View source for DEC RADIX 50

{{Short description|Character encoding}}
{{Use dmy dates|date=June 2020|cs1-dates=y}}
{{Use list-defined references|date=December 2021}}
'''RADIX&nbsp;50'''<ref name="DEC_1965_PDP-6"/><ref name="DEC_1968_PDP-9"/><ref name="DEC_1971_PAL-11R"/> or '''RAD50'''<ref name="DEC_1971_PAL-11R"/> (also referred to as '''RADIX50''',<ref name="Durda_2004"/> '''RADIX-50'''<ref name="Compaq_1999_Fortran-77"/> or '''RAD-50'''), is an uppercase-only [[character encoding]] created by [[Digital Equipment Corporation]] (DEC) for use on their [[DECSYSTEM-20|DECsystem]], [[Programmed Data Processor|PDP]], and [[VAX]] computers.

RADIX&nbsp;50's 40-character repertoire (050 in [[octal]]) can encode six characters plus four additional bits into one [[36-bit computing|36-bit]] machine [[word (computer architecture)|word]] ([[PDP-6]], [[PDP-10]]/DECsystem-10, [[DECSYSTEM-20]]), three characters plus two additional bits into one [[18-bit computing|18-bit]] word ([[PDP-9]],<ref name="DEC_1968_PDP-9"/> [[PDP-15]]),<ref name="Jones_2018"/> or three characters into one [[16-bit computing|16-bit]] word ([[PDP-11]], VAX).<ref name="DEC_1971_PAL-11R"/>

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

==36-bit systems==
In 36-bit DEC systems RADIX&nbsp;50 was commonly used in [[symbol table]]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#Identifier name character encoding|SQUOZE character encoding scheme]] used in [[IBM]]'s [[SHARE Operating System]] for representing object code symbols, DEC's variant was also sometimes called '''DEC Squoze''',<ref name="Murrell_2005"/> however, IBM SQUOZE packed six characters of a 50-character alphabet plus two additional flag bits into one 36-bit word.<ref name="Jones_2018"/>

RADIX&nbsp;50 was not normally used in 36-bit systems for encoding ordinary character strings; file names were normally encoded as six [[six-bit character code|six-bit]] characters, and full ASCII strings as five seven-bit characters and one unused bit per 36-bit word.

{| class="wikitable"
|+ '''PDP-6,<ref name="DEC_1965_PDP-6"/> PDP-10/DECsystem-10, DECSYSTEM-20'''<ref name="Durda_2004"/>
!style="background:#ccffff" rowspan=2|Most<br>significant<br>bits
!colspan="8"|Least significant bits
|-
!width="10%"|000
!width="10%"|001
!width="10%"|010
!width="10%"|011
!width="10%"|100
!width="10%"|101
!width="10%"|110
!width="10%"|111
|-
!style="background:#ccffff"| 000
|style="background:white"| space ||style="background:#eeeeff"| 0 ||style="background:#eeeeff"| 1 ||style="background:#eeeeff"| 2 ||style="background:#eeeeff"| 3 ||style="background:#eeeeff"| 4 ||style="background:#eeeeff"| 5 ||style="background:#eeeeff"| 6
|-
!style="background:#ccffff"| 001
|style="background:#eeeeff"| 7 ||style="background:#eeeeff"| 8 ||style="background:#eeeeff"| 9 ||style="background:#eeffee"| A ||style="background:#eeffee"| B ||style="background:#eeffee"| C ||style="background:#eeffee"| D ||style="background:#eeffee"| E
|-
!style="background:#ccffff"| 010
|style="background:#eeffee"| F ||style="background:#eeffee"| G ||style="background:#eeffee"| H ||style="background:#eeffee"| I ||style="background:#eeffee"| J ||style="background:#eeffee"| K ||style="background:#eeffee"| L ||style="background:#eeffee"| M
|-
!style="background:#ccffff"| 011
|style="background:#eeffee"| N ||style="background:#eeffee"| O ||style="background:#eeffee"| P ||style="background:#eeffee"| Q ||style="background:#eeffee"| R ||style="background:#eeffee"| S ||style="background:#eeffee"| T ||style="background:#eeffee"| U
|-
!style="background:#ccffff"| 100
|style="background:#eeffee"| V ||style="background:#eeffee"| W ||style="background:#eeffee"| X ||style="background:#eeffee"| Y ||style="background:#eeffee"| Z ||style="background:#ffeeee"| . ||style="background:#ffeeee"| $ ||style="background:#ffeeee"| %
|}

