RADIX-50
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.
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 table
s of the various PDP-11 programming language
s.
Character encoding
A character encoding system consists of a code that pairs each character from a given repertoire with something else, such as a sequence of natural numbers, octets or electrical pulses, in order to facilitate the transmission of data through telecommunication networks or storage of text in...
created by Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
for use on their DECsystem
DECSYSTEM-20
The DECSYSTEM-20 was a 36-bit Digital Equipment Corporation PDP-10 mainframe computer running the TOPS-20 operating system.PDP-10 computers running the TOPS-10 operating system were labeled DECsystem-10 as a way of differentiating them from the PDP-11...
, PDP
Programmed Data Processor
Programmed Data Processor was the name of a series of minicomputers made by Digital Equipment Corporation. The name 'PDP' intentionally avoided the use of the term 'computer' because, at the time of the first PDPs, computers had a reputation of being large, complicated, and expensive machines, and...
, and VAX
VAX
VAX was an instruction set architecture developed by Digital Equipment Corporation in the mid-1970s. A 32-bit complex instruction set computer ISA, it was designed to extend or replace DEC's various Programmed Data Processor ISAs...
computers. RADIX-50's 40-character repertoire (050 in octal
Octal
The octal numeral system, or oct for short, is the base-8 number system, and uses the digits 0 to 7. Numerals can be made from binary numerals by grouping consecutive binary digits into groups of three...
) allows up to 3 characters to be encoded and packed into 16 bits (PDP-11
PDP-11
The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years...
, VAX) or 6 characters plus flag information into one 36-bit word (PDP-6
PDP-6
The PDP-6 was a computer model developed by Digital Equipment Corporation in 1963. It was influential primarily as the prototype for the later PDP-10; the instruction sets of the two machines are almost identical.The PDP-6 was DEC's first "big" machine...
, PDP-10
PDP-10
The PDP-10 was a mainframe computer family manufactured by Digital Equipment Corporation from the late 1960s on; the name stands for "Programmed Data Processor model 10". The first model was delivered in 1966...
/DECsystem-10, DECSYSTEM-20
DECSYSTEM-20
The DECSYSTEM-20 was a 36-bit Digital Equipment Corporation PDP-10 mainframe computer running the TOPS-20 operating system.PDP-10 computers running the TOPS-10 operating system were labeled DECsystem-10 as a way of differentiating them from the PDP-11...
).
The actual encoding differed between the 36-bit and 16-bit systems.
| 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 | . | $ | % |
| 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
RT-11
RT-11 was a small, single-user real-time operating system for the Digital Equipment Corporation PDP-11 family of 16-bit computers...
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 table
Symbol table
In computer science, a symbol table is a data structure used by a language translator such as a compiler or interpreter, where each identifier in a program's source code is associated with information relating to its declaration or appearance in the source, such as its type, scope level and...
s of the various PDP-11 programming language
Programming language
A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
s.