Printers

The inner workings of laser printers and how to troubleshoot them, part 2

Do you troubleshoot laser printers? If so, you will find this Daily Drill Down by Faithe Wempen chock-full of important information. She gives you the lowdown on printer resolution, fonts, PDLs, drivers, and memory.


In part one, I explained how a laser printer works and what causes some of the more common problems that end users experience with them. In this Daily Drill Down, I’ll cover other laser printer-related features and technology.

Print resolution
Laser printer quality is measured in dots per inch, or dpi. In theory, a high-resolution printout will have sharper lines and less fuzziness. The first laser printers printed at 300 dpi, but nowadays 600 dpi is the minimal acceptable standard. Many good-quality laser printers often provide the option of printing at 1200 dpi.

Because a higher dpi makes a printer more expensive to manufacture and it requires more memory to print an average print job, many printer manufacturers have devised schemes to improve the print quality without cranking up the dpi. HP calls theirs Resolution Enhancement Technology (RET). The basic idea is to use smaller dots to fill in the jagged edges created when larger dots make a diagonal line, so the line looks smoother, but the dpi isn’t increased. Another name for this process is edge enhancement.

Printer fonts
A font is a particular typeface at a particular size. For example, Helvetica 12 point is one font and Helvetica 10 point is another. Further, adding bold or italic to the equation results in still another font, such as Helvetica 10 point italic. That’s the textbook explanation; however, many people these days use the terms font and typeface interchangeably.

There are several different types of fonts you can use for printing—fonts resident in your printer, TrueType fonts, PostScript fonts, cartridge fonts, and so on. To understand each of these and its place in printer history, let me give you a little background.

Back in the days when all programs were DOS based, each program had its own font files. Your word processor couldn’t use the fonts from your desktop publishing program, for example. I used Ventura Publisher for DOS back in 1988, which came with two typefaces: Dutch (similar to today’s Times New Roman) and Swiss (similar to today’s Arial). When I installed the program, it asked me what sizes of those typefaces I wanted. Then, it generated font files for each size and variant that I selected, with separate files for each combination of typeface, size, and attributes (bold, italic, bold and italic). Those font files took up a lot of space on my small hard disk! When Ventura Publisher was ready to print, it first sent the appropriate font files over to the printer and then sent the document to be printed using them.

Besides using these fonts on disk, you could also use any fonts that were built into your printer. For example, if your printer came with Courier 10 and 12 point and Helvetica 8 point, you could also use those in your documents from any program. That made printer-resident fonts very attractive, because any program could use them. However, the printer had only a few fonts to choose from. During this era in printer history, it was important to have a printer with slots that accepted cartridges so you could add more fonts. Back then, I had a 72-font cartridge for my printer, but because each typeface/size/attribute combination was considered a separate font, I probably had only three additional typefaces to work with.

During the same time, if you had $1,000 plus, you could purchase a PostScript printer. A PostScript printer had lots of built-in typefaces (35 or so) so you didn’t need the cartridges. You could also print PostScript-format graphics with a PostScript printer, a format popular with professional artists. Best of all, the printer used outline-font typefaces, which meant you could use them at any size without having a separate font file on your hard disk for each one. The printer kept an outline of what each letter should look like, expanded or contracted that outline, and then filled in the middle to form letters. At this point, PostScript was the only reasonable option for professionals who needed multifont desktop publishing capabilities.

Then, along came Windows 3.1, which introduced TrueType fonts. What a revolution! These TrueType fonts were outline fonts, like PostScript, that could be resized to any point size you wanted. They also worked generically with any Windows printer you installed, so a PostScript printer was not required. Sales of PostScript printers dropped dramatically because the primary reason people needed them went away. Every version of Windows since then has supported TrueType fonts, and the new Windows XP coming soon enhances the TrueType technology with a new type of font called OpenType that works basically the same way.

Page description languages
Your operating system and your printer must agree on a common language to communicate. This language, called a page description language (PDL), allows the computer to send a description of the page to be printed.

In the early days of printing, each printer brand (and each model) had its own unique PDL that no other printer shared. For DOS-based programs, a separate printer driver was required for each program. As you can imagine, managing drivers was a nightmare for software developers. They had to include hundreds of drivers with their program and issue updates to support the latest printers that kept coming out. (This was before the Internet, so there was not a good distribution channel for them!) Because of all this pressure, over time a few printer models emerged as the most popular, and other printers began to copy their PDLs. This was called emulation because one printer was pretending to be another so that it could use its driver. Printers were then able to be multilingual. They could speak their own language if the driver was available, and if not, they could work with any of two or three other emulation modes. Some features were not available in the emulation modes, however, so it was always advantageous to use the printer’s native PDL when possible.

The primary standard that emerged from this early shakeout was Hewlett-Packard’s Printer Control Language (PCL). Their original LaserJet printer used PCL 3. There have been many versions of PCL over the years, but you’d be hard-pressed these days to find a laser printer that is not capable of emulating some version of it.

There are other PDLs, but none are as pervasive in the laser printer community as PCL. For example, PostScript is another popular language, but only PostScript printers can understand it, and PostScript technology costs more. Therefore, most entry-level laser printers do not include it.

Printer drivers
The driver that’s loaded determines which PDL that a printer uses. In Windows, a single Windows-based driver serves for all programs, so you install the printer’s driver in Windows itself rather than through the setup program of a particular application. If you want to use a different PDL for a printer, set it up as a new printer in Windows and then switch between printers (that is, between drivers) in each application’s Print dialog box.

