On Thu, Mar 04, 2004 at 07:53:36PM -0700, ed sharpe wrote:
> we also had ones that would punch the really wide tape for the formatters
> for the line printer!
> I remember the tape being much wider though!
12-channel is common for that application
OnTopicTrivia: IBM protocols like HASP and 3780 allow you to send a
"skip-to-channel N" command to the printer. Your application (FORTRAN,
COBOL, etc) tells the printer to skip to channel 3, say, where you know
it's the right place for a customer address (for example). The printer
advances the carriage until channel 3 shows a hole, then prints from
wherever on the page it is. You can skip from channel to channel (changing
pages if necessary) to avoid having to put row-counts in your application.
You just load the paper tape to match your form, and things appear in the
right place.
So... by convention, "channel 1" is always punched to set the paper to the
top of form. Where, then, is channel 0?
Nowhere.
The protocol allows you to send a "skip-to-channel 0", but there is no
channel zero on the paper tape. The typical response from older hardware
is to empty the box of paper searching for channel 0 (newer hardware
treats it like a Form Feed).
Since we used to emulate IBM printers with COMBOARDs, I found and fixed an
interesting bug once... occasionally our customers would complain that our
product would hang if certain jobs were sent through. Turns out, the daemon
wasn't hanging - it was attempting to fill the disk with blank lines because
we received a skip-to-channel 0 command from the user's program. In other
words, we were trying to empty a virtual box of paper, but the disk was so
large that, before we could fill it, someone noticed that other jobs were
getting stuck and killed the process. I changed the array to *add* a zero
channel to our virtual paper tape (changed the array bounds from 1-12 to 0-12
and always wrote a "1" in location 0 - top of form) and the problem was solved.
Unlike a real printer, it's easy to make it a 13-channel virtual tape when it's
all software.
-ethan
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Received on Thu Mar 04 2004 - 21:19:38 GMT