EBCDIC

Extended Binary Coded Decimal Interchange Code[1] (EBCDIC[1]) is an eight-bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems. EBCDIC descended from the code used with punched cards and the corresponding six bit binary-coded decimal code used with most of IBM's computer peripherals of the late 1950s and early 1960s.[2] It is also supported on various non-IBM platforms such as Fujitsu-Siemens' BS2000/OSD, OS-IV, MSP, and MSP-EX, the SDS Sigma series, and Unisys VS/9 and MCP.

History

Punched card with the 1964 EBCDIC character set. Contrast at top enhanced to show the printed characters.

EBCDIC /ˈɛbsᵻdɪk/ was devised in 1963 and 1964 by IBM and was announced with the release of the IBM System/360 line of mainframe computers. It is an eight-bit character encoding, developed separately from the 7-bit ASCII encoding scheme. It was created to extend the existing Binary-Coded Decimal (BCD) Interchange Code, or BCDIC, which itself was devised as an efficient means of encoding the two zone and number punches on punched cards into 6 bits.

While IBM was a chief proponent of the ASCII standardization committee,[3] the company did not have time to prepare ASCII peripherals (such as card punch machines) to ship with its System/360 computers, so the company settled on EBCDIC.[4] The System/360 became wildly successful, together with clones such as RCA Spectra 70, ICL System 4, and Fujitsu FACOM, thus so did EBCDIC.

All IBM mainframe and midrange peripherals and operating systems use EBCDIC as their inherent encoding[5] (with toleration for ASCII, for example, ISPF in z/OS can browse and edit both EBCDIC and ASCII encoded files). Software and many hardware peripherals can translate to and from encodings, and modern mainframes (such as IBM zSeries) include processor instructions, at the hardware level, to accelerate translation between character sets.

There is an EBCDIC-oriented Unicode Transformation Format called UTF-EBCDIC proposed by the Unicode consortium, designed to allow easy updating of EBCDIC software to handle Unicode, but not intended to be used in open interchange environments. Even on systems with extensive EBCDIC support, it has not been popular. For example, z/OS supports Unicode (preferring UTF-16 specifically), but z/OS only has limited support for UTF-EBCDIC.

IBM AIX running on the RS/6000 and its descendants including the IBM Power Systems, Linux running on z Systems, and operating systems running on the IBM PC and its descendants use ASCII, as did AIX/370 and AIX/390 running on System/370 and System/390 mainframes.

Compatibility with ASCII

The fact that all the code points were different was less of a problem for inter-operating with ASCII than the fact that sorting EBCDIC put lowercase letters before uppercase letters and letters before numbers, exactly the opposite of ASCII.

Software portability and data exchange are hindered by EBCDIC's lack of codes for several symbols (such as the brace characters) commonly used in programming and in network communications.

The gaps between some letters made simple constructions that worked in ASCII fail on EBCDIC. For example, 'Z' minus 'A' was 40, not 25. This sometimes caused problems when porting software from ASCII systems.

All ASCII codes stored within an eight-bit byte had nonnegative values on systems such as the PDP-11 that treated bytes as signed quantities. Software on those platforms often took advantage of that property, causing problems when it was ported to EBCDIC-based environments where many character codes had a 1 as the "sign" bit.

By using all eight bits EBCDIC may have encouraged the use of the eight-bit byte by IBM, while ASCII was more likely to be adopted by systems with 36 bits (as five seven-bit ASCII characters fit into one word). As eight-bit bytes became widespread, ASCII systems sometimes used the "unused" bit for other purposes, thus making it more difficult to transition to larger character sets.

Codepage layout

Further information: EBCDIC code pages

The table below is based on CCSID 037, one of the code page variants of EBCDIC; it shows only the basic (English) EBCDIC characters. Characters 00–3F and FF are controls, 40 is space, 41 is no-break space (RSP: "Required Space"), E1 is numeric space (NSP: "Numeric Space"), and CA is soft hyphen. Characters are shown with their equivalent Unicode codes. Unassigned codes are typically filled with international or region-specific characters in the various EBCDIC code page variants, but the punctuation marks and other special characters, such as cent sign, are often moved around as well; only the letters and numbers and space have the same assignments in all EBCDIC code pages.

