Contents of this page:

  • Print Speed Limits
  • First Page
  • Print Process
  • Laser Printers
  • Inkjet Printers
  • Dot Matrix
  • Thermal Printers
  • Design Limitations

    • Print speed is one of the key characteristics of a computer printer.   In a business environment with tasks like printing invoices, catalogs or artworks a printer that is twice as fast might get twice as much done in the working day. Print speeds vary from about 1 page per minute for little colour inkjets to above 60 ppm for work-group laser printers.

    Related to this, but not quite the same thing is the printers time to act. People buying railway tickets don't want to wait ten seconds for the ticket machine to print a confirmation that they paid. Nor do people want to wait in shops for a receipt.   Some paperwork has to be ready on demand.

    Bigger, faster printers tend to have additional benefits. They are usually cheaper to run; the cartridges are larger - (lives of 25,000 pages rather than 3,000 pages). Whilst the cartridge itself may seem expensive the price per page will be lower. They also tend to need less attention and will be better at reporting issues to IT specialists over the network.

    The world's fastest laser printers at the time of writing (January 2011) are probably the IBM Infoprint 4000 series with a speed around 330 A3 images per minute - and in duplex configuration double that. The Océ Varioprint 6250 is somewhat slower - just 250ppm. Machines like these are exceptional, a couple of meters long in a basic configuration and needing a 3 phase power supply as well as a considerable data-source to keep them busy.

    Most mono office laser printers are limited to about 60 pages per minute and most colour printers are currently a bit slower. In 2010 Dell was claiming to have the fastest colour laser printer - the 7130cdn rated at 47 pages per minute.

    There are some fast inket printers as well, like HP's Edgeline and the new Memjet machines with 60 page per minute colour print.   Big inkjets often have their speeds measured in metres per hour rather than page per minute.

    See also

    • ISO/IEC 29183:2010 Method for Measuring Digital Copying Productivity of a Single One-Sided Original
    • ISO/IEC 24734:2009 Method for measuring digital printing productivity

    Print Speed Limits

    There have always been fast printers;   why are cheap printers slow?

    An obvious point is that laser, inkjet and dot-matrix mechanisms have some mass, so if they are going to move quickly they need substantial motors. It isn't just a matter of power, many of the motors in a printer need very fine control over their position. Powerful motors with fine positioning demands bigger motor driver chips, heatsinks and power supply unit.

    Paper feed may be a problem. Paper doesn't weigh much, but it is difficult to propel a 5 gramme sheet through a machine with accuracy better than a thousandth of an inch - which is what a 1200dpi printer is being asked to do. To handle more than a page per second might need tractor-feed, web-fed paper on rolls or vacuum-cup paper pickups.

    The least obvious problem was probably the greatest until very recently. What is on the computer screen is reformatted for printing. There is no point equipping a printer with more powerful motors and a fast laser scanner if the computer power to reformat the page wouldn't be affordable. Some recent low-cost printers are much faster than ten year old designs simply because fast processors and memory are now cheap.

    First Page

    An important aspect of print speed is the time to wait for a page. It might seem as though a 60 page per minute printer should produce a page in a second.   However some laser printers can take more than a minute to get the first page out. The printer has to accept the data, render the page and warm up the fuser before the first page emerges. In some circumstances this would be critical - producing receipts in a shop or shipment notes on a picking line for instance.

    Canon and HP have an advantage in laser printer speeds because the "instant on" fuser they use comes to temperature in under ten seconds allowing the printer to wake up from power save and print almost immediately. Dot-matrix and thermal printers don't need a warm-up. Some inkjets might take time to clean the printheads.

    Once they reach temperature laser printers should run pretty much in accordance with their headline specification, so a 30 page per minute printer usually delivers about 25 pages of a report a minute after the computer said print. If they don't do that its usually a memory problem

    Some printers have extraordinary strartup times. The Tektronix Phaser 360 too 20 minutes to heat up, consuming a third of a colour ink-stick doing so. It also needed 30 minutes after shutdown before it could be moved, to allow the ink to solidify. Basically you might say its warm up time was so long and consumed so much ink that it no longer counted - it wasn't going to be turned off.

    Information held in computers is usually a mixture of numbers, indexes, text, font specifications, vectors and bitmaps. Each kind of data has different properties, how they are interpreted depends on the application (program) that owns the area of main memory they are in. Applications in turn call on a set of system libraries.

    Screen and print are both interpretations of this internal representation. So what looks like a typewritten page is a window on the screen created by the graphics subsystem.

