🚀 go-pugleaf

In article <22...@charon.cwi.nl> d...@cwi.nl (Dik T. Winter) writes:
*
*  > In article <1990Oct03.172748.18683@virtech.uucp> jje@virtech.uucp (Jeremy J. Epstein) writes:
*  > >What were the advantages/disadvantages of 7 track as opposed to
*  > >9 track?
*  > Hmmm... Obviously you can not write whole bytes to 7 track tape (yes,
*  > actually you can - after a clever hack :-).
*
* Oh, but in the days of 7 track tape you could write a byte plus parity.
* It is only with the introduction of the 360 that IBM proclaimed that from
* that time onward a byte would be 8 bits.  And for some reason everybody
* followed.  (Yes, also IBM has known 6 bit bytes!)
*
Welll...
--
7-track was designed to accommodate the 6-bit "BCD" or "Field
Code" character/byte, plus a parity bit.  It really had nothing to do with
the number of heads which could be spread across the tape.
--
9-track was designed to accommodate the 8-bit "EBCDIC" character/byte, plus
a parity bit.
--
"Data Translation" applied to 7-track tapes on systems with 8-bit bytes:
it simply swapped 6-bit vs. 8-bit character codes.  Of course, it limited
the 8-bit code to only the 64 EBCDIC characters corresponding to the
original BCD character set.  I disremember what it did when told to
do 8-to-6 for an EBCDIC code outside the nominal map.
--
"Data Conversion" took three 8-bit codes (24 bits) from the system and did
them as four 6-bit codes on tape.
--
Yes, it was/is possible (at least on IBM drives of the era) to turn on
both Translation and Conversion, but I can't recall which was done first
or what the real result was.  I do remember that most folk regarded the
combination as spectacularly unuseful.
-------------
regardz,
Ken