EBCDIC

Extended Binary Coded Decimal Interchange Code^[1] (EBCDIC;^[1] /ˈɛbsɪdɪk/) is an eight-bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems. It 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 supported by various non-IBM platforms, such as Fujitsu-Siemens' BS2000/OSD, OS-IV, MSP, and MSP-EX, the SDS Sigma series, Unisys VS/9, Burroughs MCP and ICL VME.

History

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

EBCDIC 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 seven-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 six bits. The distinct encoding of 's' and 'S' (using position 2 instead of 1) was maintained from punched cards where it was desirable not to have hole punches too close to each other to ensure the integrity of the physical card.

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.^[2] 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^[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 letters made simple code that worked in ASCII fail on EBCDIC. For example, "for (c='A';c<='Z';++c)" would set c to the 26 letters in the ASCII alphabet, but 41 characters including a number of unassigned ones in EBCDIC. Fixing this required complicating the code with function calls which was greatly resisted by programmers.

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 such as parity, thus making it more difficult to transition to larger character sets.

Code page layout

The table below shows the "invariant subset" of EBCDIC, which are characters that should have the same assignments on all EBCDIC code pages. It also shows (in boxes) missing ASCII and EBCDIC punctuation, located where then are in CCSID 037 (one of the code page variants of EBCDIC). Unassigned codes are typically filled with international or region-specific characters in the various EBCDIC code page variants, but the characters in boxes are often moved around as well.

In each table cell below, the first row is an abbreviation for a control code or (for printable characters) the character itself; and the second row is the Unicode code (blank for controls that don't exist in Unicode).

Definitions of non-unicode EBCDIC controls

^[5]

Criticism and humor

Open-source software advocate and software developer Eric S. Raymond writes in his Jargon File that EBCDIC was loathed by hackers, by which he meant^[6] members of a subculture of enthusiastic programmers. The Jargon File 4.4.7 gives the following definition:^[7]

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...

See also

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

References

External links

• Character Data Representation Architecture (CDRA) from IBM Contains IBM's official information on code pages and character sets.
  • Code page 37
  • Code page 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
• EBCDIC-code pages with Latin-1-charset (JavaScript)
• All EBCDIC code pages and 3270 graphics escape codes at the Wayback Machine (archived August 27, 2016)