It is almost axiomatic that thriving industries create their own jargon and nowhere is this truer than in the world of computers, where vendors borrow, adapt, and coin words seemingly on a daily basis. At some point, however, all the borrowing and punning creates confusion—especially for the people who want to use a technology.
Computer printer vendors have borrowed much of their unique dialect of acronyms, nicknames, and terms from traditional printing, but often put a different spin on the terminology. Apart from their marketing purpose, many of the predominant terms on a printer's specification page are useful clues that can help you choose the best device for your needs—if you can understand them. Here's a quick rundown of terms and concepts you need to know.
Resolution or DPI
Printers work by depositing tiny amounts of a colour (ink, toner, dye) on a surface like paper; each of these units of colour is called a dot—and the first thing that years of ads and marketing have taught us to look for on a printer's spec page is its DPI or dots-per-inch. This number tells us how many dots the printer is capable of fitting in a given space and, since the dots are the building blocks of text and pictures, a higher number is considered better.
You may wonder why printers have a much higher DPI than computer screens, where print commands originate: a typical inkjet these days easily exceeds 1000 DPI, while the iPhone 4's Retina display—probably the most pixel-dense screen available to consumers—barely makes it to 300 pixels per inch (PPI generally refers to monitor resolution, while DPI analogously relates to print resolution). The reason is that most printers can reproduce a very small number of colours — for example, a typical inkjet with four ink cartridges can produce a maximum of 16 colours for each dot (known as colour depth), while a single pixel on the screen is usually capable of displaying several million different hues.
On paper, therefore, special techniques such as half-toning or dithering are used to print adjacent dots in a specific pattern; because they are so tiny, once the brain perceives them, they are mixed into the intended colour, thus giving the printer a wider-ranging gamut than it is possible with just its four basic ink hues.
A matter of colour
When you compare printers, you must consider not only their ability to print dots in close proximity, but also how many individual colours they can print in any given dot location. Lasers and the less-expensive inkjets have only four ink reservoirs; at a given DPI, therefore, their colour depth will be lower than the more expensive inkjet models that sport five, six, or even seven different ink colours. Dye-sublimation printers offer the best quality for a given DPI because it can mix inks on the paper and thus provide a virtually limitless number of colours.
Keep in mind that the final print quality depends on a lot more than the DPI rating. Inkjets, for example, literally shoot liquid ink at your page; depending on the paper, the ink could be absorbed and bleed, causing blurry edges. A laser printer, by contrast, will usually have better edge contrast because it deposits toner on the page and then melts it into place.
Marketing gimmicks have also muddled the very concept of DPI. For example, you may see some printer manufacturer claim that its products have “optimised” DPI ratings obtained through a variety of techniques, such as passing the print head over the same location multiple times or printing dots of varying shapes. These normally result in a higher maximum print quality, but often at the expense of speed and ink consumption.
Finally, a quick look at your local computer retailer or online store will reveal that many printers have not one, but two resolution ratings — for example, 2400 x 1200 DPI. The first number indicates the horizontal resolution, while the second gives you its vertical counterpart. This difference is usually due to the printing head configuration and the underlying paper transport mechanics, which are designed to provide the right compromise of speed and quality to remain within the printer's final price range. In practical terms, your printer's driver will adjust the final output quality and you will not see a big difference.
Print speed is normally expressed as pages per minute (PPM). While this seems straightforward, unfortunately, there's no universal definition of what a “page” really is.
Most printer manufacturers tell you that their speed tests are based on a letter-size page with an ink coverage of five percent. The problem is that where that ink is located can dramatically affect the speed of some types of printers, while the complexity of the image and text printed could slow down some others.
For example, inkjet printers have a printing head that moves horizontally—thus, if the dots that make up the image printed are spread all over the page, the print head will have to move around a lot more than if the dots were concentrated in a single location, resulting in a lower speed. Laser printers, on the other hand, need to compose a physical representation of an entire page before they can print it; if the commands required to compose a page are particularly complex, it will take more time to output.