    From the mid 1980s onwards almost all screens have been "bitmaps", sometimes known in print literature as "rasters". The screen is basically a fine grid of picture elements or pixels. A typical desktop SXGA monitor has 1280 pixels horizontally and 1024 vertically - 1,310,720 pinpoints of light. The grid is fine enough to give human vision the illusion of a picture. The screen image is rewritten about 60 times per second (sometimes more) but the computer isn't concerned with that, the graphics adapter does it from it's own local memory. To put something looking like a typewritten page on the screen the application calls the graphics library and is allocated a window. The application then tells the graphics library what it is going to display and that gets laid out in the graphics adapter memory. If that window is the one on top the graphics adapters raster scan process repetitively copies the bitmap in memory onto the screen creating what looks like a solid image.

    If the user does something, pressing a key or moving the mouse then if the mouse-pointer is over that window the application is notified of an event. For instance moving the scroll bar creates an event that requires the application to send more information. Creating the appearance of documents on a screen needs substantial amounts of computer power. If the computer is busy the screen might not refresh quite as it should and the illusion of a piece of paper breaks down leaving blank screen for a moment.

    If the user presses print (or drags the file onto the printer) then the application calls system print routines. There are usually similarities between screen and print and there have been attempts to have a single graphics language such as Display PostScript.   However there are differences as well.

    • The screen shows a limited view of information with scroll bars. The printer is usually expected to produce the whole document, regardless of length.
    • Screens are closely bound into the computer, or at least the graphics adapter is. The DirectX or OpenGL GDI   gives the computer close control over what the screen shows. Printers and computers have historically just shared a print language. The print subsystem may give very little feedback to the computer.
    • A notebook screen is typically about the size of A4 and a desktop the size of A3, but they are used landscape rather than portrait. Word processors do try to carry screen presentation over to the printed page. Web pages can use completely different style sheets.
    • Screens resolution is lower - under 100 dpi for many screens and over 300 dpi for almost all printers. People are less critical of the look of things on a screen than they are about a printed page.
    • Screens may need less resolution because they can handle continuous tones, often called greyscale. Any pixel on the screen can be set to just about any colour levelby contrast a colour printer can usually achieve just 8 colours and makes up for it by printing a mixture of tiny coloured dots which give the right overall look to the page.
    • Screens are usually based on a single graphics adapter that is the same age as the computer. There can be several printers and they may work in mixed environments. It is quite common to find a ten year old network printer working alongside recent computers, and to find a printer working with a network of Windows, Apple-Mac, Linux and Unix machines.   Computers and printers need a common language.

    Computer print-drivers turn material from whatever format the file in the computer specifies into a print language. Computers and printers have a complicated history so there isn't a single print-language, although HP PCL and Adobe PostScript come close.

    Print languages reflect the diverse way information is held in computers, the mixture of text, font specifications, vectors and bitmaps, often called raster images where printers are concerned.

    • Text was once limited because daisywheel and band printers had only one font.  There were scarcely any graphic abilities either. With simple text a print language is little more than sending traditional teleprinter character codes (ASCII).laser and inkjet printers commonly use fonts defined as vectors which can be scaled. In recent systems text is usually held as vectors.
    • Vectors are numeric coordinates.   Coordinates might specify an image at a given scale, but they can be multiplied or divided by any amount to give an image at another scale. An image that works on a screen can therefore work on any size of paper, from postcard to poster sized.
    • Designers historically tried to avoid raster images for several reasons.
    • They are difficult to scale. Take an image intended to be postcard sized and it looks grainy blown up to A4 and blocky extended to poster size.
    • They can be large; an A4 page at 300 dpi with no greyscale equates to just about a megabyte of data. Twenty years ago a megabyte was a lot of memory. (An A4 page at 1200 dpi with 32 bit colour specified is 64 megabytes, that still is quite a lot)
    • The computer application turns whatever data it holds into a form that the print subsystem can accept. For instance the CUPS print subsystem accepts Text, HP/GL, PDF, PostScript and raster images.
    • Filters convert these to one or two common forms; PostScript or Raster in CUPS for instance. Then the ps-to-raster filter might convert PostScript to raster. Raster (bitmap) images are the lowest common denominator of graphics - always reproducible but sometimes lacking efficiency. Alternatively the foomatic filter will convert from PostScript into one of the printer's native languages using directions from a ppd configuration file.
    • A further series of filters then forwards the print language, or wraps the pre-formed raster in the print language. The data is transferred over a local or network connection to the printer in a supported language, which might PCL, Epson ESC/P or PostScript.

    What the printer does depends on the language it is being sent and what kind of technology it uses. A cheap home inkjet printer that only supports the Lightweight Imaging Device Language (LIDIL or LDL) expects the computer to make up it's raster image for it. Almost all the effort of making up the page is done in the computer, not the printer. The users PC turns a page of A4 print at 300 dpi into megabyte of data, which is sent to the printer and scanned onto the page. If the computer slows down the printer will pause at the end of a line. If a PCL printer is sent raster images wrapped in PCL packets the result isn't much different.

