On Thu, 17 May 2001 15:39:02 -0500, Peter Constable wrote:
> Can anyone clarify for me how big a byte has ever been? (If you could
> identify the particular hardware, that would be helpful.)
The TR440, a German brand of computer (designed and built here
at Konstanz), in use circa 1975..1990 (I don't remember the exact
living-span), had a 48 + 2 bit word: 2 bits of data-type flag,
48 bits of data proper. The adressing was mostly per 24-bit
half-words, as a machine instruction, or a pointer, were stored
in a halfword each (with the data-type flag set to 2).
For character-type processing (data-type flag = 3), there were two
particular machine instructions, termed BNZ and CNZ ("bringe/speichere
nächstes Zeichen" = load/store next character) which could address
6-bit, 8-bit, or 12-bit bytes, at the programmers discretion (I do
not quite remember whether these instructions could also handle
smaller or larger fractions of a machine-word, such as 2-bit, 4-bit,
or 24-bit chunks; in any case, there were all 48 dat bits used per
word).
However, most available software only exploited the 8-bit variant,
and the only character encoding defined by the input/output routines
of the operating system was an 8-bit single-byte coded character set
(not counting a 6-bit byte mode available for backwards compatibility
with the predecessor TR4). There was even another machine instruction,
TOK ("transportiere Oktaden" = move octets) which was particularly
designed for the COBOL compiler and (as its name implies) could only
handle 8-bit bytes.
Note that the term "Oktade" (octet) was used by the vendor of this
machine as early as 1975 (or was it 1972?).
Aside: as a result of an "integrierte Hardware-Software-Entwicklung"
(integrated hardware-software development), this TOK instruction used
a particular addressing scheme, viz. a sequential numbering of the
octets. Hence, the COBOL compiler multiplied the usual address (used
elsewhere, e. g. in storage management) by 3 to arrive at an octet
address, and then the hardware divided that address by 3 to arrive
at a storage-address used elsewhere (e. g. in the micro-program for
storage access). Weird...
Best wishes,
Otto Stolz
