PostScript, printer drivers and PPD

["Thomas Michanek" <thomas.michanek@xxxxxxxxx>]

Dear framers,

This is a bit off-topic, and doesn't concern FM directly.
Please direct all replies to me; I'll summarize to the lists,
if any such interest is shown.

Short version: What are the advantages of a "printer driver" and
PPD files in Windows/Mac, when such things doesn't seem to be 
needed on UNIX? How is PostScript generated on these platforms?

Longer version:
Even though I have used UNIX, Windows and Mac computers for many
years, one thing about printing has escaped me. I'm looking for
information on how PostScript is generated on different platforms,
and the possible advantages of using "printer drivers". If this
is explained somewhere in an existing document or book, feel free
to direct me to it, instead of answering my questions below.

My understanding is that before you can print any documents on
Windows/Mac, a "printer driver" must have been installed and setup
correctly in the Operating System. The printer driver can support
many different physical printers through the use of PPD (Postscript
Printer Description) files. The PPD files allow the user to select 
printer-specific features, and ensure that the correct Postscript
code is generated for these features for a particular printer.
To be able to use a physical printer, the printer has to be
"installed" in the system using the printer driver software.
During this process, the correct PPD file must be selected.

Then, when a document is to be printed to a printer on Windows/Mac,
my understanding is that it works like this:
1. You select the printer (physical or virtual) in the
   application's Print dialog.
2. You select/change possible options or features sypported by
   the printer (as determined by the corresponding PPD file).
3. The installed printer driver "interacts" with the PPD file for
   your selected printer, produces the Postscript code and directs
   it to the printer (or saves it to a PS file).

Questions:
A. Is it possible to have several printer drivers installed and in
   use simultaneously, such as both Microsoft's and Adobe's?
   If yes, how do the applications know what driver to use with
   what printer? If no, how do you switch between printers if they
   are supported by one driver and not the other?
B. Is it the driver that controls what printers you can select in
   the Print dialog, or where does that list come from?
C. For non-Postscript printers, like HP PCL printers, there cannot
   be any PPD files. How are printer-specific features handled?
   Can Adobe's printer drivers support such printers at all, or
   do these manufacturers have their own printer drivers?
D. How much of the printing code (PostScript) is produced by the
   application (e.g. FrameMaker), and how much by the driver?
E. Is it possible for applications on Windows/Mac to produce all
   Postscript code themselves, thus bypassing the driver and the
   PPD files, and then send the code to the selected printer?

The use of printer drivers and PPD files seem to offer the
possibility to customize the produced PS code for a particular
printer or a specific need. However, in my experience, a severe
drawback is that if you use an "inappropriate" driver, printer
or option when you print, the resulting PS code cannot be printed
(or distilled to PDF) because of incompatible or incorrect PS code.
I have many times encountered the problem that a produced PS file
cannot be printed when you send it to the "wrong" printer,
perhaps because you simply didn't know the final output device or
the correct PPD file at the time of producing the PS file.

Compare this with printing on UNIX, where there doesn't seem to
be any printer drivers or PPD files! You simply select a printer
name and print to it; no complex installation or setup.
Instead, the PS code is produced by the applications themselves,
and seems to be generic enough to suit all normal purposes.
I have sent PS files produced by UNIX applications to all sorts of
printers (including the Acrobat Distiller), and hardly ever had
any problems with files not being processed correctly. Perhaps I
haven't been using any "advanced" features, I don't know, but then
I haven't missed them either...

Additional questions:
F. Do "printer drivers" and PPD files exist in some form on UNIX,
   or must all PS code be produced by the applications?
G. Is it possible on Windows/Mac to produce "generic" PS code
   that will be processed without errors regardless of the
   final output device (including Acrobat Distiller)?
H. Those of you with printing experience from both UNIX and
   Windows, how often have you been in the situation that PS code
   produced on UNIX wasn't "good enough", so that you had to
   produce it in Windows with all the PPD features available?

Finally, PostScript files produced on UNIX are generally much
smaller than on Windows/Mac, when using the same document, the
same software (FrameMaker) and the same options. Even PDF files
are smaller when using the same version and options of the
Acrobat Distiller, and gives equal output quality. 
This combined with the fact that these files very seldom gives
any problems, especially compared to files produced in Windows,
makes me wonder whether whe whole idea of printer drivers and
PPD files really solves more problems than it actually creates.

I'm looking forward to feedback, preferrably in private email.


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Thomas Michanek, [Michagon], Linkoping, Sweden
Documentation Consultant, FrameMaker/UNIX expert
EMAIL:  mailto:Thomas.Michanek@telia.com
WWW:    http://go.to/framers , or go directly to:
        http://w1.133.telia.com/~u13304072/framers
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