Page Formatting

Page Formatting in Laser Printers

The first laser printers were developed at Xerox in the early 1970s. The timing is contemporaneous with the first dot-matrix printers but the likely use for a laser printer seemed very different.   A laser printer is basically a photocopier with the page-scanning mechanism substituted by the laser, a polygon mirror to make it scan and a modulator like a high speed shutter to turn the beam on and off. The xerographic page is created by a stream of data controlling the laser beam. (Some early printers could photocopy part of a document such as the form and laser-print the data).

There isn't anything special that actually requires a laser beam, the light source could be any other pencil thin powerful beam made to scan using a mirror. In later machines QMS dropped the laser and used a projector lamp with the beam controlled by LCD shutters (it worked, just not very well). Oki has always used a pagewidth array of LEDs instead of a laser (it works so well others have been adopting it). The important thing is that a drum or belt of "photostatic" semiconductor that has been charged to a high voltage in the dark is selectively discharged, controlling where it will pick up toner powder.

A significant problem is making the page image. If the image were just lines of text the mechanism could be very like that used for a screen video display but instead of 25 lines of 80 characters something like 66 lines of 80 characters. Xerox Alto computers had a portrait oriented screen to show a page image matching the expectation people then had to see a page on the screen as they would on their desk. A page shaped screen matched and integrated well with the printer However to make sense of the laser printers cost and potential it probably needed to offer higher quality print than would be seen on the screen and more by way of graphics.

The PARC team that built the early machines used a DEC PDP-11/34 as the formatter. Creating the pages needed a fairly powerful computer and DEC's PDP-11 was a very popular machine, so it was used.

The new Xerox 9700 machine caused quite a bit of excitement. Apparently Burroughs had their badged version (the 9270) at the Hannover Messe of 1977.

Xerox (9700 - 120ppm )and IBM (3800) started shipping laser printers in the mid 1970s but these were expensive alternatives to fast lineprinters, not office printers. At 120 pages per minute and with a PDP-11 minicomputer inside it the 9700 was quite some machine. These machines clearly are the parents of modern laser printers but they are also very different -in a completely different class on both throughput and purchase price.

Xerox own print language XES (Xerox Escape Sequences) dates from around this time.

HP developed the 45 page per minute 2680A Laser Printing system in 1980, however priced at $120,000 (comparable with the HP 3000 mini-computer it partnered) it wasn't a mass market device. The print quality wasn't all that great either, 150 dots per inch. To provide this the development team developed a sophisticated formatter using bit-slice microprocessors to create the page using a linked list of cells, economising on the memory that would otherwise be required.

Likewise the 2687A printer launched a couple of years later was much smaller but at $12,800 still rather expensive.

Mass-Market

In 1983 Canon developed the LBP-8 laser printer engine.   This new engine was very different; much smaller and cheaper. Canon based the new engine on the personal copier they had developed so it also had a one piece cartridge to make maintenance easier. Canon's sales network had the expertise to sell and maintain photocopiers, not build and sell computer peripherals, so they looked for partnerships with computer companies.

Apple's LaserWriter was one example of the new engine.   Apple equipped it with a Motorola 6800 running at 12MHz, 1.5 megabytes of RAM as workspace to rasterise the image and 500 kilobytes of firmware holding amongst other thing a PostScript graphics interpreter. Apple priced this at $6995 - more than twice the price of the Apple Mac computers it complemented. It was expensive, five times the price of dot matrix printers at the time. What the LaserWriter could do was handle a whole A4/letter page with mixed text and graphics seamlessly at up to 8 pages per minute. The printers capabilities weren't completely unprecedented, professional typesetting machines had been offering these capabilities for over ten years using the Unix troff utilities. Typesetters were four or five times the price of the LaserWriter however. What was different was that Apple users drew what they wanted on the screen and printed it. Apple Macs and the LaserWriter swept through the graphics industries.

HP used the same Canon printer engine for the Laserjet. Because they used a simple approach HP were a year earlier to market. Laserjet was initially priced at $3495, and by September '85 at $2995. It had the less costly 8MHz 68000 used in the Apple Mac computers themselves and only 128 kilobytes of memory so it could only handle a small picture - not a full graphical page. Laserjets used a less ambitious graphical language which had been developed for HP dot matrix printers - PCL. The Laserjet may have been less ambitious but even more revolutionary because it was more affordable. A Laserjet printer would produce a piece of correspondence looking better than anything typed with very little noise. HP LaserJets and PCs with WordPerfect software became a standard in offices. Over the next few years HP sold 4 million of them, an unprecedented number until that time.

Canon, HP and Epson all introduced inkjet printers in 1984. The inkjet idea had been tried by Siemens in the late 1970s but printers had not proved reliable. HP and Canon were both looking for a portable equivalent of the dot-matrix and came up with the Thinkjet and the BJ-80 respectively, both with 12 nozzles to give them a bit of an edge over 9 pin dot matrix. They weren't very different from dot-matrix machines but the thermal printhead was lighter allowing the motors to be so. Epson took a rather different direction with the SQ-2000 which had 24 nozzles using piezoelectric ink ejection to give print they hoped would compete with daisywheel and laser printers. Early inkjets didn't perform terrifically well. Canon and HP printheads were intended to be so cheap as to be disposable, but they weren't that cheap. However HP management, in particular, seem to have been very confident that inkjets would shortly outperform both dot-matrix and laser printers.

Evolution of Print Standards

Through to the 1980s there was one fairly sure-fire way to attach a printer to a computer and that was to use RS-232. RS-232 is an EIA standard first introduced in 1962 and intended to control teleprinters over phone wires using modems. Since teleprinters were often used as printers it might seem at first glance that the standard would be ideal.In today's screen-oriented world it is easy to forget that the print industry was huge. Bell Labs could afford to develop UNIX and the troff suite of typesetting utilities because they would do a better job more cheaply than typesetting by hand. The machines were being marketed by Singer. computer aided typesetting.