In each table cell below, the first row is an abbreviation for a control code or (for printable characters) the character itself; the second row is the Unicode code; and the third row is decimal value of the EBCDIC code.

EBCDIC
_0 _1 _2 _3 _4 _5 _6 _7 _8 _9 _A _B _C _D _E _F
 
0_
 		 NUL
0000
0		 SOH
0001
1		 STX
0002
2		 ETX
0003
3		 SEL

4		 HT
0009
5		 RNL

6		 DEL
007F
7		 GE

8		 SPS

9		 RPT

10		 VT
000B
11		 FF
000C
12		 CR
000D
13		 SO
000E
14		 SI
000F
15
 
1_
 		 DLE
0010
16		 DC1
0011
17		 DC2
0012
18		 DC3
0013
19		 RES ENP

20		 NL
0085
21		 BS
0008
22		 POC

23		 CAN
0018
24		 EM
0019
25		 UBS

26		 CU1

27		 IFS
001C
28		 IGS
001D
29		 IRS
001E
30		 IUS ITB
001F
31
 
2_
 		 DS

32		 SOS

33		 FS

34		 WUS

35		 BYP INP

36		 LF
000A
37		 ETB
0017
38		 ESC
001B
39		 SA

40		 SFE

41		 SM SW

42		 CSP

43		 MFA

44		 ENQ
0005
45		 ACK
0006
46		 BEL
0007
47
 
3_
 

48

49		 SYN
0016
50		 IR

51		 PP

52		 TRN

53		 NBS

54		 EOT
0004
55		 SBS

56		 IT

57		 RFF

58		 CU3

59		 DC4
0014
60		 NAK
0015
61

62		 SUB
001A
63
 
4_
 		 SP
0020
64		 RSP
00A0
65

66

67

68

69

70

71

72

73

74		 .
002E
75		 <
003C
76		 (
0028
77		 +
002B
78		 |
007C
79
 
5_
 		 &
0026
80

81

82

83

84

85

86

87

88

89		 !
0021
90		 $
0024
91		 *
002A
92		 )
0029
93		 ;
003B
94		 ¬
00AC
95
 
6_
 		 -
002D
96		 /
002F
97

98

99

100

101

102

103

104

105		 ¦
00A6
106		 ,
002C
107		 %
0025
108		 _
005F
109		 >
003E
110		 ?
003F
111
 
7_
 

112

113

114

115

116

117

118

119

120		 `
0060
121		 :
003A
122		 #
0023
123		 @
0040
124		 '
0027
125		 =
003D
126		 "
0022
127
 
8_
 

128		 a
0061
129		 b
0062
130		 c
0063
131		 d
0064
132		 e
0065
133		 f
0066
134		 g
0067
135		 h
0068
136		 i
0069
137

138

139

140

141

142		 ±
00B1
143
 
9_
 

144		 j
006A
145		 k
006B
146		 l
006C
147		 m
006D
148		 n
006E
149		 o
006F
150		 p
0070
151		 q
0071
152		 r
0072
153

154

155

156

157

158

159
 
A_
 

160		 ~
007E
161		 s
0073
162		 t
0074
163		 u
0075
164		 v
0076
165		 w
0077
166		 x
0078
167		 y
0079
168		 z
007A
169

170

171

172

173

174

175
 
B_
 		 ^
005E
176

177

178

179

180

181

182

183

184

185		 [
005B
186		 ]
005D
187

188

189

190

191
 
C_
 		 {
007B
192		 A
0041
193		 B
0042
194		 C
0043
195		 D
0044
196		 E
0045
197		 F
0046
198		 G
0047
199		 H
0048
200		 I
0049
201		 SHY
00AD
202

