Lecture Slides of Introduction to Information Technology. The lecture slides are based on the book of Brian K. Williams and Stacey C. Sawyers

1. Data Representation in Computers
Instructor: Ch. Bilal Ahmad Khan
Company
LOGO

2. Data Representation in Computers
2

3. Data Representation in Computers
3

4. Data Representation in Computers
4

5. Data Representation in Computers
5

6. Data Forms
 Human communication
Includes language, images and sounds
 Computers
Process and store all forms of data in binary
format
 Conversion to computer-usable
representation using data formats
Define the different ways human data may be
represented, stored and processed by a
computer
6

7. Data conversion and representation
7

8. Common Data Representations
Type of Data
Standard(s)
Alphanumeric
BCD, ASCII, EBCDIC, Unicode
Image (bitmapped)
GIF
Image (object)
PostScript, JPEG, SWF
(Macromedia Flash), SVG
Outline graphics and
fonts
PostScript, TrueType
Sound
WAV, AVI, MP3, MIDI, WMA
Page description
PDF (Adobe Portable Document
Format), HTML, XML
Video and Sound
Quicktime, MPEG-2, MPEG-4,
RealVideo, WMV
(graphical image format)
TIF (tagged image file format)
PNG (portable network graphics)
9

9. Alphanumeric Data
 Groups of data:

Characters: A, B, …, Z and a, b,…, z

Numbers/digits: 0 … 9

Punctuations: !, ;, :, ? etc

Special purpose characters: $, @, #, *, …, &
 Four coding systems /standards to represent above
types:
BCD (Binary-Coded Decimal)
ASCII (American Standard Code for Information Interchange)
EBCDIC (Extended Binary Coded Decimal Interchange Code)
Unicode
10

10. Standard Alphanumeric
Formats
BCD
 ASCII
 EBCDIC
 Unicode

Next 2 slides
11

11. Binary-Coded Decimal
(BCD)

Four bits per digit
Digit
Bit pattern
0
0000
Note: the following 6 bit
patterns are not used:
1
0001
2
0010
1010
1011
1100
1101
1110
1111
3
0011
4
0100
5
0101
6
0110
7
0111
8
1000
9
1001
12

12. BCD: Example

709310 = ? (in BCD)
7
0
9
3
0111
0000
1001
0011
Or
0111000010010011
13

13. Standard Alphanumeric
Formats
BCD
 ASCII
 EBCDIC
 Unicode

Next 13 slides
14

14. ASCII Features




Developed by ANSI (American National Standards Institute)
Defined in ANSI document X3.4-1977
7-bit code
8th bit is unused (or used for a parity bit or to indicate “extended”
character set)
 27 = 128 different codes
 Two general types of codes:
95 are “Printing” codes (displayable on a console)
33 are “Control” codes (control features of the console or
communications channel)
 Represents
Latin alphabet, Arabic numerals, standard punctuation characters
Plus small set of accents and other European special characters (Latin-I
ASCII)
15

15. ASCII Table
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
000
NULL
SOH
STX
ETX
EDT
ENQ
ACK
BEL
BS
HT
LF
VT
FF
CR
SO
SI
001
DLE
DC1
DC2
DC3
DC4
NAK
SYN
ETB
CAN
EM
SUB
ESC
FS
GS
RS
US
010
!
"
#
$
%
&
'
(
)
*
+
,
.
/
011
0
1
2
3
4
5
6
7
8
9
:
;
<
=
>
?
100
@
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
101
P
Q
R
S
T
U
V
W
X
Y
Z
[
]
^
_
110
`
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
111
p
q
r
s
t
u
v
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x
y
z
{
|
}
~
DEL
16

16. ASCII Table
000
001
0000
NULL
DLE
0001
SOH
DC1
0010
STX
DC2
0011
ETX
DC3
0100
EDT
DC4
0101
ENQ
NAK
0110
ACK
SYN
0111
BEL
ETB
1000
BS
CAN
1001
HT
EM
1010
LF
SUB
1011
VT
Least significant ESC
bit
1100
FF
FS
1101
CR
GS
1110
SO
RS
1111
SI
US
010
011
0
!
1
"
2
#
3
Most significant bit
$
4
%
5
&
6
'
7
(
8
)
9
*
:
+
;
,
<
=
.
>
/
?
100
@
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
101
P
Q
R
S
T
U
V
W
X
Y
Z
[
]
^
_
110
`
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
111
p
q
r
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u
v
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x
y
z
{
|
}
~
DEL
17

17. ASCII Table
e.g., ‘a’ = 1100001
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
000
NULL
SOH
STX
ETX
EDT
ENQ
ACK
BEL
BS
HT
LF
VT
FF
CR
SO
SI
001
DLE
DC1
DC2
DC3
DC4
NAK
SYN
ETB
CAN
EM
SUB
ESC
FS
GS
RS
US
010
!
"
#
$
%
&
'
(
)
*
+
,
.
/
011
0
1
2
3
4
5
6
7
8
9
:
;
<
=
>
?
100
@
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
101
P
Q
R
S
T
U
V
W
X
Y
Z
[
]
^
_
110
`
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
111
p
q
r
s
t
u
v
w
x
y
z
{
|
}
~
DEL
18

18. ASCII Table
95 Printing codes
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
000
NULL
SOH
STX
ETX
EDT
ENQ
ACK
BEL
BS
HT
LF
VT
FF
CR
SO
SI
001
DLE
DC1
DC2
DC3
DC4
NAK
SYN
ETB
CAN
EM
SUB
ESC
FS
GS
RS
US
010
!
"
#
$
%
&
'
(
)
*
+
,
.
/
011
0
1
2
3
4
5
6
7
8
9
:
;
<
=
>
?
100
@
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
101
P
Q
R
S
T
U
V
W
X
Y
Z
[
]
^
_
110
`
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
111
p
q
r
s
t
u
v
w
x
y
z
{
|
}
~
DEL
19

