/O Processor Magnetic disk Cache Memory CPU Fig: Memory Hierarchy in a Computer System
11 MAIN MEMORY
Main memory 12 Basic memory of the computer Temprorary memory except ROM Faster for read write operation Expensive internal memory so not portable. RAM Volatile memory. Store the information required during processing Two types of random Static RAM(SRAM) and Dynamic RAM(DRAM)
TYPES OF RAM 13 DRAM SRAM Loses its content after few seconds Does not lose its content until computer is turned off Information is stored in form of voltage Information is stored in the form of charge faster slower
14 ROM Permanent memory Store the information required for computer operations Types of ROM (PROM,EPROM,EEPROM)
Boot Straploader 15 Initial program whose function is to start the computer operating system after the power is turned on. and it is stored in the ROM portion of the main memory. Computer start up :starting the execution of initial program after computer is turned on Boot strap loader loads the portion of disk to main memory and control is then transferred to OS.
Auxiliary memory(SECONDARY MEMORY) 16 The most common auxilliary device used in the computer systemis magnetic disk and magnetic tape. Store large amount of datapermanantly. Portable Types of auxilliary memory Magnetic disk Magnetic tape
Magnetic disk 17 circular plate ,made of metal or plastic coated with magnetize material. High speed of rotation Bits are store in a concentric circle called tracks. Division of tracks are called sectors.
Magnetic tape 19 Sequential access memory used for storing,backup,audio,video data etc . Highly reliable memory. Slower for read write operation.
21 RAM AND ROMCHIP
RAM AND ROMCHIPS 22 RAM chip: Used for communication with the CPU if one or more control inputs. requires 7-bit address and an 8-bit bidirectional data bus. chipselect (CS) are for enabling the chip.
24 when CS1=1 and (CS2) =0, the unit in operation. High impedance state indicates opencircuit. When CS1=1 and (CS2) =0, the memory is places in a R/W mode. When the RD input is enabled, the content of the selected byte is placed intothe data bus.
ROM chip 25
A ROM chip isunidirectional. 26 9 address lines to address 512bytes. chip select CS1=1 and (CS2) =0 for the unit to operate. Otherwise, the data bus in a high-impedance state.
27 VIRTUAL MEMORY
28 Attempts to optimize the use of the main memory(thehigh speed portion) with the hard disk (the lower speedportion). Technique for using the secondary storage to extend the apparent limited size of the physical memory beyond its physical size . Implemented since the available physical memory will not be enough to host all the program.
Address space and Memory space 29 An address used by the programmer is virtual memory , the set of such address is called address space. An address in main memory is location ,the set of such location is called memory space. Example: consider main memory :32k words(k=1024)=2^15 and auxiliary memory 1024k words=2^20(to address 15 bits of physical memory and 20 bits of virtual memory is required)
. 30
. 31 In our example we have 20-bit address of an instruction (to refer 20-bit virtual address) but physical memory addresses are specified with 15-bits. So a table is needed to map a virtual address of 20-bits to a physical address of 15-bits. Mapping is a dynamic operation, which means that every address is translated immediately as a word is referenced by CPU.
Address Mapping using Pages 33 Blocks (or page frame): Blocks are the groups of equal size which are broken down from physical memory and ranges from 64 to 4096wordseach. Pages: refers to a portion of subdivided virtual memory having same size as blocks i.e. groups of address space.
Example: consider computer with address space = 8K and memory space = 4K. 34 If we spit both spaces into groups of 1k words we get 8 pages and 4 blocks. blocks.
35 Page Replacement A virtual memory system is a combination of hardware and software techniques. A memory management software system handles: Which page in main memory should be removed to make room for a new page? When a new page is to be transferred from auxiliarymemory to main memory?
36 Where the page is to be placed in mainmemory? There are numerous page replacement algorithms, two of which are: First-in First-out (FIFO): replaces a page that has been in memory longest time. 2. Least Recently Used (LRU): assumes that least recently used page is the better candidate for removal than the least recently loaded page. 1.
37 When a page fault occurs in a virtual memory system, it signifies that the page referenced by the program is not in main memory. A new page is then transferred from auxiliary memory to main memory. If main memory is full, it would be necessary to remove a page from a memory block to make a room for a new page. The policy for choosing pages to remove is determined from the replacement algorithm that is used. GOAL: try to remove the page least likely to be referencedby in the immediate future.
38 Memory Management Hardware
Introduction 39 Collection of hardware and software procedures for managing various program.
Basic component of MMU 40 Sharing common program by multiple user Protection of information unauthorized
Segmented Page Mapping 41 Length of each segment allowed to grow and contract according need of program execution. Way of specifying the length of a segment by associating with it a no. of equal sized page Consider diagram below
In above fig: Consider Logical Address=Segment+page+word segment specifies segment no. Page field specifies page within the segment Word field specifies specific word within the page 43