Different printing modes also result in different PPM ratings. Manufacturers typically provide values for colour and greyscale, especially in “multi-pass” laser printers, where the paper must take a longer path to print pages of the former type. The true variances, however, are often much subtler than that. You can bet that printing in photo quality will be slower than printing in draft mode — and that the PPM branded on the printer's box is unlikely to express the speed of the former.
Therefore, it is best to take the published PPM as an indication of the average speed of a printer—the higher, the better.
Another rating that you're likely to find in the context of printer performance is the duty cycle. This number expresses the number of pages of output per-month that a printer was designed to handle — typically, the manufacturer will start with this number as a goal and make a number of design decisions to satisfy it. These include the number and capacity of the paper trays, the efficiency of the printer's cooling system, the quality and resilience of its electromechanical components and so on.
Depending on its intended usage, therefore, a printer's duty cycle can vary considerably. Less expensive consumer inkjets could have a cycle of 3000 pages per month, while professional lasers can exceed 100,000 pages per month. When picking a printer, this number is only relevant in giving you a clue as to what kind of work it was designed to handle. Keep the duty cycle in mind as you evaluate other characteristics like ink cost and frequency of replacement, the price of maintenance kits and so on.
Much like a computer needs graphical memory to display images on a screen, a laser printer needs memory to interpret the commands that make up a page and create its representation so that it can print.
This makes RAM an important — sometimes critical— resource. Insufficient memory could result in the printer simply refusing to output a complex page, since it simply cannot compose it. Conversely, more memory will enable the printer to hold more information and speed up the printing process. By the same token, colour printers typically need more memory than their black-and-white counterparts, since each dot to be printed contains at least four times as much information.
Note that the amount of printer memory is tied to the size of a particular page, and not of an entire document. Therefore, a printer with 32MB of memory may be perfectly capable of printing a 100MB document, as long as none of its pages requires more than 32MB to represent.
In practical terms, making the right choice is as much art as science, and manufacturers have become quite adept at calibrating a printer's memory alongside its duty cycle: users who need to print more pages are also more likely to print complex documents and, therefore, require more RAM, or so the reasoning goes. Whether or not that is the case note that the RAM in most printers can be upgraded—although often at a much steeper price than computers.
Printers come in many varieties, but they all share a common problem: they need to talk to a computer, and this requires some agreed-upon protocol. In printer parlance, this protocol is called a Page Definition Language (PDL).
The two most popular PDLs are PostScript, which was developed by Adobe Systems, and Page Command Language, or PCL, which was developed by Hewlett-Packard. The latter was designed as a simple but flexible protocol whose main goal was to shift as much of the work to the computer as possible in an effort to keep printers simple and inexpensive. Adobe's solution, on the other hand, is a much more complex, but also a more powerful language designed primarily for printing professionals.
In the past, this meant that PostScript printers were significantly more expensive than their PCL counterparts, produced better and more consistent results, and were more widely supported (both OS X and Linux support Postscript natively). PCL printers were often cheaper, but originally designed to work with Windows and did not always include drivers for other operating systems. More recently, however, this distinction has become less relevant. The price of PostScript printers has decreased significantly, and almost every PCL-compatible printer now comes with OS X drivers.
These days, the choice of one PDL over the other is mostly relevant to industry professionals—from a consumer perspective, it's more important to ensure that OS X has the right drivers for the printer you want to buy and let the operating system take care of the rest.
There are, however, some protocol-related options that you should keep in mind when shopping. The first is Direct PDF Printing, which allows a PostScript printer to perform all the steps required to print a PDF document without any assistance from the computer. This eases network load and computing requirements, which can be quite onerous for complex documents.
The second technology to keep an eye on is Airprint, which will allow iOS devices equipped with version 4.2 of Apple's mobile operating system to print directly to compatible printers without having to connect through a computer. So far, only Hewlett-Packard has announced built-in support for Airprint in its ePrint lineup, but it stands to reason that other manufacturers will follow suit, or risk leaving a potentially lucrative market in the hands of a competitor.
As you can see, printer terminology is sometimes difficult to understand, with complex concepts often lurking behind the simple numbers that you find printed on boxes and manuals. With a bit of research, however, you can use the information that manufacturers provide to make a more informed decision the next time you are shopping for a printer.
Marco Tabini is a web specialist based in Toronto