"If you wish to understand a thing, you must call it by its correct name."

                                                Ancient Chinese Proverb

Technology is rife with jargon and acronyms, and the field of laser printers is no exception. Jargon and acronyms are not bad things; without them, communication about technical subject matter would be clumsy and convoluted. But when terms are ill-defined, when usage becomes overly loose and when acronyms lose all connection to their roots, we cross a line into gibberish.

An anecdote:

Some years ago, at a computer firm that shall remain nameless, there was a thing known as ASPI. As a newcomer to the company, the acronym was unfamiliar to me. I was constantly hearing about ‘ASPI this’ and ‘ASPI that’ and ‘ASPI the other thing’ and I was left wondering, “What on earth is ASPI?”. I could tell that it had something to do with printers, but exactly what was a mystery to me. Naively, I did what I thought was a reasonable thing — I asked people what ASPI stood for. Blank stares. Hostility. No one knew, and I had transgressed the corporate culture by inadvertently confronting them with their ignorance.

A little research (a peek at a glossary in the back of a printer user’s manual, as I recall), yielded
this — “ASPI: Asynchronous Serial Printer Interface”. So it wasn’t a mystical incantation, as I’d been beginning to suspect. Nor did it stand for Ambulatory Sasquatch Pelvic Implant. It actually made sense, and I could get on with making sense of the gear denoted by it.

And so this glossary is offered as an antidote to techno-voodoo and techno-babble, neither of which serve any good purpose in the workplace.

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A software program meant for a particular task; e.g. WordPerfect (word processing), QuickTax (income tax calculation). 'Application' must not be confused with 'operating system' (e.g. Windows. Windows is an operating system; applications run within it.). An analogy: if the operating system is the theatre, the application is the act on stage.


American Standard Code for Information Interchange. One of several data coding schemes, ASCII is the basis of virtually all character and control code systems currently in use in PCs and printers. Strictly speaking, ASCII is a seven-bit code yielding 32 control characters, 94 printable characters, 'space' and 'delete'. Many eight-bit extensions of the ASCII character set have been developed in order to increase the number of printable characters. These are properly called 'character sets' or 'symbol sets'.

Auto Continue

An item in the configuration menu of Hewlett-Packard's LaserJet printers. The Auto Continue setting determines how the machine will deal with recoverable errors. With Auto Continue set to OFF, a recoverable error will suspend printer operation and display the appropriate message, until the user intervenes by pressing the Continue key. With Auto Continue set to ON, a recoverable error will suspend printer operation and display the appropriate message for a period of ten seconds -- operation will then resume on its own. In either case, if the error was of a type that would cause a misprinted page, the machine will attempt to reprint the page.


Of a printed page; all of the area that is supposed to be blank. Opposite of 'foreground' (q.v.).

Background Charge

In Canon's laser printer engines, that level and polarity of electrostatic charge on the drum that is repellant to toner during the development stage. To put it another way, background charge is responsible for the whiteness of the background of a printed page -- insufficient backgound charge will cause a grey background. Commonly known as 'primary charge', we purposely use the term 'background charge' here to better convey the part it plays in the laser printing process. (See 'process polarity'.)


In rotating machinery, any arrangement for engaging/disengaging one rotating member with/from another.


Short for Cyan, Magenta, Yellow, Black; the primary colours used by laser and inkjet printers to render their colour gamut. ('K' stands for black because 'B' already stands for blue in the term RGB.) Strictly speaking, there are only three primary colours; cyan, magenta and yellow. In theory, mixing all three produces black (known as 'process black'). In practice, process black tends to be a very dark mud colour -- not satisfactory. That problem is solved by the presence of true black toner or ink in the printer.


A sufficiently high voltage applied to a conductor suspended in air brings on ionization of, and a net current flow through, the surrounding air. This discharge may be accompanied by a blue glow around the conductor. Both the discharge and the glow are known as 'corona'. Corona discharge is used in laser printers to generate the electric charges needed for background (primary) charge and for transfer.

Corona Wire

A fine wire strung down the length of a metal channel, electrically insulated from the channel and connected to a high voltage source. (See 'corotron'.)


'Corotron' is an old Xerox term for what is commonly referred to as a 'corona assembly' or 'corona wire assembly'. It's a useful term -- one word that unambiguously denotes a complete corona assembly.


Cathode Ray Tube. The imaging element of a computer monitor or television set. (See 'raster'.)

DC Controller

Hewlett-Packard's term for 'engine controller' (q.v.).