==18-bit systems==
RADIX&nbsp;50 (also called '''Radix 50<sub>8</sub>''' format<ref name="DEC_1968_PDP-9"/>) 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").<ref name="DEC_1968_PDP-9"/>

=={{anchor|MOD40}}16-bit systems==
Some strings in DEC's 16-bit systems were encoded as 8-bit bytes, while others used RADIX&nbsp;50 (then also called '''MOD40''').<ref name="DEC_1971_PAL-11R"/><ref name="DEC_1971_PDP11"/><!-- what used 8-bit and what used squoze? -->

In RADIX&nbsp;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<sup>2</sup>&nbsp;+&nbsp;2×40<sup>1</sup>&nbsp;+&nbsp;3×40<sup>0</sup> = {{val|1683}}, followed by a second word containing the value 4×40<sup>2</sup>&nbsp;+&nbsp;5×40<sup>1</sup>&nbsp;+&nbsp;6×40<sup>0</sup> = {{val|6606}}. Thus, 16-bit words encoded values ranging from 0 (three spaces) to {{val|63999}} ("999"). When there were fewer than three characters in a word, the last word for the string was padded with trailing spaces.<ref name="DEC_1971_PAL-11R"/>

There were several minor variations of this encoding with differing interpretations of the 27, 28, 29 code points. Where RADIX&nbsp;50 was used for filenames stored on media, the code points represent the {{code|$}}, {{code|%}}, {{code|*}} characters, and will be shown as such when listing the directory with utilities such as DIR.<ref name="RT11_Radix50_Demo"/> When encoding strings in the PDP-11 assembler and other PDP-11 [[programming language]]s the code points represent the {{code|$}}, {{code|.}}, {{code|%}} characters, and are encoded as such with the default RAD50 macro in the global macros file, and this encoding was used in the [[symbol table]]s. Some early documentation for the [[RT-11]] operating system considered the code point 29 to be undefined.<ref name="DEC_1971_PAL-11R"/>

The use of RADIX&nbsp;50 was the source of the filename size conventions used by [[Digital Equipment Corporation]] PDP-11 operating systems. Using RADIX&nbsp;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. Similarly, a three-character device name such as "DL1" could also be stored in a 16-bit word. The period that separated the filename and its extension, and the colon separating a device name from a filename, was implied (i.e., was not stored and always assumed to be present).

{| class="wikitable"
|+ '''PDP-11, VAX'''<ref name="DEC_1971_PAL-11R"/><ref name="Compaq_1999_Fortran-77"/>
!style="background:#ccffff" rowspan=2|Most<br>significant<br>bits
!colspan="8"|Least significant bits
|-
!width="10%"|000
!width="10%"|001
!width="10%"|010
!width="10%"|011
!width="10%"|100
!width="10%"|101
!width="10%"|110
!width="10%"|111
|-
!style="background:#ccffff"| 000
|style="background:white"| space ||style="background:#eeffee"| A ||style="background:#eeffee"| B ||style="background:#eeffee"| C ||style="background:#eeffee"| D ||style="background:#eeffee"| E ||style="background:#eeffee"| F ||style="background:#eeffee"| G
|-
!style="background:#ccffff"| 001
|style="background:#eeffee"| H ||style="background:#eeffee"| I ||style="background:#eeffee"| J ||style="background:#eeffee"| K ||style="background:#eeffee"| L ||style="background:#eeffee"| M ||style="background:#eeffee"| N ||style="background:#eeffee"| O
|-
!style="background:#ccffff"| 010
|style="background:#eeffee"| P ||style="background:#eeffee"| Q ||style="background:#eeffee"| R ||style="background:#eeffee"| S ||style="background:#eeffee"| T ||style="background:#eeffee"| U ||style="background:#eeffee"| V ||style="background:#eeffee"| W
|-
!style="background:#ccffff"| 011
|style="background:#eeffee"| X ||style="background:#eeffee"| Y ||style="background:#eeffee"| Z ||style="background:#ffeeee"| $ ||style="background:#ffeeee"| % . ||style="background:#ffeeee"| * % ||style="background:#eeeeff"| 0 ||style="background:#eeeeff"| 1
|-
!style="background:#ccffff"| 100
|style="background:#eeeeff"| 2 ||style="background:#eeeeff"| 3 ||style="background:#eeeeff"| 4 ||style="background:#eeeeff"| 5 ||style="background:#eeeeff"| 6 ||style="background:#eeeeff"| 7 ||style="background:#eeeeff"| 8 ||style="background:#eeeeff"| 9
|}

