Re: Does PostScript Printer forget Data sent to it?

Robert Bonomi wrote:

As a practical matter, the _parallel_port_ (which the OP specified was
the method of connection for his printer) is a *unidirectional*port* on
the printer. input only. Thus "no way" accurately describes an attempt
to get _anything_ other than status-line signals from the printer back to the host computer.

Where the printer connection is bi-directional -- serial port or network
connection, for example -- then you have a 'reverse communications channel'
that can carry data back to the host computer. In _that_ scenario, you
have to look at what can/cannot be done within the language, and the
'PostScript run-time environment'.

Modern parallel ports ARE bidirectional. I've had lovely PJL
conversations with Lexmark Optra printers. Haven't tested PS, but
I see no reason PS output/errors would not come back as well.

Note BTW, that PJL has file access operations, but I don't know if
they could be used to get at temporary spool files on printer disk
(or disk-like) memory. Never played with them.

There is no provision in the language for copying even _that_ kind of
data back 'up' to the host computer. All you can do is read from disk
into printer RAM memory, and then use diagnostic commands to display
(over a bi-directional comm link) that data. And then you have to have
'something' that will interpret the diagnostic output and re-construct
the actual font/form data.

I dunno, I've seen the CUPS spooler send PS which causes a printer to
generate programmatic output back from the printer to itself, so it
seems feasible that if a PS program can get it's hands on some data,
it can send it back to the host.

(The elicited feedback was highly inappropriate because in that
installation, CUPS was not the final spooler!)

PostScript was fairly carefully designed, from the ground up, to _not_
have 'accidental' leakage paths between jobs. "Data sharing" is possible,
but only by explicit effort on the part of _both_ jobs.

It would seem that how much of the hard drive is exposed to PS by the
printer designers would have a lot do do with this.


In summary, I repeat my previous: 'You're worrying over nothing." <grin>


s/worrying/probably worrying/ :-)

(But I'm no expert...)


--
Clem
"If you push something hard enough, it will fall over."
- Fudd's first law of opposition
.

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