203

204

205

206

207
 
D_
 		 }
007D
208		 J
004A
209		 K
004B
210		 L
004C
211		 M
004D
212		 N
004E
213		 O
004F
214		 P
0050
215		 Q
0051
216		 R
0052
217

218

219

220

221

222

223
 
E_
 		 \
005C
224		 NSP
2007
225		 S
0053
226		 T
0054
227		 U
0055
228		 V
0056
229		 W
0057
230		 X
0058
231		 Y
0059
232		 Z
005A
233

234

235

236

237

238

239
 
F_
 		 0
0030
240		 1
0031
241		 2
0032
242		 3
0033
243		 4
0034
244		 5
0035
245		 6
0036
246		 7
0037
247		 8
0038
248		 9
0039
249

250

251

252

253

254		 EO

255
_0 _1 _2 _3 _4 _5 _6 _7 _8 _9 _A _B _C _D _E _F

Criticism and humor

Open-source software advocate and hacker Eric S. Raymond writes in his Jargon File that EBCDIC was almost universally loathed by early hackers and programmers. The Jargon File 4.4.7 gives the following definition:[6]

EBCDIC: /eb´s@·dik/, /eb´see`dik/, /eb´k@·dik/, n.

[abbreviation, Extended Binary Coded Decimal Interchange Code] An alleged character set used on IBM dinosaurs. It exists in at least six mutually incompatible versions, all featuring such delights as non-contiguous letter sequences and the absence of several ASCII punctuation characters fairly important for modern computer languages (exactly which characters are absent varies according to which version of EBCDIC you're looking at). IBM adapted EBCDIC from punched card code in the early 1960s and promulgated it as a customer-control tactic (see connector conspiracy), spurning the already established ASCII standard. Today, IBM claims to be an open-systems company, but IBM's own description of the EBCDIC variants and how to convert between them is still internally classified top-secret, burn-before-reading. Hackers blanch at the very name of EBCDIC and consider it a manifestation of purest evil.

— The Jargon file 4.4.7

EBCDIC design was also the source of many jokes. One such joke went:

Professor: "So the American government went to IBM to come up with an encryption standard, and they came up with—"
Student: "EBCDIC!"

References to the EBCDIC character set are made in the classic Infocom adventure game series Zork. In the "Machine Room" in Zork II, EBCDIC is used to imply an incomprehensible language:

This is a large room full of assorted heavy machinery, whirring noisily. The room smells of burned resistors. Along one wall are three buttons which are, respectively, round, triangular, and square. Naturally, above these buttons are instructions written in EBCDIC...

A similar description can be found in the "Maintenance Room" in Zork:

This is what appears to have been the maintenance room for Flood Control Dam #3, judging by the assortment of tool chests around the room. Apparently, this room has been ransacked recently, for most of the valuable equipment is gone. On the wall in front of you is a group of buttons, which are labelled in EBCDIC. However, they are of different colors: Blue, Yellow, Brown, and Red.

See also

References

  1. 1 2 Mackenzie, Charles E. (1980). Coded Character Sets, History and Development. The Systems Programming Series (1 ed.). Addison-Wesley Publishing Company, Inc. ISBN 0-201-14460-3. LCCN 77-90165. ISBN 978-0-201-14460-4. Retrieved 2016-05-22.
  2. ↑ Bemer, Bob. "EBCDIC and the P-Bit". Retrieved July 2, 2013.
  3. ↑ They had 4 staff on the final 21-member ASA X3.2 sub-committee
  4. ↑ "...but their printers and punches were not ready to handle ASCII, and IBM just HAD to announce.", EBCDIC and the P-Bit, Bob Bemer
  5. ↑ IBMnt (2008). "IBM confirms the use of EBCDIC in their mainframes as a default practice". Retrieved 2008-06-16.
  6. ↑ "EBCDIC". Jargon File.
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