The Full Wiki

More info on DEC Radix-50

DEC Radix-50: Wikis

Advertisements

Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.

Encyclopedia

From Wikipedia, the free encyclopedia

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 big-endian, with the first character in the most significant position. For example, using the PDP-11 encoding, the string "ABC", with character values 1, 2, and 3, would be encoded as (1*40 + 2) * 40 + 3 = 1683. When there are fewer than three characters, they are padded with trailing spaces. 16-bit encoded values range from 0 (three spaces) to 63999 ("999").

This encoding inherently "pads" strings that are not multiples of 3 characters 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 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
Advertisements

Advertisements






Got something to say? Make a comment.
Your name
Your email address
Message