Re: [9fans] HP: Printing with the Illiterate

[Russ Cox <rsc@swtch.com>]

On Fri, Aug 14, 2009 at 5:37 PM, J.R. Mauro<jrm8005@gmail.com> wrote:
> IJS is probably it; that's the PCL driver for the home-office class printers.

IJS is not PCL.

IJS is a custom protocol that is spoken between a bitmap-producing
program like Ghostscript and a bitmap-printing program like /usr/bin/hpijs
http://svn.ghostscript.com/ghostscript/branches/mtrender/ijs/ijs_spec.pdf

/usr/bin/hpijs speaks IJS to Ghostscript (or whatever is on standard
input/output) and speaks a new HP protocol called LIDIL to the printer
on the other end.  Rather than commit to a full specification of LIDIL
and have to worry about backwards compatibility in the future,
HP chose to use IJS as a shim protocol and distribute a binary
that talks to the printer (source is available but it's still a binary).

PCL is not in the picture.  Getting PCL out of the picture is exactly
the reason that IJS and LIDIL were introduced, because LIDIL is
basically "here is a bitmap" whereas PCL is a real language that
requires actual memory and computing power inside the printer.
LIDIL moves the memory and computing requirements out of
the printer into the computer proper.

Russ