ASCII (American Standard Code for Information Interchange)

As you probably know, in its lower level computers can only handle 0s (zeros) and 1s (ones). Using sequences of 0 and 1 a computer can handle numbers in binary format (as explained in document numeral radixes). Nevertheless there is no such evident way to represent letters with 0s and 1s. For this purpose is the ASCII code used.

The ASCII code is a table or list containing all the letters of the alphabet plus a variety of additional characters. In this code, each character is represented by an order number, which is always the same. For example, the ASCII code to represent the capital letter A is always represented by order number 65, which is easily representable using 0s and 1s in binary notation (1000001).

The standard ASCII code defines 128 character codes (from 0 to 127). The first 32 are control codes (non-printable), and the other 96 are representable characters:

*

0

1

2

3

4

5

6

7

8

9

A

B

C

D

E

F

0

NUL

SOH

STX

ETX

EOT

ENQ

ACK

BEL

BS

TAB

LF

VT

FF

CR

SO

SI

1

DLE

DC1

DC2

DC3

DC4

NAK

SYN

ETB

CAN

EM

SUB

ESC

FS

GS

RS

US

2

!

"

#

$

%

&

'

(

)

*

+

,

-

.

/

3

0

1

2

3

4

5

6

7

8

9

:

;

<

=

>

?

4

@

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

5

P

Q

R

S

T

U

V

W

X

Y

Z

[

\

]

^

_

6

`

a

b

c

d

e

f

g

h

i

j

k

l

m

n

o

7

p

q

r

s

t

u

v

w

x

y

z

{

|

}

~

* This panel is organized to be easily read in hexadecimal: row numbers represent the first digit and the column numbers represent the second one. For example, the A character is located at the 4th row and the 1st column, so it would be represented as hexadecimal number 0x41 (65).

In addition to the 128 standard ASCII codes (the ones listed above ranging from 0 to 127), most machines have another 128 extra codes which form what is known as extended ASCII (with ranges from 129 to 255). This extended ASCII character set is platform-dependent, meaning that it may vary from one machine to another, or between operating systems.

The most-used extended ASCII character sets are OEM and ANSI.

The OEM character set is included in all PC-compatible computers as the default character set when the system boots before loading any operating system and under MS-DOS. It includes some foreign signs, some marked characters and also pieces to draw simple panels. Unfortunately it is usually redefined by some regional country-specific configurations to include local symbols.

Here you have an interactive Decimal-Hexadecimal-Octal-ASCII converter (Netscape 3+ or MSIE 4+):

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