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ASCII is a 7-level (later: 8-level) binary character-encoding scheme,
derived from the older 5-level
ITA2 standard
(also known as Murray code or
Baudot).
ASCII is the abbreviation of
American Standard Code for Information Interchange.
The standard defines the 128 codes that are possible with 7 bits, all based
on the English (Latin) alphabet. As there are a number of small variations
in ASCII between different countries,
the common standard is often referred to as
US-ASCII.
Compared to the 5-level ITA2 standard (Baudot),
where the characters are
sorted in such a way that they cause minimum (mechanical)
stress on the equipment, characters in the ASCII
table are sorted in the logical order of the alphabet. The first ASCII
standard was published in 1963, with a major revision in 1967.
The most recent update was published in 1986.
ASCII is commonly used by computers for storing programs (software)
and information (data). It has also been the major encoding scheme on the
internet, until it was surpassed by UTF-8 in 2007.
The initial ASCII standard was published when the first computers
entered the stage. These computers used 7-level punched paper tape for
storing their programs and the holes were punched according to the
ASCII scheme. Later, when data was stored in the more convenient 8-bit
pattern, 8-level punched tape was introduced. It allowed 256 characters,
of which the first 128 were defined by the ASCII standard. The extra bit
allowed the introduction of a parity bit (used for error checking),
but could also be used for adding another 128 characters.
Many different encoding schemes for 8-bit exist, but the majority of them
uses ASCII to define the lower 128 characters. The upper half
(sometimes referred to as the 'top-bit-set characters') are often used
for language-dependent encodings, such as ISO-8859-1 (Latin1) and
its Microsoft variant Windows-1252.
The definition of the standard first 128 characters is given below.
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Hex
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0
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1
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2
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3
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4
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5
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6
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7
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8
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9
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A
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B
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C
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D
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E
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F
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0
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NUL
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SOH
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STX
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ETX
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EOT
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ENQ
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ACK
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BEL
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BS
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HT
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LF
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VT
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FF
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CR
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SO
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SI
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1
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DLE
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DC1
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DC2
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DC3
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DC4
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NAK
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SYN
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ETB
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CAN
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EM
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SUB
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ESC
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FS
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GS
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RS
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US
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2
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SP
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!
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"
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#
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$
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%
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&
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'
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(
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)
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*
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+
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,
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-
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.
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/
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3
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0
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1
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2
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3
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4
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5
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6
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7
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8
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9
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:
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;
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<
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=
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>
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?
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4
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@
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A
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B
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C
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D
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E
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F
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G
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H
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I
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J
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K
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L
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M
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N
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O
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5
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P
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Q
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R
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S
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T
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U
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V
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W
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X
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Y
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Z
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[
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\
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]
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^
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_
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6
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`
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a
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b
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c
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d
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e
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f
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g
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h
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i
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j
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k
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l
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m
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n
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o
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7
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p
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q
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r
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s
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t
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u
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v
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w
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x
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y
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z
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{
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}
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~
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DEL
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The first 32 characters are unprintable. They are known as the control
characters and were mainly used for text formatting on teleprinters and
on the first generations of video terminals. Character 127 is also a
special code. It is used to delete a character which, in 7-level paper
tape, was done by punching 7 holes. Control characters are often
written as ^@ (NUL), ^A (SOH), ^B (STX), etc.
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#
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Hex
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Binary
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Char
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Name
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Description
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0
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00
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0000 0000
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^@
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NUL
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Null character (nothing)
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1
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01
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0000 0001
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^A
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SOH
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Start of header
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2
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02
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0000 0010
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^B
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STX
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Start of text
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3
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03
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0000 0011
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^C
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ETX
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End of text
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4
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04
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0000 0100
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^D
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EOT
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End of transmission
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5
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05
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0000 0101
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^E
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ENQ
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Enquiry
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6
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06
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0000 0110
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^F
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ACK
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Acknowlegment
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7
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07
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0000 0111
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^G
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BEL
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Bell (acoustic signal)
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8
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08
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0000 1000
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^H
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BS
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Backspace
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9
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09
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0000 1001
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^I
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HT
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Horizontal Tab
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10
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0A
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0000 1010
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^J
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LF
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Line feed
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11
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0B
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0000 1011
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^K
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VT
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Vertical Tab
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12
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0C
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0000 1100
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^L
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FF
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Form feed (clear screen)
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13
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0D
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0000 1101
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^M
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CR
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Carriage return (enter)
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14
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0E
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0000 1110
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^N
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SO
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Shift Out
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15
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0F
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0000 1111
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^O
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SI
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Shift In
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16
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10
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0001 0000
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^P
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DLE
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Data Link Escape
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17
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11
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0001 0001
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^Q
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DC1
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Device Control 1 (XON)
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18
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12
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0001 0010
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^R
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DC2
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Device Control 2
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19
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13
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0001 0011
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^S
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DC3
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Device Control 3 (XOFF)
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20
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14
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00010100
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^T
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DC4
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Device Control 4
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21
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15
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0001 0101
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^U
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NAK
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Negative Acknowledgment
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22
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16
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0001 0110
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^V
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SYN
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Synchronous idle
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23
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17
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0001 0111
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^W
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ETB
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End of Transmission Block
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24
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18
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0001 1000
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^X
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CAN
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Cancel
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25
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19
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0001 1001
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^Y
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EM
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End of Medium
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26
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1A
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0001 1010
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^Z
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SUB
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Substitute (also: End of File, EOF)
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27
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1B
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0001 1011
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^[
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ESC
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Escape
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28
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1C
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0001 1100
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^\
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FS
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File Separator
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29
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1D
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0001 1101
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^]
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GS
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Group Separator
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30
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1E
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0001 1110
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^^
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RS
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Record Separator
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31
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1F
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0001 1111
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^_
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US
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Unit Separator
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32
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20
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0010 0000
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SP
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SPACE character (printable)
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127
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7F
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0111 1111
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^?
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DEL
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Delete
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© Crypto Museum. Created: Thursday 21 May 2015. Last changed: Friday, 23 February 2018 - 22:30 CET.
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