A particulate medium throughout which toner is dispersed. The developer in some early Xerox machines was a granular material, which was tumbled over a latent electrostatic image in order to develop it. More modern developers are iron particles, whose magnetic properties are exploited to create a 'magnetic brush' effect. (See 'magnetic brush'; 'toner'.) In some designs, one can make no distinction between ‘developer’ and ‘toner’; they’re one and the same thing.

Also, that portion of a printer that performs development, as in 'developer unit'.


That stage in the printing process where the 'latent electrostatic image' becomes visible, as toner adheres to the foreground charges on the drum. The result is called a 'developed electrostatic image'.


Software that's able to render an application's printer output into a form that's comprehensible to a given printer. It's wise to always make certain that the driver in use is the correct one for the printer. Using a 'close enough' driver can result in odd symptoms, or inability to use all of a printer's features.


The rotating imaging element in a laser printer; an aluminum cylinder (substrate) with a thin, uniform coating of a photoconductive material on its outer surface. The aluminum substrate is always connected to system ground. The photoconductive coating has the property of being an electrical insulator as long as it's kept in the dark; it becomes an electrical conductor on exposure to light. While in darkness, the drum’s surface can be given a uniform electrostatic charge (the ‘background charge’). Laser light is used to selectively dissipate the charge to form an invisible ‘latent elctrostatic image”.

Dry Ink

Toner (q.v.).


In printing, to print on both sides of a sheet of paper. Opposite of simplex, printing on one side only.


Electronic Industries Alliance, formerly the Electronic Industries Association. A standards-setting body.


1) Electric charges at rest; 2) The physics of electrostatic phenomena (like charges repel, unlike charges attract). Discharges of electrostatic energy are most commonly observed as either a nuisance (doorknob shocks and computer hiccups) or a lethal force of nature (lightning). In photocopiers and laser printers, electrostatic charges under exquisite control are put to work to form a printed page.


Electromagnetic Interference. Alternating current in any conductor creates an alternating magnetic field surrounding the conductor and radiating from it. That magnetic field can, in turn, induce currents or voltages in other nearby conductors, or it can influence other magnetic fields. An example of the latter case is the 'swimming' effect that occurs in a CRT display when an unshielded fan motor is in close proximity to it; the magnetic field radiating from the fan motor's windings interferes with the magnetic fields controlling the deflection of the cathode ray in the CRT.


Mimicry of a machine behaviour standard. A printer from any manufacturer that operates as if it were a Hewlett-Packard LaserJet is said to 'emulate' the HP LaserJet.

Encoder Sensor

A sensor whose output can be used by a microprocessor to monitor motion in a machine; e.g. rotation of a motor’s shaft.


Normally associated with power producing machines, the word 'engine' can also mean 'any mechanical contrivance'. In a laser printer, the 'engine' is understood to be the complete mechanism along with the electronics necessary to control its basic functions. That·does not include the electronics necessary to interface the engine with a computer and/or a user. (See 'engine controller'; 'formatter'.)

Engine Controller

The electronic circuit board in a laser printer that controls all the electromechanical functions involved in the imaging/printing process. In Canon's engines, that is everything up to and including the execution of an 'ENGINE TEST' printout (vertical lines). The engine controller has no provision for user interface (control panel), computer interface (communication ports) or interpretation of coded data to be printed. Those functions are provided by the formatter (q.v.).


ElectroPhotographic. Pertaining to the electrostatic imaging/development cartridge used in Canon's engines.


Pertaining to the particular electrophotographic cartridge used in the Canon LX Engine (HP LaserJet IIP/IIP+/IIIP).

Flux, Magnetic

Flux is a measure of magnetic force. This subject quickly becomes quite complex, far beyond the scope of this document.

Following is an extract from QMS Inc.'s User's Guide for the QMS PS-810 turbo and QMS PS-820 turbo. It is an excellent explanation of the distinction between the terms 'font' and 'typeface'.

- - -

"The following two words, 'typeface' and 'font' are two words you should know. Often confused, typeface is the larger category, while font is a subset of typeface.


Typeface refers to the style of the face of printing type. Typeface does NOT define a particular size, but only a "style" or licensed design.


A font is a complete collection of characters in one typeface all of one size, like 10-point Courier. Although you hear font used more generally, as if referring to a kind of typeface, a font is defined by being of the same style and size."


Of a printed page; all those places which are supposed to be black (or coloured in the case of a colour printing process). Opposite of 'background' (q.v.).

Foreground Charge

That level and polarity of electrostatic charge in a latent electrostatic image which is attractive to toner during the development stage.


The electronic circuit board in a laser printer that provides user and computer interfaces, and interprets print data and commands for the engine controller. The formatter's output to the engine controller is essentially a serial bit stream, analogous to the video data sent to a monochrome CRT by a computer's video controller.


