There is a large range of accessories available for laser printers, some models are better supported than others, and some models of laser printer have become so popular that some accessories are made by third-party manufacturers in addition to the "official" accessories provided by the original manufacturer of the printer.
Additional paper trays are available for most personal, office and workgroup printers. Paper trays are usually available in a range of sizes to cover the common standard paper sizes used throughout Europe and North America, such as Letter (8.5" x 11"), A4 (210 x 297 mm), Legal (8.5" x 14"), Eurolegal (8.5" x 13") and A5 (148 x 210 mm). Adjustable paper trays are available for some printers, these can take a variety of sizes. In general adjustable paper trays do not feed the paper are reliably or accurately as fixed-size paper trays, so a fixed-size tray is preferable for heavy use.
On a printer with only one or two paper input feeders it is often necessary to reload trays when a different type of paper is required, for instance headed paper for company correspondence, high quality paper for sales literature etc., so many users choose to purchase additional trays which they keep ready loaded with the different types of paper they use.
Most personal and office printers offer the option of a second paper feeder which attaches to the bottom of the printer and allows a second paper tray to be loaded. This greatly increases the paper capacity of the printer, reducing the frequency of paper reloading, and also permits two types of paper to be loaded at the same time. The latter feature is particularly useful when using headed stationery, as many word-processing packages allow the user to specify that the first page of a document is fed from one feeder (normally containing the headed stationery), and the remaining pages from a second feeder (usually loaded with plain paper).
Some of the larger office printers, which may also be used as small workgroup printers, offer the option of a high capacity feeder holding around 1,000 sheets. This mechanism is normally as large as the printer, and usually attaches to the front of the printer, replacing one of the paper trays. On a few printers the high-capacity feeder inserts paper via the manual feed slot, which allows the standard paper trays to be retained.
Envelopes provide a problem on many small printers, as they are only used intermittently and are difficult to feed. Some models of office printer offer an envelope feeder as an accessory, this device will accept a small stack of envelopes (between 20 and 50), and inserts them through the manual feed slot. The manual feed slot cannot be used for other materials when the envelope feeder is attached, but the envelope feeder is still a very useful accessory for users who print large quantities of envelopes as they are sometimes difficult to insert accurately into the manual feed slot.
A few advanced word-processing packages offer the ability to automatically address and print envelopes using the destination address information in a letter, in this context an envelope feeder can be particularly useful to a busy correspondent.
Large production printers with adjustable feeders will normally handle envelopes without much trouble, but most recommend the use of envelopes designed to pass easily through a laser printer.
Optional duplex units are available for many, but not all, office printers. The duplexing mechanism normally attaches to the printer in place of the face-up (auxiliary) paper output tray, and can significantly increase the operating space required by the printer. When operational the duplex unit receives a sheet of paper when the printer has printed the first side, and turns and re-feeds the paper for the second side to be printed. The feeding accuracy (registration) of many small printers is not perfect, so the images on the two sides of the paper may not align exactly. This can be annoying when using lightweight paper through which the image on the obverse side is discernible.
The laser printing process normally distorts paper temporarily, particularly the heat and pressure applied by the fuser, so the second side is printed on paper which is less than perfect, and may be curly or slightly creased. This in turn raises the incidence of paper jams, which are more common in duplex mode than in simplex mode.
The larger office printers, and some workgroup printers, offer the ability to attach an output stacker. The stacker takes the printed paper from the printer and, depending on the type of stacker, either puts it into a high capacity output tray, or into a collation mechanism.
The high capacity output stacker is a useful feature for long print runs in conjunction with a high-capacity feeder, as it reduces the requirement for frequent operator intervention and allows the printer to run unsupervised for long periods. If the stacker provides a job offsetting capability it will also be useful in a shared printer environment.
The collation mechanism is a sophisticated job separator, which provides multiple output trays, commonly 10 or 20. A print job can be directed to any of the trays, allowing different jobs to be separated (a tray could be allocated to each user), or alternatively, parts of a print job can be directed to different trays (for an invoice the accounts copy, the delivery note and the customer invoice could each be directed to separate trays).