    PostScript is a recurring theme.   Unix oriented systems (Apple, BSD, Linux, Solaris etc) are particularly likely to use PostScript all the way through the print process. The advantage of this is not just that a lot of the filter conversion stages are eliminated. Application, computer and printer all deal with the same graphics language so the probability of annoying errors should be reduced. The slight problem is that PostScript was designed to be a general purpose graphics language, so it can be more verbose than necessary in specifying a printed page. HP designed PCL for printers so it is more efficient at the task.

    People with a new Windows PC and an inkjet printer next to it have no reason to care that the computer uses its processor to make up a megabyte (A4 300 dpi) or even 126 megabytes (A4 1200 dpi colour) page image and feed it to the printer.

    Things look very different if a network of several people are doing the same or if the pages to print are made up on a server, then you might value the efficiency of the printer doing most of the work.

    Laser Printers

    Laser printers have to work at their rated speed if they work at all. Once the rollers start to turn they cannot stop until the page ends. The laser scanner rotates at high speed and the laser scans out a raster (aka bitmap). To ensure this the printer typically makes up and holds the image of the page in it's own memory before printing starts at all.

    Laser printers turn a photoconductive drum and scan a laser beam horizontally across it to create the image. Most have a single laser that must produce however many dots there are on the page - about 126 million for an A4 page at 1200 dpi. If the printer has greyscale abilities then each dot must get the right amount of energy so the laser needs to get the right analog value very rapidly.

    Laser printers sometimes think for a long time because they are trying to rasterise a complicated image in limited memory.

    A problem with old printers is that they won't always handle newer print jobs containing big bitmaps. Laser printers may slow down dramatically when the print job complexity exceeds their memory capacity. Older printers from the 1990s often had just a couple of megabytes of RAM; memory was an expensive commodity and printers weren't usually expected to print photos.

    Laser printers that seem unduly slow probably need more memory. An alternative is to change the print language (switching from PostScript to PCL can halve the memory footprint of a job) and / or reduce the resolution. Dropping resolution from 1200 dpi to 300 dpi drops the size of an A4 mono raster image from 16 megabytes back to 1 megabyte.

    Inkjet Printers

    Inkjet printers work very differently from laser printers, they only have to deal with one swath of the page. A swath is usually less than a tenth of what the laser printer needs to deal with. Inkjet printers don't need to hold a great deal of data before they start to print. When the printhead has passed over the page it can stop and wait for more data from the computer.

    The inkjet swath is made by a row of nozzles each of which contributes to the image. A thermal inkjet fires a nozzle by heating a small ink chamber to the point where some liquid vapourises and forces a droplet out. Heating a chamber takes time, so does the flow of fresh ink into an empty chamber. Nozzles work thousands of times per second but there is a limit to their cycle time.

    Thermal inkjet head manufacturers can put some number of nozzles in a head. Early printheads had 12 nozzles in a vertical line about 4mm high; this gave crude print quite slowly because printing a whole A4 page would need something like 70 passes of the head across the page.  Recent printheads have a thousand or more nozzles in a head about 25mm high; this gives very fine print and since the head might only need 10 passes across the page it can be much faster.

    Inkjet printers often have headline print speeds of 30 pages per minute but will only achieve that on really simple print jobs like a paragraph of correspondence in draft mode.

    Inkjet printers are notable for slowing down as the image quality goes up. The basic tradeoff is that printheads only have a limited number of nozzles - 12 on early models in the 1980s and hundreds or even thousands now. Each nozzle is capable of making several thousand dots per second. A densely printed image with strong dark tones will need a lot of dots.

    Inkjets have an additional reason to slow down for fine work. Printhead movement is normally driven be a motor through a rubber belt. The printer's processor knows where the printhead is because it gets feedback from a sensor. Printing fast there can be problems with the accuracy of dot positioning.

    Laser printers tend to have one speed - fast or stop. Inkjets tend to run at anything from one page per minute to 30 pages per minute. Producing a full colour photograph takes more than a minute on some inkjets.

    Most of what has been said about inkjet printers applies to machines that scan the printhead back and forth. But if printheads have about 10,000 nozzles or more arranged across an A4 page the printhead no longer has to move. All that moves is the paper and the droplets of ink.

    This is what HP's CM8050 and CM8060 Edgeline printers do, giving pages at 600x1200 dpi resolution and 60 page per minute speeds from an inkjet mechanism.

    Memjet printers developed by Silverbrook research use 70,000 nozzles to print a page per second. Memjet seems to be aiming at a much lower price point than the HP edgeline so if their technology proves reliable it will shake up the printer market.

    Dot Matrix

    Most dot matrix printers are like older inkjets, a similar scanning speed and just nine pins (the first inkjets had 12 nozzles to make them a bit better than dot matrix). Later versions of dot-matrix printers had more pins - there were 18, 24 and even 48 pin dot matrix printers. The problem with 48 pin heads proved to be that the pins were too fine and easily bent. With pins 0.1mm across or larger the dot matrix printer could not achieve resolutions better than 250 dpi and the print just looks too grainy.