In colour reproduction technologies, a 'gamut' is the subset of the full colour spectrum that a given process is capable of. Reproduction technologies have their limitations; e.g. CMYK cannot produce a brilliant crimson red.


Institute of Electrical and Electronics Engineers. Among other things, the IEEE formulates and publishes standards pertaining to the electronics industry.


A standard for the implementation of bidirectional parallel communications in what is commonly referred to as the Centronics interface. The Centronics interface has, for decades now, been a de facto industry standard for parallel printer interfacing. With the addition of bidirectional capability (not a feature of the original interface), the interface has grown considerably more complex. IEEE 1284 defines all aspects of it. Interface cables for use with current printers should be constructed in compliance with IEEE 1284.


Refers to page orientation. A landscape page's top and bottom are the long edges of a rectangular sheet of paper; i.e. oriented like a landscape painting. Opposite of portrait.


Light Amplification by Stimulated Emission of Radiation.

Laser light is notable for its coherence. In laser printers, a pinpoint beam of laser light is emitted by a laser diode. That beam of light is what ‘writes’ a latent electrostatic image on a photoconductive drum. The light is not visible to the human eye, and can damage the eye.

Latent Electrostatic Image

An invisible image of a page to be printed, formed in electrostatic charges. The development stage of the printing process renders the image visible.


A sheet of paper, as in a bound book. One leaf can hold two pages.


'Legacy' equipment/software/what-have-you is old stuff that the manufacturers wish you'd get rid of and quit expecting support for.

Magnetic Brush; Magnetic Brush Developer/Development

A magnetized metal roller carrying iron particles on its surface can be made to behave as a rotating 'brush' -- the iron particles stand on end, presenting themselves as 'bristles'. This effect is put to use as a means of applying toner to a latent electrostatic image in order to develop it. (See 'toner'; 'developer'.)


Multi-Function Printer. Typically, a printer with a flat-bed document scanner attached for copying and scanning. Often, the machine will have fax functionality as well.


Modular Input/Output. Often heard in the term 'MIO card'; i.e. a network connection card.


A laser printer with sufficient memory and/or a hard disk drive installed so that it's able to perform the mopier function; i.e. it can keep an entire document in residence and composed for printing multiple times at full print engine speed.


The word 'mopy' was cobbled together from 'MOP' -- Multiple Original Prints, and 'copy'. The word was meant to promote the idea of using a laser printer instead of a copier to produce multiple prints of a document for distribution.


Organic Photo Conductor -- the material used to coat the 'drum' (q.v). One presumes that the word 'organic' here is used in its chemical sense: "pertaining to carbon compounds".


A bluish gas having a distinct, bracing odour. Ozone forms when ionized oxygen atoms combine in threes, creating molecules of ozone (O3). Ozone is a by-product of corona discharge, i.e. electrical conduction through air. Ozone is toxic, corrosive and explosive. Laser printers that employ corona discharge elements (corotrons) for background and transfer charge creation generate ozone, and are equipped with ozone 'filters'.

Ozone Filter

A porous block of material that reduces ozone emissions from laser printers which generate the gas. Ozone is unstable, and at elevated temperatures it readily breaks down and reverts to oxygen (O2). At room temperatures, ozone breaks down more readily in the presence of a 'catalyst'. The ozone 'filter' is just that -- a catalyst that promotes the breakdown of ozone gas molecules to molecules of oxygen.


One printed side of a 'leaf' (q.v.).


Hewlett-Packard's Printer Command Language.


Portable Document Format


See "Drum".

Pickup Roller
Any roller whose job it is to get a sheet of paper started on its way into a printer’s engine. Not to be confused with a ‘feed roller’ or a ‘separation roller’. Pickup rollers can take a variety of forms. They often have a portion of their circumference flattened, or they may be only a sector of a circle. Sometimes referred to as a ‘pick roll’.


Refers to page orientation. A portrait page's top and bottom are the short edges of a rectangular sheet of paper; i.e. oriented like a portrait painting. Opposite of landscape.


IBM's Personal Printer Data Stream command language (originally called 'IBM ASCII').


IBM's Print Quality Enhancement Technology. Similar to HP's RET.

Process Polarity

'Process polarity' refers to the manner in which a given machine creates background and foreground. In photocopiers, the primary charge is attractive to toner; light-exposed areas become repellant to toner. In Canon's laser printer engines, the reverse is true: the primary charge is repellant to toner; areas exposed to laser light become attractive to toner. So, we can define two distinct process polarities for monochrome machines:

a) Light 'writes' white (photocopiers).

b) Light 'writes' black (most laser printers).


