RADIX 50
or RAD50
(also referred to as RADIX50,
RADIX-50
or RAD-50), is an uppercase-only
character encoding
Character encoding is the process of assigning numbers to Graphics, graphical character (computing), characters, especially the written characters of Language, human language, allowing them to be Data storage, stored, Data communication, transmi ...
created by
Digital Equipment Corporation
Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president unt ...
(DEC) for use on their
DECsystem
DECsystem was a line of server computers from Digital Equipment Corporation. They were based on MIPS architecture processors and ran DEC's version of the UNIX operating system, called ULTRIX. They ranged in size from workstation-style desktop enc ...
,
PDP, and
VAX
VAX (an acronym for Virtual Address eXtension) is a series of computers featuring a 32-bit instruction set architecture (ISA) and virtual memory that was developed and sold by Digital Equipment Corporation (DEC) in the late 20th century. The V ...
computers.
RADIX 50's 40-character repertoire (050 in
octal
The octal numeral system, or oct for short, is the radix, base-8 number system, and uses the Numerical digit, digits 0 to 7. This is to say that 10octal represents eight and 100octal represents sixty-four. However, English, like most languages, ...
) can encode six characters plus four additional bits into one
36-bit
36-bit computers were popular in the early mainframe computer era from the 1950s through the early 1970s.
Starting in the 1960s, but especially the 1970s, the introduction of 7-bit ASCII and 8-bit EBCDIC led to the move to machines using 8-bit ...
machine
word
A word is a basic element of language that carries an semantics, objective or pragmatics, practical semantics, meaning, can be used on its own, and is uninterruptible. Despite the fact that language speakers often have an intuitive grasp of w ...
(
PDP-6
The PDP-6, short for Programmed Data Processor model 6, is a computer developed by Digital Equipment Corporation (DEC) during 1963 and first delivered in the summer of 1964.
It was an expansion of DEC's existing 18-bit systems to use a 36-bit da ...
,
PDP-10
Digital Equipment Corporation (DEC)'s PDP-10, later marketed as the DECsystem-10, is a mainframe computer family manufactured beginning in 1966 and discontinued in 1983. 1970s models and beyond were marketed under the DECsystem-10 name, especi ...
/DECsystem-10,
DECSYSTEM-20
The DECSYSTEM-20 was a 36-bit Digital Equipment Corporation PDP-10 mainframe computer running the TOPS-20 operating system (products introduced in 1977).
PDP-10 computers running the TOPS-10 operating system were labeled ''DECsystem-10'' as a ...
), three characters plus two additional bits into one
18-bit word (
PDP-9
The PDP-9, the fourth of the five 18-bit minicomputers produced by Digital Equipment Corporation, was introduced in 1966. A total of 445 PDP-9 systems were produced, of which 40 were the compact, low-cost PDP-9/L units..
History
The 18-bit PDP ...
,
PDP-15
The PDP-15 was the fifth and last of the 18-bit minicomputers produced by Digital Equipment Corporation. The PDP-1 was first delivered in December 1959 and the first PDP-15 was delivered in February 1970. More than 400 of these successors to th ...
),
or three characters into one
16-bit
16-bit microcomputers are microcomputers that use 16-bit microprocessors.
A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two mos ...
word (
PDP-11
The PDP-11 is a series of 16-bit minicomputers sold by Digital Equipment Corporation (DEC) from 1970 into the 1990s, one of a set of products in the Programmed Data Processor (PDP) series. In total, around 600,000 PDP-11s of all models were sold, ...
, VAX).
The actual encoding differs between the 36-bit and 16-bit systems.
36-bit systems
In 36-bit DEC systems RADIX 50 was commonly used in
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 (or symbols), constants, procedures and functions in a program's source code is associated with info ...
s for assemblers or compilers which supported six-character symbol names from a 40-character alphabet. This left four bits to encode properties of the symbol.
