EBCDIC

Extended Binary Coded Decimal Interchange Code (EBCDIC) 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.^[1] It is also employed on various non-IBM platforms such as Fujitsu-Siemens' BS2000/OSD, OS-IV, MSP, and MSP-EX, and Unisys VS/9 and MCP.

History

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, in contrast to, and 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,^[2] 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.^[3] The System/360 became wildly successful, and 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^[4] (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

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:^[5]

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

• List of EBCDIC code pages with Latin-1 character set
• codepage 037 (English, Portuguese)
• codepage 285 (Ireland, United Kingdom)
• UTF-EBCDIC

References

1. Bemer, Bob. "EBCDIC and the P-Bit". Retrieved July 2, 2013.
2. They had 4 staff on the final 21-member ASA X3.2 sub-committee
3. "...but their printers and punches were not ready to handle ASCII, and IBM just HAD to announce.", EBCDIC and the P-Bit, Bob Bemer
4. IBMnt (2008). "IBM confirms the use of EBCDIC in their mainframes as a default practice". Retrieved 2008-06-16.
5. "EBCDIC". Jargon File.

External links

• Character Data Representation Architecture (CDRA) from IBM Contains IBM's official information on codepages and charsets.
  • Codepage 37
  • Codepage 1047
• F.0 Appendix F. Code Pages from AS/400 International Application Development V4R2
• ICU Converter Explorer Contains more information about EBCDIC derived from IBM's CDRA, including DBCS EBCDIC (Double Byte Character Set EBCDIC)
• ICU Charset Mapping Tables Contains computer readable Unicode mapping tables for EBCDIC and many other character sets
• EBCDIC character list, including decimal and hex values, symbolic name, and character/function
• iconv.com Online tool to convert from ASCII to/from EBCDIC
• EBCDIC-codepages with Latin-1-charset (JavaScript)
• EBCDIC and the P-Bit (The Biggest Computer Goof Ever)