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Syllabic octal and split octal are two similar notations for 8-bit and 16-bit , respectively, used in some historical contexts.
Although the word 'byte' had been coined by the designers of the IBM 7030 Stretch for a group of eight , 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 (with values 0..3), whilst the others the remaining two groups of three bits (with values 0..7) 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.
Following this convention, 16-bit addresses were split into two 8-bit numbers printed separately in octal, that is base 8 on 8-bit boundaries: the first memory location was "000.000" and the memory location after "000.377" was "001.000" (rather than "000.400").
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 (:), comma (,), hyphen (-), or hash mark (#).
Most and used either straight octal (where 377 is 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.
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