==See also==
* [[Base 40]]
* [[Base conversion]]
* [[Chen–Ho encoding]]
* [[Densely packed decimal]] (DPD)
* [[Hertz encoding]]
* [[Packed BCD]]
* [[Six-bit character code]]
* [[Split octal]]

==References==
{{reflist|refs=
<ref name="Murrell_2005">{{cite web |title=DEC/PDP Character Codes |at=DEC Squoze Character Table |author-first=Stephen J. |author-last=Murrell |date=2005 |website=rabbit.eng.miami.edu |publisher=[[University of Miami]] |url=http://rabbit.eng.miami.edu/info/decchars.html |access-date=2020-06-19 |url-status=live |archive-url=https://web.archive.org/web/20200619074801/http://rabbit.eng.miami.edu/info/decchars.html |archive-date=2020-06-19}}</ref>
<ref name="Durda_2004">{{cite web |author-first=Frank |author-last=Durda IV. |title=RADIX50 Character Code Reference |date=2004 |url=http://nemesis.lonestar.org/reference/telecom/codes/radix50.html |access-date=2005-03-31 |url-status=dead |archive-url=https://web.archive.org/web/20050331062525/http://nemesis.lonestar.org/reference/telecom/codes/radix50.html |archive-date=2005-03-31}}</ref>
<ref name="DEC_1965_PDP-6">{{cite book |title=PDP-6 Multiprogramming System Manual |chapter=Chapter VI: The Loader - The Radix 50 Representation of Symbols |id=DEC-6-0-EX-SYS-UM-IP-PRE00 |publisher=[[Digital Equipment Corporation]] (DEC) |publication-place=Maynard, Massachusetts, USA |date=1965 |page=57 |url=http://bitsavers.trailing-edge.com/pdf/dec/pdp6/DEC-6-0-EX-SYS-UM-IP-PRE00_Multiprogramming_System_Manual_1965.pdf |access-date=2014-07-10 |url-status=live |archive-url=https://web.archive.org/web/20140714140253/http://bitsavers.trailing-edge.com/pdf/dec/pdp6/DEC-6-0-EX-SYS-UM-IP-PRE00_Multiprogramming_System_Manual_1965.pdf |archive-date=2014-07-14}} (1+84+10 pages)</ref>
<ref name="DEC_1968_PDP-9">{{cite book |publisher=[[Digital Equipment Corporation]] |title=PDP-9 Utility Programs--Advanced Software System--Programmer's Reference Manual |date=1968 |chapter=Appendix 1 
|id=Order No. DEC-9A-GUAB-D |publication-place=Maynard, Massachusetts, USA |url=http://www.bitsavers.org/pdf/dec/pdp9/DEC-9A-GUAB-D_UTILITIES.pdf |access-date=2020-06-04 |url-status=live |archive-url=https://web.archive.org/web/20200604125926/http://www.bitsavers.org/pdf/dec/pdp9/DEC-9A-GUAB-D_UTILITIES.pdf |archive-date=2020-06-04}}</ref>
<ref name="Compaq_1999_Fortran-77">{{cite book |publisher=[[Compaq Computer Corporation]] |title=Compaq Fortran 77 Language Reference Manual |chapter=Appendix B.3: Radix-50 Constants and Character Set |date=1999 |url=http://www.helsinki.fi/atk/unix/dec_manuals/cf77au/olrm0398.htm |access-date=2012-10-14 |url-status=dead |archive-url=https://web.archive.org/web/20121014144235/http://www.helsinki.fi/atk/unix/dec_manuals/cf77au/olrm0398.htm |archive-date=2012-10-14}}</ref>
<ref name="Jones_2018">{{cite web |work=Operating Systems, Spring 2018 |title=Lecture 7, Object Codes, Loaders and Linkers - Final steps on the road to machine code |author-first=Douglas W. |author-last=Jones |author-link=Douglas W. Jones |date=2018 |publisher=Department of Computer Science, [[The University of Iowa]] |series=Part of the CS:3620 Operating Systems Collection |url=http://homepage.divms.uiowa.edu/~jones/opsys/notes/07.shtml |access-date=2020-06-06 |url-status=live |archive-url=https://web.archive.org/web/20200606164231/http://homepage.divms.uiowa.edu/~jones/opsys/notes/07.shtml |archive-date=2020-06-06}}</ref>