Where multiple copies of a document are required, by using a collation mechanism each copy can be delivered to a separate tray. In this way efficient multi-copy printing is possible without a job spool, as the printer can print several copies of page 1, each to a different tray, followed by several copies of page 2, and so on.
Collation mechanisms are mechanically complex, and thus prone to jams and failures. They are necessarily physically large, and are usually designed to mount underneath an office printer, converting it from a desktop printer to a floor-standing one. A few collation mechanisms also provide extra paper input feeders.
Memory is a major component in the printer controller. It holds the "bitmap" (the array of dots which forms the image), the raw data and commands sent by the computer, and fonts, forms and graphics. The more memory a printer has, the more of each of these it can hold at once, so if many fonts are in use, or if a document includes many graphics, extra memory can be an essential add-on to a printer.
A printer with a lot of memory can hold more data sent from the computer, allowing the computer to send the data faster, and thus be free for more work sooner. Some printers may also print faster when equipped with extra memory, as additional memory can allow the controller to prepare the bitmap for one page while the previous page is being sent to the print engine (adding memory will not increase the maximum speed at which a print engine can print, merely the frequency with which it achieves the maximum speed).
Many personal and office printers are supplied as standard with only sufficient memory to print ordinary text documents. As graphics require a lot of memory in the printer, they may not be able to print large graphics, or may have to split a page over two sheets of paper, unless they are equipped with extra memory. On many personal and office printers extra fonts are held in memory, reducing the amount available for graphics. Extra memory is often essential for sophisticated applications such as charts, presentations, and desktop publishing.
Memory is normally supplied on a printed circuit board which plugs into the printer controller. On some printers this printed circuit board is of a design proprietary to the printer manufacturer, on others the industry standard memory modules designed for personal computers can be used. A few older printers require the insertion of individual memory chips into sockets on the printer controller. Most printers can be upgraded by the user, but as the process involves handling the delicate printer controller electronics, printer suppliers and dealers will normally perform the upgrade on request for a small charge.
The printer controller is basically a dedicated computer, and as such it requires access to stored information. On small printers this information is normally stored in ROM, but users who require many fonts, such as graphic designers, may require extra storage space. A few office printers, normally high specification printers using the PostScript page description language, offer the ability to add a hard disk for the storage of fonts.
The hard disk is normally supplied in its' own box, with its' own power supply, and attaches to the printer via a cable. Most printers which allow the use of an optional hard disk use a SCSI interface to talk to the disk. Hard disks using SCSI interfaces are available from a wide range of suppliers, some are designed exclusively for use with a particular brand of laser printer, others are intended for use with a personal computer such as the Apple Macintosh but may work perfectly well with a printer.
The optional hard disks available for office printer do not normally allow the printer to spool print jobs, job spooling is normally only available on printers which have the hard disk built in as part of the basic design.
The majority of printers are supplied with a Centronics parallel port and an RS232C serial port. While these connections are sufficient for most individual users, some users have special requirements, either because the type of computer they use does not support the normal parallel and serial ports, or because they want to use a network connection or other printer sharing system.
Computer interfaces are discussed in detail later in this book, but is appropriate to mention them here. Personal computers (P.C.s) generally fall into two categories, IBM compatible, and Apple Macintosh compatible. IBM compatible computers normally use the Centronics parallel port for printing, but they may also use an RS232C serial port. The Macintosh compatible computers normally use Appletalk, a communications protocol which is proprietary to Apple Computer Corporation. Other less common personal computers and workstations may use either the RS422 serial communications interface, or a SCSI interface.
Minicomputers support a range of interfaces, including the standard Centronics parallel port and the RS232C serial port. Some minicomputers use a Dataproducts parallel port, which is an alternative to the Centronics port. IBM System 34, 36, and 38 minicomputers, and IBM AS/400 minicomputers, use the IBM Twin-Ax communications mechanism, which includes communications connectors and protocols which are unique to IBM.