    Dot matrix printers specialise in low cost multi-part print. If you need a forensically verifiable carbon copy then a dot-matrix is just about the only remaining solution.

    Dot matrix printers can be quite fast. One way to achieve that is to put several heads across the carriage, each dealing with part of the page. Printers with two heads used to be quite common. With four heads the mass of the carriage became a definite issue, the carriage motor has to accelerate the heads in each direction and a heavier carriage needs more energy, or moves slowly.

    Dot matrix printers might outpace laser printers or ordinary inkjets in some circumstances. Tasks like labelling often involve writing a short snippet of text on a relatively long piece of paper. With a laser printer the whole mechanism moves at one speed, in synchrony with the paper. A dot matrix printer can write the lines required and then increase the paper slew rate so that the next print position is under the printhead in less than a second.

    Shuttle printers or Line Matrix provides and answer to that problem. A row of print-pins spans the carriage, all printing at the same time. Dot matrix printers were expected to handle wide tractor feed paper and a 13.8 inch carriage would imply something like 3450 solenoids and pins. That isn't practical, so fast printers have something like a tenth or twentieth that many arranged in one or more rows. The whole row shuttles back and forth across a few millimetres of the page, so each pin deals with a character position. Faster printers have more pins and shorter throws for the shuttle. The Printronix P7000 achieves print speeds of 2,000 lines per minute which, combined with fast paper slew rate, may be higher than many industrial laser printers..

    Thermal Printers

    Thermal printers use a localised heat source to create a pattern on thermochromic paper. The heat sources can be small, less than 0.1mm across so resolution can be better than 250 dots per inch. They can also operate surprisingly quickly, with over 2,000 thermal cycles in a second. This type of printer is very widely used for shop till rolls, ATMs and labelling because it is fast and reliable. It used to be common in fax machines, but people don't like the shiny paper.

    The reason the paper looks odd is that it typically has a layer of dye material in its white form (a leuco dye) and a mild acid mixed in a thin coating of waxy material. When the wax is heated the acid mixes with the dye, which reacts and turns to it's coloured form. The change is permanent but one of the issues is that the paper yellows and fades more than plain paper. The other issue is that coating the whole paper surfaces has a cost, so thermal printing costs more than impact dot-matrix or inkjet.

    Printheads are thin-film resistors, usually an entire row of them embedded with a driver and control chip in a bar of ceramic. Printheads look rather unspectacular, there is nothing to see but the white bar of ceramic material with just some silvery marks where the elements are. Although the bar is being heated its just the surface in contact with the paper that gets momentarily hot and that is almost immediately dissipated into the structure of the bar and into the paper. Paper coming out of the device is not noticeably warm and thermal print is actually one of the lowest energy users amongst print technologies. there are very few moving parts, in many printers just a platen roller feeding the paper under the printhead.

    Thermal printers can be quite fast, some of the larger printers can produce 10 inches of material per second which is roughly equivalent to a fast office laser printer. Most thermal printers only have a platen 4 inches wide because they would never be used for ordinary office work, just for labelling and sales tickets.

    The selling points for thermal print are it's simplicity and reliability. The paper roll just drops into place and is threaded through the slot between the head and the platen roller. There is only one significant point of failure which is the printhead.

    Design Limitations

    Print speed reflects various mechanical limitations of specific designs. Laser printers would be one of the fastest processes but the fuser heating time gets in the way. Even instant-on isn't fast enough for a till roll.

    There are also software issues. Older printers tend to work more slowly because designing them to be fast would have needed a processor that wasn't cost effective. It was possible to make a faster printer but the processor to work it was expensive. Printer makers couldn't pack a gigahertz speed processor and a gigabit of memory (supercomputer stuff just ten years ago) into a printer.

    There are still processor limitations, but digital TVs and smartphones pack that sort of computing punch these days so it is affordable in a printer. But there are still the mechanical limits, a faster printer still needs the bigger motor, driver chips and power supply to drive the mechanism. And there is still the issue of feeding paper reliably. And there is a question about whether there is much demand for faster printers.

    Print speed can be a critical figure in certain situations. The till roll at the supermarket checkout has to complete printing before the checkout operator hands over the change, which is why they use fast, reliable thermal printers. perhaps because it often reflects other things like build quality. In most home and office use doubling the print speed won't double productivity, users just need to get used to setting print jobs away and then getting on with something else.

    In an office situation speed might be more critical. A call center handling insurance quotes might have a procedure at the end of the call where the operator prints what was on the screen and puts the documents into the envelope. If the printer is too slow the call-rate drops.

    Copyright G Huskinson & MindMachine Associates Ltd 2012