For its similarities to the
SQUOZE
SQUOZE (abbreviated as SQZ) is a memory-efficient representation of a combined source and relocatable object program file with a symbol table on punched cards which was introduced in 1958 with the SCAT assembler on the SHARE Operating System ( ...
encoding scheme used in
IBM's
SHARE Operating System
The SHARE Operating System (SOS) is an operating system introduced in 1959 by the SHARE user group. It is an improvement on the General Motors GM-NAA I/O operating system, the first operating system for the IBM 704. The main objective was to im ...
for representing object code symbols, DEC's variant was also sometimes called DEC Squoze,
however, IBM SQUOZE packed six characters of a 50-character alphabet plus two additional flag bits into one 36-bit word.
RADIX 50 was not normally used in 36-bit systems for encoding ordinary character strings; file names were normally encoded as six
six-bit characters, and full ASCII strings as five seven-bit characters and one unused bit per 36-bit word.
18-bit systems
RADIX 50 (also called Radix 50
8 format
) was used in Digital's 18-bit PDP-9 and PDP-15 computers to store symbols in symbol tables, leaving two extra bits per 18-bit word ("symbol classification bits").
16-bit systems
Some strings in DEC's 16-bit systems were encoded as 8-bit bytes, while others used RADIX 50 (then also called MOD40).
In RADIX 50, strings were encoded in successive words as needed, with the first character within each word located 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 + 2×40
1 + 3×40
0 = , followed by a second word containing the value 4×40
2 + 5×40
1 + 6×40
0 = . Thus, 16-bit words encoded values ranging from 0 (three spaces) to ("999"). When there were fewer than three characters in a word, the last word for the string was padded with trailing spaces.
There were several minor variations of this encoding. For example, the
RT-11
RT-11 (Real-time 11) is a discontinued small, low-end, single-user real-time operating system for the full line of Digital Equipment Corporation PDP-11 16-bit computers. RT-11 was first implemented in 1970. It was widely used for real-time computin ...
operating system considered the character corresponding to value () to be undefined,
and some utility programs used that value to represent the character instead.
The use of RADIX 50 was the source of the filename size conventions used by
Digital Equipment Corporation
Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president unt ...
PDP-11 operating systems. Using RADIX 50 encoding, six characters of a filename could be stored in two 16-bit words, while three more extension (file type) characters could be stored in a third 16-bit word. The period that separated the filename and its extension was implied (i.e., was not stored and always assumed to be present). RADIX 50 was also commonly used in the
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 (or symbols), constants, procedures and functions in a program's source code is associated with info ...
s of the various PDP-11
programming language
A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language.
The description of a programming ...
s.
See also
*
Packed BCD
In computing and electronic systems, binary-coded decimal (BCD) is a class of binary encodings of decimal numbers where each digit is represented by a fixed number of bits, usually four or eight. Sometimes, special bit patterns are used for ...
*
Hertz encoding
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...
*
Chen–Ho encoding
Chen–Ho encoding is a memory-efficient alternate system of binary encoding for decimal digits.
The traditional system of binary encoding for decimal digits, known as binary-coded decimal (BCD), uses four bits to encode each digit, resulting in ...
*
Densely packed decimal
Densely packed decimal (DPD) is an efficient method for binary encoding decimal digits.
The traditional system of binary encoding for decimal digits, known as binary-coded decimal (BCD), uses four bits to encode each digit, resulting in signifi ...
(DPD)
*
Six-bit character code
A six-bit character code is a character encoding designed for use on computers with word lengths a multiple of 6. Six bits can only encode 64 distinct characters, so these codes generally include only the upper-case letters, the numerals, some punc ...
*
Base 40
There are many different numeral systems, that is, writing systems for expressing numbers.
By culture / time period
By type of notation
Numeral systems are classified here as to whether they use positional notation (also known as place-value ...
*
Base conversion
Positional notation (or place-value notation, or positional numeral system) usually denotes the extension to any base of the Hindu–Arabic numeral system (or decimal system). More generally, a positional system is a numeral system in which th ...
*
Split octal
Syllabic octal and split octal are two similar notations for 8-bit and 16-bit octal numbers, respectively, used in some historical contexts.
Syllabic octal
''Syllabic octal'' is an 8-bit octal number representation that was used by English Ele ...
References
Further reading
*
External links
* https://github.com/turbo/ptt-its/blob/master/doc/info/midas.25
{{DEFAULTSORT:Radix-50
Character encoding
Character sets
Digital Equipment Corporation