Mainframe computers have a wide range of interfaces, almost every mainframe computer manufacturer has their own high-speed communications port. IBM are the dominant supplier of mainframe computers, and so most production printers provide an IBM 370 Channel interface (commonly called "bus and tag"). There are several converters available from production printer manufacturers to interface between other mainframes and the bus and tag system.
In addition to the high speed interfaces, mainframes have ordinary communications interfaces for communication with terminals and low speed printers. The majority of mainframe manufacturers use RS232C serial ports for this purpose, however IBM use a proprietary 3270 Co-Ax mechanism and protocol for local connections, and a proprietary serial mechanism for remote connections.
Many computers are connected to a network, there are several physical types of network, the most common being Ethernet and Token Ring. The network provides a physical connection between computers, but to communicate via this connection a network communications protocol is required. There are several different network protocols available for each type of network, and in some large installations a network may be running several protocols over one physical connection.
Some users want to share a printer, but do not want the additional expense of setting up a network. In order to support these users some printer manufacturers supply a multi-user interface card which will allow several personal computers each to be directly connected to a printer. There are also separate printer sharing devices, these allow several computers to connect to the printer sharing device, which automatically switches between users and is in turn connected to the printer.
Obviously communications is a complex topic, but there are adapters for most printers to most communications systems. Many of the common communication systems are supported by the printer manufacturers, who supply add-on cards which insert into the printer and provide the required communications facility. Other communications schemes are supported by small interface boxes which convert a communications protocol into Centronics parallel or RS232C serial for use with a standard printer. Most network interfaces support one type of physical connection, and several of the most common network protocols. Some workgroup printers allow the use of several network interfaces so that they can be connected to several networks simultaneously. Because of the complexity and variety of communications options, persuading two different computers to talk to each other can be a very difficult task, similar problems can apply when making computers communicate with printers.
Each printer has a language of commands which is used to format the data sent to it. There are several printer languages in use, some are common throughout the computing industry and have become de facto standards, others are proprietary to a particular manufacturer. It is common for printer manufacturers to include several different printer languages in their printers, allowing their printers to emulate printers from other manufacturers, so a printer language is often called an "emulation", as it emulates the behaviour of another brand of printer.
In addition to the printer languages built into a printer, most manufacturers offer languages as add-on extras. These may be contained in ROM cartridges which plug into the printer, or in modules which plug directly onto the printer controller. The optional languages for a printer normally expand the capabilities of the printer, enabling it to print more complex documents, for instance most printers using an Escape Code language can be upgraded with an optional Page Description Language (PDL). As the printer controller is designed for the capabilities of the built-in languages, the more complex add-on languages often work rather slowly and are therefore intended for occasional use where the built-in language is not sufficient, rather than full time use.
As a way of overcoming the performance shortcomings of add-on printer languages a few manufacturers supply "co-processors" or printer controller upgrades which speed up the controller and allow the printer to run at a reasonable speed with the optional language.
A printer driver is a software program which resides on the computer using the printer, rather than the printer itself. The purpose of a printer driver is to give the computer an understanding of the capabilities of the printer, so that all the printer features can be used. Most software applications are supplied with printer drivers for the popular models of printer, but specialist software packages and less common printers may need printer drivers to be provided separately.
The printer driver will normally tell the computer what printer language the printer uses, which fonts are built in, how many paper feeders it has, what sizes of paper it can support, whether it can print duplex, and so on. If a computer software package does not have this information it cannot make full use of the printer, or send the commands required to control the features of the printer.
Manufacturers of the less popular printers usually produce printer drivers for the most common applications, but they are often unwilling to produce drivers for the specialist and less popular packages or for old packages. Because of this, printer drivers provide a long term support problem, the majority of applications packages are upgraded frequently, and the printer driver designed for an old version of the application may not be suitable for the latest version. It is often better to have a popular printer which the software supplier provides drivers for, rather than a rare printer which has to be supported by the printer manufacturer.
Fonts are one of the most important upgrade options for printers. Most printers are supplied with a basic range of fonts built-in, sometimes this is only three or four fonts, in some printers there may be forty or more fonts as standard. While the basic fonts supplied with a printer are adequate for many users, a large number of users require additional fonts. This may be because their corporation has standardised on a particular font for documentation and correspondence, or it may be that the nature of their work, such as graphic design, requires access to a wide range of fonts.