In Windows 95 and above, each printer driver includes user-definable settings for the printer. These fine-tune the relationship between the printer and the computer and tell the printer how you want certain things done. Some of the common settings you might see for a Windows printer driver include:
  • Network Sharing specifies whether or not the printer is available as a resource to other computers on your LAN.
  • Port Usage indicates which port is being used for the printer (for example, LPT1).
  • Spool Settings specify how (or whether) print jobs are stored on the computer’s hard disk and then fed to the printer. The printer accepts the print job based on the amount of memory it has available.
  • Page Order establishes whether a multipage print job prints first-to-last or last-to-first.
  • Default Page Orientation And Size sets Portrait or Landscape page orientation and a paper size (such as Letter) as the defaults.
  • Separator Pages indicate whether a blank sheet, or a sheet containing user information, prints before each job. (This can be useful when many people share a printer and the person tending the printer needs to know who should receive a particular printout.)
  • Font Substitution tells which printer-resident fonts, if any, should be used instead of other computer-downloaded fonts. (Setting up font substitution can make print jobs go faster because the fonts aren’t downloaded. However, the print results might not be what you expected unless the TrueType font you’re using is exactly the same as the built-in font in the printer.)
  • Graphics Quality/Halftoning determines the way graphics that include shades of gray will be rendered in black and white, and at what quality level.
  • Resolution sets the number of dots per inch to be used. (Higher settings mean better quality, more printer memory usage, and slower printing.)
  • Number Of Copies identifies the number of copies that should print by default. (This setting is tricky because you can set it for the printer and also within the Print dialog box for a particular application. The settings are cumulative, so if you set two copies in both places, you get four copies.)

These are just a few of the many settings you might find in a printer driver, and they depend heavily on the type and model of the printer.

Printer interfaces
In the early days, there were two printer interfaces: parallel and serial. Serial was much slower, but the cables could run across greater distances. (At that time parallel cables were limited to about six feet.) Some printers had both interfaces, but it was usually one or the other. Over time, serial printing became less and less popular; you’ll be hard-pressed to find a printer sold with a serial interface today. And although parallel is still the interface of choice, USB is becoming more popular due to its high speed, no-hassle setup, and ability to share the port with many devices at once.

A problem with the parallel interface, though, is that most computers come with only one parallel port, and power users typically have more than one device that needs to use it. Scanners and printers have traditionally had to share parallel ports, for example. To facilitate parallel port sharing, a variety of pass-through technologies have developed, but they don’t always work very well, even with BIOS setting adjustments. Sometimes turning off ECP and EPP support for the port in BIOS can make it “play nice” with a pass-through connection.

Printer memory
Every printer has at least a small amount of memory in it so it can hold the incoming data from the computer while it prepares itself to place data on paper. As I explained in part one of this series, there are two main types of printer technologies—those that print a line at a time and those that print a whole page. Laser printers fall into the page printer category. A page printer must have a considerable amount of memory. It needs more than just the few kilobytes required by an inkjet or dot matrix printer because the entire page must be held in the printer’s memory and then transferred.

A laser printer needs memory for the PDL it is using, for fonts, for page composition, for holding incoming data for the current page, and for queuing additional incoming pages. That’s a lot of different uses all competing for the same pool of memory! If you have problems with a laser printer running out of memory, adjusting any of those things can change the equation.

One factor that affects memory usage in a laser printer is the PDL that it uses. Different languages require different amounts of memory overhead. Because of that, you can sometimes switch PDLs and coax a printer to print a job it won’t print in another PDL. Downloaded fonts also occupy space in memory, so using printer-resident fonts can help a printer that’s low on memory eke by.

Another factor in the memory equation is the resolution at which you print. The oldest laser printers printed at only 300 dpi, so they didn’t need as much memory for page composition. Many of them came with only 512 KB. The minimum quality standard for today’s laser printers is 600 dpi, and because of that, the minimum amount of memory you will generally see offered in a laser printer today is 1 MB. However, back in the old days, those 512-KB printers would often run out of memory if you tried to do anything complex with them, and the same is true for today’s 600-dpi, 1-MB models.

Tip
Some printer drivers let you choose the resolution at which you want to print. If you are trying to solve an out-of-memory problem, try decreasing the resolution if possible.

So how much printer memory is enough? There’s no one standard amount. It really depends on the factors mentioned above, the types of print jobs, and the number of users being served. For personal use, I have a 600/1200-dpi Lexmark Optra S 1855 with 4 MB of memory and it has never hit a print job it couldn’t handle, although sometimes I have had to take it down to 600 dpi for a graphics-heavy page.

The more memory the printer has, the more pages it will be able to hold in queue waiting to be printed—and the quicker print jobs will offload from your Windows print queue. This might not be much of an issue on a single-user printer, but if you share your laser printer on a network, other people’s print jobs can become a drain on your system.

A large amount of memory in a laser printer can also improve the printer’s speed when printing graphical pages. That’s because many modern laser printers include compression technology that compresses data so that they can print a graphical page with less memory than would otherwise be required. When a printer has a lot of memory, it doesn’t have to go through that compression, so the page can print faster.

In addition, if you are working with a network-ready laser printer (one that can hook directly into the network rather than being shared by a PC owner), more memory in the printer becomes necessary. Some heavy-duty laser printers designed for network use even allow you to install a small hard disk in the printer that can hold queued print jobs while the printer catches up.

Conclusion
This Daily Drill Down rounded out the coverage of laser printer technology that I began in part one. I explained printer resolution, fonts, PDLs, drivers, and memory, and how each of them fit into the equation of laser printer performance. I hope that after reading my series, you’ll be able to select and troubleshoot laser printers with confidence!

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