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EBCDIC
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EBCDIC

EBCDIC (Fully, "Extended Binary Coded Decimal Interchange Code") is an 8 bit character encoding used on IBM mainframes and AS/400s. It is descended from punched cards and the corresponding six bit Binary Coded Decimal Code that most of IBM's computer peripherals of the late 1950s and early 1960s used. Outside of such IBM systems and compatible systems from other companies, ASCII (and its descendants such as Unicode) are normally used instead; EBCDIC is generally considered an anachronism.

Single byte EBCDIC takes up eight bits, which are divided in two pieces. The first four bits are called the zone and represent the category of the character, whereas the last four bits are the called the digit and identify the specific character. There are a number of different versions of EBCDIC, customised for different countries.

Some East Asian countries use a double byte extension of EBCDIC to allow display of Chinese, Japanese and Korean scripts for their mainframes. In the double byte extentension of EBCDIC, there are shift codes [0x0E,0x0F] to shift between the single byte and double byte modes.

IBM typically names all of its codepages with a number called a CCSID (Coded Character Set IDentifier). It is important to note that the same CCSID can have different character positions in a codepage. For example, the newline character can be a different byte value in os/390 open edition versus the other EBCDIC based operating systems. This becomes an issue when transferring EBCDIC based text data between machines.

History

EBCDIC was devised in 1963-1964 timeframe by IBM and announced with the release of the IBM System/360 line of mainframe computers at the apex of IBM’s mainframe monopoly. EBCDIC was the predecessor to ASCII, which was devised in 1968. EBCDIC is an 8 bit encoding, vs. the 7 bit encoding of ASCII. Many extensions to ASCII have been devised before Unicode became a standard.

There is a nice correspondence between hexadecimal character codes and punch card codes for EBCDIC — an important feature at the time. Unfortunately the Roman alphabet characters are numerically non-contiguous, which is a great annoyance for many of the more modern programming languages. It is more difficult to sort or select a range of characters in EBCDIC compared to ASCII (for example, sorting the range of characters [a-z] when accented characters are involved).

All IBM mainframe peripheralss and operating systems used EBCDIC. Their only lip service to ASCII was to provide an ASCII mode for reading magnetic tapes. Some mainframe applications can support Unicode, but it is not nearly as good as it could be.

There is an EBCDIC Unicode Transformation Format proposed by the Unicode consortium, but it is not intended to be used in open interchange environments.

Codepage layout

This is CCSID 500, a variant of EBCDIC. Characters 0x00–0x3F and 0xFF are controls, 0x40 is space, 0x41 is no-break space, 0xCA is soft hyphen.

    0 1 2 3 4 5 6 7 8 9 A B C D E F
40     â ä à á ã å ç ñ [ . < ( + !
50   & é ê ë è í î ï ì ß ] $ * ) ; ^
60   - / Â Ä À Á Ã Å Ç Ñ ¦ , % _ > ?
70   ø É Ê Ë È Í Î Ï Ì ` : # @ ' = "
80   Ø a b c d e f g h i « » ð ý þ ±
90   ° j k l m n o p q r ª º æ ¸ Æ ¤
A0   µ ~ s t u v w x y z ¡ ¿ Ð Ý Þ ®
B0   ¢ £ ¥ · © § ¼ ½ ¾ ¬ | ¯ ¨ ´ ×
C0   { A B C D E F G H I ­ ô ö ò ó õ
D0   } J K L M N O P Q R ¹ û ü ù ú ÿ
E0   \ ÷ S T U V W X Y Z ² Ô Ö Ò Ó Õ
F0   0 1 2 3 4 5 6 7 8 9 ³ Û Ü Ù Ú  

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