Introduction

[ Back to Contents ]

The History of Printing in UNIX

In the beginning of human history, knowledge was passed from person to person and generation to generation through direct, spoken communication. Over the millennia this knowledge transfer has changed from drawings on walls of caves, stone tablets, scrolls, and finally flat, printed, paper. Improvements in communication have driven technological and social change.

Throughout the history of computing, printed communication has played a major role in the development and improvements in computers and peripherals. It is not surprising, then, that in the early days of UNIX the first killer app was a word processor. With word processing, lawyers, academics, journalists, and scientists were able to better communicate. The line printer daemon ("LPD") was developed to spool and send the print files to the printer. Originally developed for communication with text printers, LPD can send any kind of file to a printer. Later incarnations of UNIX added a new line printer system ("LP"), which was incompatible with the old LPD but supported options for print jobs and filtering of the job files. However, very little has changed for UNIX printing over the 30 years since UNIX was first created -- applications produce output suitable for the printer, and the spooler sends this file to the printer.

Printing from Personal Computers

When the IBM Personal Computer appeared in 1981, it duplicated the UNIX printing model. Applications came with a certain knowledge of the escape codes and capabilities of popular printers, and users could tell those applications which codes to use for their particular printer. If you wanted to print files in the background, a "print" command was available that would spool jobs to a disk and print them while you worked on something else.

As printers began to support graphics, applications had to support numerous different command sets and capabilities, as well as mixed text and graphics. The complexity of the software used to communicate with printers soon began to rival the applications themselves, and it wasn't long before these "printer drivers" were an industry of their own. Unfortunately, a printer driver for one application rarely worked with another.

Apple's release of the Macintosh computer changed how printing was done on the personal computer. Designed from the beginning to be a desktop publishing system, the Macintosh abstracted the printing interface away from the application. Applications only had to tell the printing system where and what to print, and the printing system would translate that request into the desired output on the selected printer. Printer drivers were provided with MacOS or with the printer you purchased for your computer. The same driver supported all MacOS applications, and for a short time the Macintosh ruled the desktop publishing market.

Microsoft's first Windows operating environment duplicated this paradigm, and to this day printing and displaying information is handled almost identically in Windows and MacOS. Applications for these operating systems and others like NeXT and BeOS are able to produce professional-quality output with a generic printing interface, yet until recently UNIX has only had its print file spooling system.

The Evolution of CUPS

In 1993 a new company called Easy Software Products was formed. As one of its founders, my job was to develop a modeling program to build 3D images of aircraft, tanks, ships, and so forth. While developing this program I ran into a problem--how would we support printing of these models?

Applications in UNIX almost universally produce Adobe PostScript files for printing. PostScript is a computer language that describes pages mathmatically and is the language of choice for most high-end printers and imagesetters. PostScript is even used for display and was used by the NeWS window environment under the IRIX, NeXT, and Solaris operating systems.

However, PostScript is not generally supported by consumer-level printers and we certainly didn't have a PostScript printer in our office. At the time, Ghostscript (a popular free PostScript interpreter) was not an option, so we had to write our own printer drivers just as thousands of other companies have done before us.

I had written printer drivers before for the Radio Shack Color Computer and later the ill-fated MM/1 computer under the OS-9 operating system, so I took the code from those old programs and created and released to the public a program called topcl. Topcl took an RGB image file and converted it to HP Page Control Language (PCL) for a variety of HP and compatible printers. This combined with the tops program supplied with the IRIX operating system were enough to provide the printing support needed for our modeler.

Then one day a friend of mine visited our one-room office and I showed him our modeling program. During my demo he asked why we were trying to sell yet another 3D modeling program for IRIX, and why we didn't try selling the printer drivers. "After all," he said, "you had to develop drivers, don't you think other people need them, too?"

Not too long after this discussion, Silicon Graphics released a new printing product called Impressario. Impressario did many good things. It introduced the concept of filtering print files to convert them to a printable format. It included a PostScript interpreter to convert PostScript files to a raster format for non-PostScript printers, and it provided a common driver interface that could be used to develop printer drivers for almost any kind of printer. For all these good things, Impressario lacked printer drivers.

We released the first version of ESP Print in 1994, and by 1995 we stopped development of our modeling program to work exclusively on ESP Print. New releases of ESP Print included a modified version of Ghostscript that acted as a drop-in replacement for the Impressario PostScript interpreter, and we continued to add printer drivers as new printers became available. ESP Print was eventually ported to Solaris and HP-UX, and each operating system added a new wrinkle to an already complex software package.

In 1997 we started looking at supporting the Digital UNIX and Linux operating systems. Unfortunately, these operating systems used the original LPD for printing so you couldn't pass options to the printer drivers. This alone would cripple any drivers we might develop. To make matters more complicated, at least three versions of LPD were in common use, and they were not 100% compatible with each other. We knew then that we had to take the next step and replace both LPD and LP.

The original design of the Common UNIX Printing System (CUPS) was based around the LPD network protocol (see Figure IN.1). We added support for options and remote administration, and were just finishing the design of the new system when the Internet Printing Protocol (IPP) working group was created. The IPP working group originally was just going to update the LPD network protocol, but quickly changed its direction to create a much more functional and extensible protocol that could evolve as needed to support new technologies.

The switch to IPP probably delayed the release of CUPS by about 18 months, but I think everyone is happier for it. By supporting IPP, CUPS can accept and send print jobs almost anywhere. CUPS also provides the infrastructure needed to support modern printing and printers, something that printer manufacturers need to support their printers under UNIX.

FIGURE IN.1 The first design notes for CUPS.

Today CUPS is included with almost every major Linux distribution and is available freely for all UNIX operating systems. Printer drivers for CUPS are available commercially (ESP Print Pro) as well as from several free software projects, with quality often rivaling those under Windows and MacOS. Graphical printing interfaces for endusers and toolkits are also available in great numbers.

Finally, printer manufacturers now provide CUPS printer drivers for Linux, so printing under UNIX is no longer a thing of the past.

About This Book

This book covers every facet of the Common UNIX Printing System. There are four sections to the book covering the use of CUPS, the Internet Printing Protocol, programming for CUPS, and reference information on commands, functions, and configuration files.

If you've never used or heard of CUPS before, Chapter 1 "Introduction to CUPS," is the place to start. Here you'll learn how CUPS interacts with you, your printers, and your applications.

If you want to jump in and start using CUPS, use the CD-ROM at the back of this book to get you started. We've included as many of the popular CUPS-based printer drivers and interfaces as we could find!

Welcome to the future of printing under UNIX!

[ Back to Contents ]