12 Jan
1999
12 Jan
'99
1:02 a.m.
> Nop - or better partly correct - it is true that
not every punch
> combination was legel (that would be 4096 possible) but at least
------------
> there was a legal combination for any possible
8-Bit combination.
> Otherways I would have been impossible to boot from a punch card
> reader !
Since when do all machines have 8-bit instructions,
and since when do all
machines represent one instruction as one column on a card, and since
when do all machines have binary instructions?
Did I say this ? I just mentioned that there is a legal (within
IBM style 12 row cards) method to code all opssible 256 combinations
for 8 bit bytes - starting from 12,0,9,8,1 for x'00' up to 12,11,
0,9,8,7 for x'FF'.
I see no way why such a thing is conected to an 8 bit instruction -
it's only the way to encode a byte on one columne, which gives
80 bytes on a card - enough for the first step of a boot loader
There is no requirement for 256 legal punchings in a
column AFAIK.
Just to enter raw binary data from punch cards, and of course
to boot a machine - my main experiance about that comes from
the /370 world, or more exactly from SIEMENS /370 compatible
systems. I still love the simple but _extremly_ variable
structure of almost everything within this systems. You just
entered a valid device address via two turning wheels and
hit the load button - no matter if it was a tape, a disk, a
card reader, a magnetic card reader, a punch tape reader or
what ever (later on even FD drives), the machine starts the
IPL from this device - just reads the first available block
and execute it - simple and powerfull - no boot manager, no
nothing, just any device - you could run the computer just
with card reader and card puncher (if you wanted to have an
output :).
As an aside, the Philips P850 series have machine-code
bootstrap tapes
that only use printable characters. A single (16 bit binary) machine word
is stored as 4 characters on the paper tape. The requirements are :
1) There must be at least one hole punched per character, apart from the
leader which is all nuls
2) the lower 4 bits of the character are the binary encoding of that nybble.
Talking about paper tapes ?
That's all. I normally use the characters @ to O
when I write tapes.
Philips tapes use 0-9 and J-O I think.
This machine, therefore will boot from a tape
containing only a subset of
all possible punchings. And I can well believe some card-based machines
would do the same.
At least /360, /370ish machines want binaty data from
boot devices.
> > Anyway, a 'byte', or more
particularly a character, is not necessarily 8
> > bits. It may be _now_, but it wasn't then.
> I love your comments (and I guess you had also
some contact with
> these 9 Bit Byte Bull Mini computers :)
I've come across enough machines that use 6-bit
characters internally....
6 Bit ? thats new - I never have seen a 6 Bit byte computer - I
know 6 Bit only from some serial line encodings.
Servus
H.
--
Ich denke, also bin ich, also gut
HRK