Printers
The printer is used to make a paper copy (called a "hard copy") of the documents that you create on the computer. To print, you need to attach and install a printer. Printers fall into two major classifications:
  • Impact Printers - An impact printer produces printouts much in a simular way as typewriters. Characters are formed by a hammer or pin striking a ribbon saturated with ink against the paper.

  • Non-Impact Printers - A non-impact printer does not require contact to the surface of the paper to produce a printed image or character. There are several methods used to print pages such as ink spray, laser heat, or photocopying . Since the non-impact printer has fewer moving parts, it is the fastest and quietest of printers available.

Inpact Printers
Most impact printers are Dot Matrix; however, there may still be a few Daisy Wheel printers left. 

  • Dot Matrix Printers - Work by striking small pins (also called print wires) against an inked ribbon placed between the paper and the print head. (much the same way as with a typewriter)

    Print resolution (quality of printed material) is determined by the number of pins used to form letters and numbers.

    As an example - A character on a dot matrix is represented by either 9 , 18, or 24 pins, with 24 pins being the common number today. Printheads with more than 9 pins have two rows of pins with each row offset slightly.

    Not all pins are used to display a character. A code is used for each character to control which of the pins strikes a ribbon that is pressed against the paper.

    The resulting dots form images or characters on the paper. The pins are arranged by rows and columns into a pattern called a matrix. The most commonly used are the 9-pin and 24-pin dot matrix printers.

    Dot Matrix printers are not as popular as other types of printers, but they are less expensive. Dot Matrix printers are normally when you have multi-layer forms. Dot matrix printers are an inexpensive means for printing draft copies of documents for editing.

  • Here is how they work

    • Inside the printhead there is a large permanent magnet. This magnet exerts a force on the pins drawing them close to the surface of the magnet.

    • A spring on the print wire tries to force the pin away from the magnet.

    • The print wire is wrapped with a coil of wire that makes it an electro-magnet.

    • When power is applied to the coil, the resulting opposing magnetic field nuturalizes the permanent magnets field and allows the spring to force the pin forward to strike the ribbon.

  • Daisy Wheel Printers - This type printer produces a printed page by using a print wheel. The name Daisy Wheel comes from the fact the print wheel resembles a daisy flower. A raised character is placed on the tip of each of the daisy wheels petals. To print, the wheel is spun until the desired character is in front of a hammer.

    The hammer then strikes the character against an inked ribbon, the ribbon hits the paper, and an imprint of the character is left on the paper. These printers are commonly referred to as " Letter Quality Printers" as the print quality is as good as that of a typewriter. These printers are usually very slow because of the time required to rotate the print wheel for each character desired.

Non-Inpact Printers

  • Laser Printers Without a doubt, the laser printer is the fastest and most popular printer on the market. Lasor printers do not print multiple copy forms.

    The average laser printer produces extremely high quality printed images, with some able to produce near photo quality images or graphics.. They are somewhat more expensive than a dot matrix printer, especially if you purchase a high volume, high quality laser printer.

    Here is how they work A laser printer uses the Electro- Photostatic process to form images on paper. Laser printers use a drum that is covered with an organic substance sensitive to light. Output data from the computer is written by flashing patterns of dots onto the rotating negatively charged drum.

    The image of the entire page is built on the drum by neutralizing the negitive charge of the drum wherever the laser beam strikes.

    Toner is then attracted to the neutral charged areas. As the paper moves under the drum the toner is transferrer to the paper.

    The toner is then heated or fused into the fibers of the paper producing the printer document. There are six specific steps to this process.

    • Step 1 - Cleaning The photostatic drum is scraped of any residual toner from the last printed page. The toner is physically scraped from the drum.

    • Step 2 - Conditioning - A solid wire know as the Corona wire is used to apply a uniform negative charge on the drum thereby erasing any electrical images.

    • Step 3 - Writing -Writing to the drum is accomplished by using a laser beam. When the laser beam (light) hits the surface of the light sensitive drum, the drum looses its ability to hold an electrical charge (Remember the drum has a uniform negative charge). an latent image (like a photo negative) is formed on the drum in a series of tiny dots.

    • Step 4 - Developing -Negatively charged toner (finely ground plastic) is attracted to the more positive charged latent image. This forms the image that will be written on the paper. The toner particles that are repelled from the drum create the non-printed areas of the page.

    • Step 5 - Transferring - The developed image is then transferred to the paper. The paper has a strong positive charge that attracts the negatively charged toner particles producing the image on the paper. This is done by passing the paper between the drum and the transfer roller.

      Step 6 - Fusing - To make the image permanent the is passed through the fuser assemble. The fuser assemble consists of the fuser roller and a pressure roller. The fuser roller is heated enough to melt the toner particles and the pressure roller presses them into the fiber of the paper.

  • Some of the advantages laser printers have over dot matrix printers are:

    • Print different styles of printing in the same document.

    • Print Scanned photos or high resolution graphics.

  • Inkjet Printers - literally spray words and graphics on a page in near silence. Moderately priced, the print quality rivals that of a laser printer. Inkjet printers produce images by spraying liquid ink onto the paper through a miniature nozzle similar to your garden hose nozzle.

    Here is how they work:

    • The print head contains 4 cartridges of ink (magenta, blue, yellow, and black).  Certain types of cartridges have as many as (50) ink filled chambers, each with a tinynozzle.

    • The print head moves along a bar from one side of the paper to the opposite side. It writes as it is spaced across the paper. The print head gets its information from the formatting information and data sent to it. It uses this information to activate the chambers of the ink cartridges.

    • Once the proper nozzles are selected to form a character or area on the paper, an electrical pulse flows through thin resistors in the chambers that will be used to form the character to be printed.

    • The resistor is heated and used to heat a thin layer of ink in each selected chamber. This causes the ink to boil or expand to form a bubble of vapor.

    • The expansion causes pressure on the ink, which pushes the ink through the nozzle onto the paper. A typical character may be 20 drops across and 20 drops high - wow - that means for a single character, you may have heated up to 400 chambers of ink and sprayed it onto the paper using pressure of the heated ink.

  • Color Thermal Printers- These are the most expensive types of printers. They are high quality. These use special coated paper that costs approximately $.25 per page.

    Here is how they Work

    • The paper is fed into the printer engine. The paper is held against a ribbon coated with colored ink (cyan, magenta, yellow, or black).

    • As the paper moves through the paper feeders, it presses against the cyan bank of the ribbon. One or more heating elements are turned on, and they melt small dots of the cyan dye. The melted dots are then pressed against the paper.

    • The paper continues to move through the paper feeders until the paper peels away from the ribbon. As it peels, the unmelted ink remains on the ribbon, and the melted dye sticks to the paper.

    • The paper is pulled back into the printer, and the next color (magenta) band goes through the same process. This repeated for the magenta, yellow, and black.

    • After all color cycles, the paper is ejected into the paper tray at the exit.

  • No matter what type of printer you use the printer cable goes from the printer to a printer port LPT1 (a DB25 female connector) on the back of the computer.

  • The printer port can be either a parallel port or a serial port.

  • With a serial connection (COM port) the data is sent one bit at a time

  • With a parallel connection (LPT port) the data is sent one byte (8 bits) at a time.

  • All color from printers is from a mixture of colors.

  • All colors are mixed as dots of different colors.

  • Each printed color is a mixture of 4 colors (black, magenta, yellow, and blue).

  • Color thermal printers are higher quality than laser or ink jet printers because the heated wax does not bleet into each other or soak into the special paper.