CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [384]
Sensors and Switches Every laser printer has a large number of sensors and switches spread throughout the machine. The sensors are used to detect a broad range of conditions such as paper jams, empty paper trays, or low toner levels. Many of these sensors are really tiny switches that detect open doors and so on. Most of the time these sensors/switches work reliably, yet occasionally they become dirty or broken, sending a false signal to the printer. Simple inspection is usually sufficient to determine if a problem is real or just the result of a faulty sensor/switch.
Solid Ink
Solid ink printers use just what you’d expect—solid inks. The technology was originally developed by Tektronix, whose printer division was acquired by Xerox. Solid ink printers use solid sticks of nontoxic “ink” that produce more vibrant color than other print methods. The solid ink is melted and absorbed into the paper fibers; it then solidifies, producing a continuous-tone output. Unlike dye-sublimation printers, all colors are applied to the media in a single pass, reducing the chances of misalignment. Solid ink sticks do not rely on containers like ink for inkjet printers and can be “topped off” midway through a print job by inserting additional color sticks without taking the printer offline.
These printers are fast, too! A full-color print job outputs the first page in about six seconds. Of course, all that speed and quality comes at a price. Xerox’s base model starts at about twice the cost of a laser printer, with the expensive model selling for about six times the cost! Solid ink printers become a bit more affordable when you factor in the cost of consumables. A single stick of ink costs about as much as an inkjet cartridge, for example, but with a print capacity of 1000 pages, that completely beats the cost of inkjet cartridges over time.
Printer Languages
Now that you’ve learned about the different types of print devices and techniques, it’s time to take a look at how they communicate with the PC. How do you tell a printer to make a letter A or to print a picture of your pet iguana? Printers are designed to accept predefined printer languages that handle both characters and graphics. Your software must use the proper language when communicating with your printer, so that your printer can output your documents onto a piece of paper. Following are the more common printer languages.
ASCII
You might think of the American Standard Code for Information Interchange (ASCII) language as nothing more than a standard set of characters, the basic alphabet in upper and lowercase with a few strange symbols thrown in. ASCII actually contains a variety of control codes for transferring data, some of which can be used to control printers. For example, ASCII code 10 (or 0A in hex) means “Line Feed,” and ASCII code 12 (0C) means “Form Feed.” These commands have been standard since before the creation of IBM PCs, and all printers respond to them. If they did not, the PRT SCR (print screen) key would not work with every printer. Being highly standardized has advantages, but the control codes are extremely limited. Printing high-end graphics and a wide variety of fonts requires more advanced languages.
PostScript
Adobe Systems developed the PostScript page description language in the early 1980s as a device-independent printer language capable of high-resolution graphics and scalable fonts. PostScript interpreters are embedded in the printing device. Because PostScript is understood by printers at a hardware level, the majority of the image processing is done by the printer and not the PC’s CPU, so PostScript printers print faster. PostScript defines the page as a single raster image; this makes PostScript files extremely portable—they can be created on one machine or platform and reliably printed out on another machine or platform (including, for example, high-end