DEC Radix-50

DEC Radix-50

RADIX-50, commonly called Rad-50 or RAD50, is a character encoding created by Digital Equipment Corporation for use on their DECsystem, PDP, and VAX computers. RADIX-50's 40-character repertoire (050 in octal) allows up to 3 characters to be encoded and packed into 16 bits (PDP-11, VAX) or 6 characters plus flag information into one 36-bit word (PDP-6, PDP-10/DECsystem-10, DECSYSTEM-20).

The actual encoding differed between the 36-bit and 16-bit systems.

PDP-6, PDP-10/DECsystem-10, DECSYSTEM-20[1]
Most
significant
bits
Least significant bits
000 001 010 011 100 101 110 111
000 space 0 1 2 3 4 5 6
001 7 8 9 A B C D E
010 F G H I J K L M
011 N O P Q R S T U
100 V W X Y Z . $  %
PDP-11, VAX[2]
Most
significant
bits
Least significant bits
000 001 010 011 100 101 110 111
000 space A B C D E F G
001 H I J K L M N O
010 P Q R S T U V W
011 X Y Z $ .  % 0 1
100 2 3 4 5 6 7 8 9

Strings are encoded in successive words as needed, and the first character within each word is in the most significant position. For example, using the PDP-11 encoding, the string "ABCDEF", with character values 1, 2, 3, 4, 5, and 6, would be encoded as a word containing the value (1*40 + 2) * 40 + 3 = 1683 followed by a word containing the value (4*40 + 5) * 40 + 6 = 6606. Thus, 16-bit encoded values range from 0 (three spaces) to 63999 ("999"). When there are fewer characters in a word than it can hold, the string is padded with trailing spaces.

There were several minor variations of the encoding families. For example, the RT-11 operating system considered the character corresponding to value 011101 to be undefined, and some utility programs used that value to represent * instead.

The use of Rad-50 was the source of the filename size conventions used by the PDP-11 operating systems. Using Rad-50 encoding, six characters of filename could be stored in two sixteen-bit words while three more characters of extension (filetype) could be stored in a third sixteen-bit word. The period that separated the filename and extension was implied (not stored and always assumed to be present). Rad-50 was also commonly used in the symbol tables of the various PDP-11 programming languages.

References

  1. ^ Frank Durda IV. "RADIX50 Character Code Reference". 2004. http://nemesis.lonestar.org/reference/telecom/codes/radix50.html
  2. ^ Compaq Computer Corporation. "Compaq Fortran 77 Language Reference Manual, Appendix B.3: Radix-50 Constants and Character Set". 1999. http://www.helsinki.fi/atk/unix/dec_manuals/cf77au/olrm0398.htm

Wikimedia Foundation. 2010.

Игры ⚽ Нужно решить контрольную?

Look at other dictionaries:

  • RADIX-50 — (prononcer radix five zero) est un codage de caractères créé par DEC pour les ordinateurs de la série PDP, le DECsystem 10 et le DECSYSTEM 20. Le répertoire RADIX 50 comporte 40 caractères. Le nom RADIX 50 signifie « base 40 » :… …   Wikipédia en Français

  • Radix-50 — est un codage de caractère crée par DEC pour les ordinateurs de la série PDP, le DECsystem 10 et le DECSYSTEM 20. Le répertoire RADIX 50 comporte 40 caractères. Le nom RADIX 50 signifie « base 40 » : radix désigne une base en… …   Wikipédia en Français

  • Radix economy — Various proposals have been made to quantify the relative costs between using different radices in representing numbers.DefinitionThe radix economy E ( b , N ) for any particular number N in a given base b is equal to the number of digits needed… …   Wikipedia

  • ANSI escape code — ANSI code redirects here. For other uses, see ANSI (disambiguation). ANSI escape sequences are characters embedded in the text used to control formatting, color, and other output options on video text terminals. Almost all terminal emulators… …   Wikipedia

  • C0 and C1 control codes — Most character encodings, in addition to representing printable characters, may also represent additional information about the text, such as the position of a cursor, an instruction to start a new line, or a message that the text has been… …   Wikipedia

  • Control character — In computing and telecommunication, a control character or non printing character is a code point (a number) in a character set, that does not in itself represent a written symbol. It is in band signaling in the context of character encoding. All …   Wikipedia

  • ISO/IEC 646 — This article is about a character encoding standard. For the ISO C header file, see iso646.h. ISO/IEC 646:1991, Information technology ISO 7 bit coded character set for information interchange, is an ISO standard that since its first edition in… …   Wikipedia

  • ISO/IEC 8859-11 — ISO/IEC 8859 11:2001, Information technology 8 bit single byte coded graphic character sets Part 11: Latin/Thai alphabet, is part of the ISO/IEC 8859 series of ASCII based standard character encodings, first edition published in 2001. It is… …   Wikipedia

  • Multinational Character Set — The Multinational Character Set (MCS) is a character encoding created by Digital Equipment Corporation for use in the popular VT220 terminal. It was an 8 bit extension of ASCII that added accented characters, currency symbols, and other character …   Wikipedia

  • Baudot code — The Baudot code, invented by Émile Baudot,[1] is a character set predating EBCDIC and ASCII. It was the predecessor to the International Telegraph Alphabet No 2 (ITA2), the teleprinter code in use until the advent of ASCII. Each character in the… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”