<ref name="DEC_1971_PAL-11R">{{cite book |title=PAL-11R Assembler - Programmer's Manual - Program Assembly Language and Relocatable Assembler for the Disk Operating System |date=May 1971 |orig-date=February 1971 |edition=2nd revised printing |chapter=8.10 .RAD50 |id=DEC-11-ASDB-D |publisher=[[Digital Equipment Corporation]] |publication-place=Maynard, Massachusetts, USA |page=8-8 |url=https://archive.org/details/bitsavers_decpdp11do11RAssemblerProgrammersManualMay71_2572677 |access-date=2020-06-18 |quote-page=8-8 |quote=[…] [[PDP-11]] systems programs often handle symbols in a specially coded form called RADIX 50 (this form is sometimes referred to as MOD40). This form allows 3 characters to be packed into 16 bits; therefore, any 6-character symbol can be held in two words. The single operand is of the form /CCC/ where the slash (the delimiter) can be any printable character except for = and : . The delimiters enclose the characters to be converted which may be A through Z, 0 through 9, dollar ($), dot (.) and space ( ). If there are fewer than 3 characters they are considered to be left justified and trailing spaces are assumed. […] The packing algorithm is as follows: […] A. Each character is translated into its RADIX 50 equivalent as indicated in the following table: Character - RADIX 50 Equivalent (octal): (space) - 0, A–Z - 1–32, $ - 33, . - 34, 0–9 - 36–47. Note that another character could be defined for code 35. […] B. The RADIX 50 equivalents for characters 1 through 3 (C1,C2,C3) are combined as follows: RESULT=((C1*50)+C2)*50+C3 […]}} [https://archive.org/details/bitsavers_decpdp11do11RAssemblerProgrammersManualMay71_2572677]</ref>
<ref name="DEC_1971_PDP11">{{cite book |title=PDP-11 Getting DOS on the Air |date=August 1971 |edition=1 |id=DEC-11-SYDC-D |publisher=[[Digital Equipment Corporation]] |publication-place=Maynard, Massachusetts, USA |url=https://archive.org/details/bitsavers_decpdp11dotingDOSontheAirAug71_3085688 |access-date=2020-06-18}} [https://archive.org/download/bitsavers_decpdp11dotingDOSontheAirAug71_3085688/DEC-11-SYDC-D_Getting_DOS_on_the_Air_Aug71.pdf]</ref>
<ref name="RT11_Radix50_Demo">{{cite web |title=RT11 Radix50 Demo |url=https://commons.wikimedia.org/wiki/File:RT11_Radix50_Demo.gif}}</ref>
}}

==Further reading==
* {{cite web |title=Squoze your data |author-first=Al |author-last=Williams <!-- |author-link=Al Williams (author)??? --> |date=2016-11-22 |work=Hackaday |url=https://hackaday.com/2016/11/22/squoze-your-data/ |access-date=2020-06-06 |url-status=live |archive-url=https://web.archive.org/web/20200606101541/https://hackaday.com/2016/11/22/squoze-your-data/ |archive-date=2020-06-06}}

==External links==
* https://github.com/turbo/ptt-its/blob/master/doc/info/midas.25

{{Digital Equipment Corporation}}
{{character encoding}}

{{DEFAULTSORT:Radix-50}}
[[Category:Character encoding]]
[[Category:Character sets]]
[[Category:Digital Equipment Corporation]]