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 Electric in conjunction with their KDF9 machine in the mid-1960s.

Although the word ' byte' had been coined by the designers of the IBM 7030 Stretch for a group of eight bits, it was not yet well known, and English Electric used the word 'syllable' for what is now called a byte.

Machine code programming used an unusual form of octal, known locally as 'bastardized octal'. It represented 8 bits with three octal digits but the first digit represented only the two most-significant bits, whilst the others the remaining two groups of three bits each. A more polite colloquial name was 'silly octal', derived from the official name which was ''syllabic octal'' (also known as 'slob-octal' or 'slob' notation,).

This 8-bit notation was similar to the later 16-bit split octal notation.

Split octal

''Split octal'' is an unusual address notation used by Heathkit's PAM8 and portions of HDOS for the Heathkit H8 in the late 1970s (and sometimes up to the present). It was also used by Digital Equipment Corporation (DEC).

Following this convention, 16-bit numbers were split into two 8-bit numbers printed separately in octal, that is base 8 on 8-bit boundaries: the first location was "000.000" and the location after "000.377" was "001.000".

In order to distinguish numbers in split-octal notation from ordinary 16-bit octal numbers, the two digit groups were often separated by a slash (/), dot (.), colon (:) hyphen (-), or hash mark (#).

Most mini- and micro-computers used either straight octal (377 was followed by 400) or hexadecimal. With the introduction of the optional HA8-6 Z80 processor replacement for the 8080 board, the front-panel keyboard got a new set of labels and hexadecimal notation was used instead of octal.

Through tricky number alignment the HP-16C and other Hewlett-Packard RPN calculators supporting base conversion can implicitly support numbers in split octal as well.

See also

* IBM SQUOZE
* DEC RADIX 50
* Squawk code
* Segment:offset addressing

References

{{reflist, refs=
{{anchor, Beard-1997{{cite magazine , title=The KDF9 Computer — 30 Years On , author-first=Bob , author-last=Beard , magazine= Resurrection - The Bulletin of the Computer Conservation Society , issn=0958-7403 , publisher= Computer Conservation Society (CCS) , volume= , number=18 , date=Autumn 1997 , orig-date=1996-10-01 , pages=7–15 , 11, url=http://www.cs.man.ac.uk/CCS/Archive/Resurrection/pdf/res18.pdf , access-date=2020-07-27 , url-status=live , archive-url=https://web.archive.org/web/20200727140754/http://www.cs.man.ac.uk/CCS/Archive/Resurrection/pdf/res18.pdf , archive-date=2020-07-27}