24 or 25 sheets of paper. Originally, four sheets of paper folded in half to form a 'booklet' of eight leaves. Also, any one of the sets of leaves which make up a bound book. (See 'ream'.)


A rectangular image field created by scanning a focussed beam of energy both horizontally and vertically. In a CRT display, the energy beam (a cathode ray; i.e. electrons) is modulated to illuminate the image field as needed to synthesize the desired image. In a laser printer, the energy beam (laser light) is modulated to 'write' a latent electrostatic image on the drum. Horizontal scanning in the laser printer is done by rotating a polygonal mirror in the horizontal plane. The rotation of the drum provides the vertical component of the scan.


20 quires -- 480 or 500 sheets of paper. In modern commercial usage, 500 sheets (standard package quantity). A 'printer's ream' is 516 sheets -- the extra number being allowance for setup waste.


Synchronization of the leading edge of a sheet to be printed with the developed electrostatic image on the rotating drum.


Resolution Enhancement Technology. At 300 dpi, diagonal line edges tend to reveal their 'dot matrix' construction by way of a 'staircase' appearance. With the LaserJet III, HP introduced RET as a way to get a 300 dpi engine's output to look just about as good as that from a 600 dpi engine. RET is implemented by logic on the formatter board; it does not affect memory requirements, nor does it complicate or slow down the composition of a page.


Radio Frequency Interference. Radio and TV transmissions are forms of electromagnetic energy (see EMI). Just as they induce electrical currents in receiving antennae, they can induce unwanted currents in virtually any conductor in their path, e.g. the controlling circuitry of a printer or personal computer. Such interference may cause the printer or PC to exhibit puzzling symptoms of erratic operation.


Short for Red, Green, Blue; the three primary colours of luminous displays like CRTs. Mixing all three produces white light.


Recommended Standard # 232 revision C. An elderly (1969) EIA standard originally drawn up to govern the connection (interfacing) of mainframe computer terminals to modems. The interface’s flexibility led to its adaptation to all sorts of interfacing tasks. Printers were often attached to PCs via an RS-232 interface. (One needn’t feel obliged to include the revision letter suffix in every mention of RS-232. In fact, the last time we checked, RS-232 was at revision D.) However, RS-232’s flexibility can be a curse, as there are so many ways to get it wrong. The ease of parallel interfacing, and the emergence of the USB are pushing RS-232 toward obsolescence.


a) A device for sweeping a laser light beam repeatedly along a straight path as it ‘writes’ a latent electrostatic image; i.e. a ‘laser/scanner’ assembly or ‘printhead’.

b) A device for capturing a digital ‘image’ of a document; e.g. a flat-bed scanner on a multi-function printer.

Lexmark’s term, ‘printhead’, is preferable to HP’s ‘laser/scanner’ assembly because it can’t be confused with meaning ‘b)’.


Any device for detecting a machine state or condition, or for monitoring the progress of a process.

Serial Interface

An interface method wherein data is transmitted and received sequentially, bit by bit. A practical serial interface can be implemented using only three wires; one for transmission, one for reception and one for a ground reference. See RS-232.


Single In-line Memory Module. A compact printed-circuit module used to package some quantity of RAM or ROM.


1) Any deviation from parallelism between the edges of a sheet of paper, and the boundaries of the text printed on it; 2) Any condition that results in skew. Paper skew appears at all four edges. Optical skew appears at the leading and trailing edges only.


Snap-fit is a form of interference fit where mating parts -- a printer's covers, for example -- are forcibly assembled.

System Board or System Card

IBM's term for an electronic circuit board that combines the functions of an engine controller and formatter on a single board. The IBM 4019 is an example of a printer equipped with a 'system board'.


Finely divided thermoplastic resins and coloring agents that form the ‘dry ink’ used in laser printers. There are many formulations.


That stage in the printing process where the developed electostatic image is transferred to the paper.


See 'Font'.


Universal Serial Bus. A serial interface hardware specification and protocol for computer/peripheral interconnection. Some of its features are:

- Hot plugability in both hardware and software terms. Attachment or removal of a USB device
to/from a running system should not damage or hang the system.

- Top speed of 12 Mbps (12 megabits per second), and a slower speed of 1.5 Mbps.

- Up to 127 devices permitted to share a single USB network.


A dry, electrostatic photocopying process invented by Chester F. Carlson of the United States in the mid-1930s. The word 'xerography' was constructed from ancient Greek words. It means, literally, 'dry writing'. The development of the laser diode and scanner made it possible to adapt the to image synthesis. Hence, the laser printer.

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