19. ASCII Table
33 Control codes
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
000
NULL
SOH
STX
ETX
EDT
ENQ
ACK
BEL
BS
HT
LF
VT
FF
CR
SO
SI
001
DLE
DC1
DC2
DC3
DC4
NAK
SYN
ETB
CAN
EM
SUB
ESC
FS
GS
RS
US
010
!
"
#
$
%
&
'
(
)
*
+
,
.
/
011
0
1
2
3
4
5
6
7
8
9
:
;
<
=
>
?
100
@
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
101
P
Q
R
S
T
U
V
W
X
Y
Z
[
]
^
_
110
`
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
111
p
q
r
s
t
u
v
w
x
y
z
{
|
}
~
DEL
20

20. ASCII Table
Alphabetic codes
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
000
NULL
SOH
STX
ETX
EDT
ENQ
ACK
BEL
BS
HT
LF
VT
FF
CR
SO
SI
001
DLE
DC1
DC2
DC3
DC4
NAK
SYN
ETB
CAN
EM
SUB
ESC
FS
GS
RS
US
010
!
"
#
$
%
&
'
(
)
*
+
,
.
/
011
0
1
2
3
4
5
6
7
8
9
:
;
<
=
>
?
100
@
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
101
P
Q
R
S
T
U
V
W
X
Y
Z
[
]
^
_
110
`
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
111
p
q
r
s
t
u
v
w
x
y
z
{
|
}
~
DEL
21

21. ASCII Table
Numeric codes
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
000
NULL
SOH
STX
ETX
EDT
ENQ
ACK
BEL
BS
HT
LF
VT
FF
CR
SO
SI
001
DLE
DC1
DC2
DC3
DC4
NAK
SYN
ETB
CAN
EM
SUB
ESC
FS
GS
RS
US
010
!
"
#
$
%
&
'
(
)
*
+
,
.
/
011
0
1
2
3
4
5
6
7
8
9
:
;
<
=
>
?
100
@
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
101
P
Q
R
S
T
U
V
W
X
Y
Z
[
]
^
_
110
`
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
111
p
q
r
s
t
u
v
w
x
y
z
{
|
}
~
DEL
22

22. ASCII Table
Punctuation, etc.
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
000
NULL
SOH
STX
ETX
EDT
ENQ
ACK
BEL
BS
HT
LF
VT
FF
CR
SO
SI
001
DLE
DC1
DC2
DC3
DC4
NAK
SYN
ETB
CAN
EM
SUB
ESC
FS
GS
RS
US
010
!
"
#
$
%
&
'
(
)
*
+
,
.
/
011
0
1
2
3
4
5
6
7
8
9
:
;
<
=
>
?
100
@
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
101
P
Q
R
S
T
U
V
W
X
Y
Z
[
]
^
_
110
`
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
111
p
q
r
s
t
u
v
w
x
y
z
{
|
}
~
DEL
23

23. ASCII Table
MSD
LSD
0
1
2
3
4
5
0
NUL
DLE
SP
0
@
P
1
SOH
DC1
!
1
A
Q
a
W
2
STX
DC2
“
2
B
R
b
r
3
ETX
DC3
#
3
C
S
c
s
4
EOT
DC4
$
4
D
T
d
t
5
ENQ
NAK
%
5
E
U
e
u
6
ACJ
SYN
&
6
F
V
f
v
7
BEL
ETB
‘
7
G
W
g
w
8
BS
CAN
(
8
H
X
h
x
9
HT
EM
)
9
I
Y
i
y
A
LF
SUB
*
:
J
Z
j
z
B
VT
ESC
+
;
K
[
k
{
C
FF
FS
,
<
L
l
|
D
CR
GS
-
=
M
]
m
}
E
SO
RS
.
>
N
^
n
~
F
SI
US
/
?
O
_
o
DEL
6
7
p
7416
111 0100
24

24. Example: “Hello, world”
H
e
l
l
o
,
w
o
r
l
d
=
=
=
=
=
=
=
=
=
=
=
=
Binary
1001000
1100101
1101100
1101100
1101111
0101100
0100000
1110111
1100111
1110010
1101100
1100100
=
=
=
=
=
=
=
=
=
=
=
=
Hexadecimal
48
65
6C
6C
6F
2C
20
77
67
72
6C
64
=
=
=
=
=
=
=
=
=
=
=
=
Decimal
72
101
108
108
111
44
32
119
103
114
108
100
25

25. EASCII
28

26. EASCII
29

27. Standard Alphanumeric
Formats
BCD
 ASCII
 EBCDIC
 Unicode

Next 3 slides
30

28. EBCDIC
 8-bit code
ASCII
EBCDIC
Space
2016
4016
 Character codes differ from
ASCII
A
4116
C116
 Conversion software to/from
ASCII available
b
6216
8216
 Developed by IBM for
mainframes computers
 Rarely used today, common in
archival data
31

29. EBCDIC Table
(1 of 2)
32

30. EBCDIC Table
(2 of 2)
33

31. Standard Alphanumeric
Formats
BCD
 ASCII
 EBCDIC
 Unicode

Next 2 slides
34

32. Unicode
 Most common 16-bit form represents 65,536 characters
 EASCII is a subset of Unicode
Values 0 to 255 in Unicode table
 Multilingual: defines codes for
Nearly every character-based alphabet
Chinese, Japanese and Korean alphabets
 Allows software modifications for local-languages
representations
35

33. Two-byte Unicode Assignment Table
36