Fonts come in two types, bitmap and outline, and are normally supplied either on ROM Cartridges which insert into the printer, or on computer media (disks, tapes etc.) which are used with a computer to send (download) the fonts to the printer.
Bitmap fonts are fonts where each character is represented by an array of dots (a bitmap). This kind of font is common on older printers and cheap personal printers because it requires very little processing power from the printer controller. Bitmap fonts are often used on production printers for the same reason, as a production printer works very fast it cannot waste processing time manipulating the fonts.
As an array of dots the bitmap font is not very versatile. It cannot be scaled to different sizes, and can only be rotated through 90° intervals (in theory bitmap fonts can be scaled and rotated to odd angles, but the effect is usually visually unacceptable).
Because they cannot be scaled, printers using bitmap fonts require a different font for each size of type required, so a 10 point font and a 14 point font are two separate items (each requiring memory in the printer) Some older printers are not even able to rotate bitmap fonts through 90°, so they require separate fonts for portrait and landscape pages.
Outline fonts are fonts where each character is represented by a set of equations which define the lines making the character. Outline fonts (sometimes called contour fonts) are used by most modern office and workgroup printers, and by the more expensive models of personal printer.
As a set of equations the outline font is very versatile. It can be scaled to any size, so only one font is required for a typeface irrespective of size, and it can be rotated to any angle. This manipulation requires a significant amount of processing power which has only recently become affordable on most office printers. Once the outline has been scaled to the required size and rotated to the desired angle it is filled with dots and temporarily stored as a bitmap ready for printing.
Fonts for office and personal printers are often supplied in ROM cartridges. Both bitmap and outline fonts may be supplied this way, and as most cartridges can hold several fonts, the fonts are normally grouped together in useful "collections". Fonts stored in cartridges cannot be changed, you cannot decide to remove one font from a cartridge and replace it with another, so cartridges are not a versatile means of storage, however as the fonts are stored permanently in the cartridge, they do not disappear like downloaded fonts when the printer is switched off.
The pre-packaged collections of fonts supplied in cartridges by printer manufacturers do not suit all users. In order to overcome this, specialist font suppliers (such as a font bureau) are normally able to make custom cartridges containing the particular fonts a user requires. Font bureaux are also able to make special fonts containing symbols, for instance it may be useful to have a company logo as a symbol stored in a cartridge.
The alternative method of supplying fonts for printers is to supply them on computer diskettes (or tapes for mainframe computers), so that the computer can send (download) them via the communications port to the printer, where they are held in the printers' memory, or stored on the printers' hard disk. Both bitmap and outline fonts can be supplied this way, and the user can download the fonts required to the printer as required. Many modern application programs automatically download the fonts they need to the printer without the user ever being aware of the process.
The primary disadvantage of downloaded fonts is that if they are held in the printers' memory they will be lost when the printer is switched off, and need to be downloaded again when the printer is switched back on. This problem can be overcome by having a printer equipped with a hard disk on which the fonts can be stored.
A few office and workgroup printers offer the user the ability to add a facsimile option, a card which plugs in to the printer controller, and allows the printer to send and receive faxes. The facsimile transmission capability of this option allows faxes to be sent without being first printed out and then rescanned by a separate fax machine, so the quality of the fax seen by the receipient is often better than a conventional scanned fax. The other major benefit is in facsimile reception; the facsimile option allows the printer to receive faxes and print them on the laser printer mechanism, thus combining the functionality of laser printer and high-quality plain-paper fax machine, at a considerable cost saving over purchasing the two pieces of equipment separately.
The quality of an electronically transmitted fax (one which has not been scanned by an ordinary fax machine) is often very impressive. Electronic fax transmissions do not suffer from skew caused by inaccurate feeding of the paper into the fax scanner, so lines are shown more clearly, without the jagged steps often seen on faxes. As a facsimile option converts a printer into a dual-purpose machine, it may not be suitable for users who spend a lot of time printing.