(NB. This is an edited version of a talk given to North West Group of the Society at the Museum of Science and Industry, Manchester, UK on 1996-10-01. It mentions the term "slob" and "slob-octal" as equivalent to "syllabic octal".)
{{cite web , title=Architecture of the English Electric KDF9 computer. , version=Version 1 , date=September 2009 , publisher= Computer Conservation Society (CCS) , id=CCS-N4X2 , url=http://www.ourcomputerheritage.org/ccs-n2x2.pdf , access-date=2020-07-27 , url-status=live , archive-url=https://web.archive.org/web/20200404195007/http://www.ourcomputerheritage.org/ccs-n2x2.pdf , archive-date=2020-07-27 (NB. Refers to Beard's 1997 #Beard-1997, article.)
{{cite book , title=Director - Manual , type=Flowchart , publisher=English Electric , date=c. 1960s , work=KDF 8 , pages=40–49 , url=http://sw.ccs.bcs.org/KDF9/directorManuals/20090803114911646.pdf , access-date=2020-07-27 , url-status=live , archive-url=https://web.archive.org/web/20200727222921/http://sw.ccs.bcs.org/KDF9/directorManuals/20090803114911646.pdf , archive-date=2020-07-27 (10 pages) (NB. Mentions the term "syllabic octal".)
{{cite web , title=As I recall some DEC utilities supported 'split octal' which was base 8 on 8 bit boundaries , author-first=Chuck , author-last=McManis , date=2016-12-09 , work=Hacker News: Combinator , url=https://news.ycombinator.com/item?id=13140527 , access-date=2022-07-17 , url-status=live , archive-url=https://web.archive.org/web/20200727003857/https://news.ycombinator.com/item?id=13140527 , archive-date=2020-07-27
{{cite book , title=Control Data 8092 TeleProgrammer: Programming Reference Manual , date=1964 , id=IDP 107a , publisher=Control Data Corporation , location=Minneapolis, Minnesota, USA , url=http://bitsavers.org/pdf/cdc/809x/IDP107a_8092pgmRef_1964.pdf , access-date=2020-07-27 , url-status=live , archive-url=https://web.archive.org/web/20200525053524/http://bitsavers.org/pdf/cdc/809x/IDP107a_8092pgmRef_1964.pdf , archive-date=2020-05-25
{{cite magazine , title=Control the World! (Or at Least a Few Analog Points) , author-first=Steve , author-last=Ciarcia , author-link=Steve Ciarcia , location=Glastonbury, Connecticut, USA , magazine= BYTE – the small systems journal , issn=0360-5280 , publisher=BYTE Publications Inc. , date=September 1977 , volume=2 , number=9 , pages=30, 32, 34, 36, 38–40, 42–43, 156–158, 160–161 57–158, url=https://vintageapple.org/byte/pdf/197709_Byte_Magazine_Vol_02-09_Music_and_Computers.pdf , access-date=2020-07-31 , url-status=live , archive-url=https://web.archive.org/web/20190720194118/https://vintageapple.org/byte/pdf/197709_Byte_Magazine_Vol_02-09_Music_and_Computers.pdf , archive-date=2019-07-20
{{cite magazine , title=Building the Heath H8 Computer , author-first=Paul R. , author-last=Poduska , location=Nashua, New Hampshire, USA , magazine= BYTE – the small systems journal , issn=0360-5280 , publisher=BYTE Publications Inc. , date=March 1979 , volume=4 , number=3 , pages=12–13, 124–130, 132–134, 136–138, 140 29, 138, url=https://worldradiohistory.com/Archive-Byte/70s/Byte-1979-03.pdf , access-date=2020-07-31 , url-status=live , archive-url=https://web.archive.org/web/20200708173537/https://worldradiohistory.com/Archive-Byte/70s/Byte-1979-03.pdf , archive-date=2019-07-08
{{cite book , title=The 8080/Z-80 Assembly Language: Techniques for Improved Programming , author-first=Alan R. , author-last=Miller , date=1981 , orig-date=June 1980 , edition=1 , location=New York, USA , publisher= John Wiley & Sons, Inc. , isbn=0-471-08124-8 , lccn=80-21492 , id=ark:/13960/t4zg8792b. {{ISBN, 978-0-471-08124-1 , url=https://archive.org/stream/8080_and_Z-80_Assembly_Language_Techniques_1981_John_Wiley_and_Sons/8080_and_Z-80_Assembly_Language_Techniques_1981_John_Wiley_and_Sons_djvu.txt , access-date=2022-07-17 (1+x+319+2 pages)
{{cite web , title=A8008 8008 (1975) cross-assembler A8008 8008 (1975) cross-assembler , date=2019-10-02 , author-first=Herbert "Herb" R. , author-last=Johnson , url=http://www.retrotechnology.com/restore/a8008.html , access-date=2020-07-31 , url-status=live , archive-url=https://web.archive.org/web/20200207034842/http://www.retrotechnology.com/restore/a8008.html , archive-date=2020-02-07
{{cite book , title=Introduction to number systems , chapter=39. Split-Octal Concept , author-first=Forest , author-last=Belt , publisher=Computer Diagnostics , date= , pages=48–50 , url=https://f01.justanswer.com/LVyCWET7/b0802.pdf , access-date=2020-07-31 , url-status=live , archive-url=https://web.archive.org/web/20200731211259/https://f01.justanswer.com/LVyCWET7/b0802.pdf , archive-date=2020-07-31 (iv+56 pages)
{{cite web , title={31} Binary, Decimal Octal, Split Octal, and HEX , author-first=Craig , author-last=Andrews , work=Bits Of The Golden Age , type=Educational video , date=2020 , url=https://www.youtube.com/watch?v=9v2OiicrzrQ , access-date=2022-07-17
{{cite web , title=H-8 Technical details , author-first=Dave , author-last=Wallace , date=2011-07-23 , orig-date=2001-09-29, 2000 , url=http://davidwallace2000.home.comcast.net/~davidwallace2000/h8/technical.htm#z80%20cpu , url-status=dead , archive-url=https://web.archive.org/web/20110723052102/http://davidwallace2000.home.comcast.net/~davidwallace2000/h8/technical.htm#z80%20cpu , archive-date=2011-07-23
{{cite web , title=hp16 and split octal conversion , date=2021-12-02 , orig-date=2021-12-01 , author1=Roland57 , author-first2=Jean François , author-last2=Garnier , work=The Museum of HP Calculators (MoHPC) , url=https://www.hpmuseum.org/forum/thread-17777-post-154980.html , access-date=2022-07-17 , url-status=live , archive-url=https://web.archive.org/web/20220717073142/https://www.hpmuseum.org/forum/thread-17777-post-154980.html , archive-date=2022-07-17 , quote= ��Before you write a program on the hp16 to do the conversion, just put a zero between the two bytes, e.g. A9oC2 hex. Conversion to octal gives 251o302, the split octal value (with "o" als the digit zero to separate the two bytes). Same works for octal to hex. 377o377 octal to hex gives FFoFF ��Also usable on other machines with base conversion such as the 32S/ SII, the 42S or the 41C with Advantage ROM. It works because 3 hex digits are 12 bits, exactly 4 oct digits. ��}

Early microcomputers
Binary arithmetic
Positional numeral systems