Printers are on-line devices initially categorised as being either impact whereby a printing head assembly of some type is in physical contact with the paper, and non-impact where there is no mechanical contact with the paper.


Impact printers:

Dot matrix printers; employ a set of pins that can be projected or withdrawn as required to form a dot matrix of the required character that is fired through an inked ribbon to form characters on an underlying sheet of paper.

Advantages:
Software is often provided by way of firmware, a selection of fonts and text styles can be produced and they are reliable.

Disadvantages:
Dot matrix printer tend to be noisy; They create fuzzy, low-quality characters and are not suitable for light quality or light volume output.

Daisy wheel printers; employ a metal or plastic wheel with raised letter or character embedded into the end of thin strips extending from the centre. The wheel spins to position the correct character under a single hammer which strikes it, forcing the character through an inked ribbon onto the paper.

Advantages:
Software is often provided by way of firmware and they are suitable for light quality output. They create high quality characters and are suitable for high quality or light volume output

Disadvantages:
They tend to be noisy, slow and are not capable of producing graphics.

Barrel (or Drum) printers; employ a revolving barrel that contains a set of 32 characters, each of which has a hammer, which allows each print position to impact the correct letter for that position through an inked ribbon. This mechanism allows all the characters of the same type to be printed simultaneously.

The process is required for all the required characters to build line of text the drum rotates so that the next line can be printed.

Advantages:
They are suitable for high quality, high volume output (up to 2000 lines per minute).

Disadvantages:
They are only able to produce print in one font and style and are not capable of producing graphics.

Chain printers; employ a revolving chain that contains one of more sets of characters which revolves in front of 132 hammers, which allows each print position to impact a character through an inked ribbon as it passes the appropriate place on the line. This mechanism potentially allows a complete line to be printed in one pass.

Advantages:
They are suitable for high quality output and some chain printers are able to produce more than one font and/or style. It is capable of very high speed.

Disadvantages:
they are large free standing printers and are not capable of producing graphics.

Drum plotters; operate by moving a pen across the paper to create horizontally movement and the paper revolves around a drum past the pen to create vertical movement. This mechanism allow text of images to be drawn.

Advantages:
They are capable of producing high quality output and can use large paper (for example A3).

Disadvantages: v They are not suitable for high volume output.

Flatbed plotters; operate by moving pens mounted on a carriage that moves over a board. The carriage moves in 365 degrees over the paper placed on a board under the pen.

Advantages:
They are capable of producing high quality (colour) output and can use large paper (for example A3 or A1).

Disadvantages:
They are large free standing printers that are not suitable for high volume output.

Non-impact printer:

Laser printers; apply an electrostatic charge to a rotating drum inside the printer. A laser or a light-emitting diode then discharges portions of the drum according to a sequence of electronic signals representing images or text that is build line at a time. The drum rotates so that the next line can be created.

As the drum rotates, it makes contact with charged plastic like powdered ink (toner) attaches itself to these discharged sections. A piece of paper that is given a greater charge than the drum is passed over the drum, transferring the toner. The toner is heated and fused to the sheet.

Advantages:
They are capable of producing extremely high-quality text and graphics (including colour) at extraordinary speeds, are suitable for high volume output and the consumable costs are low.

Disadvantages:
They are more complex and considerably more expensive than most other common printer types, require more memory and power.

Ink jet printers; employ a set of nozzles embedded in the print head through which small ink droplets are sprayed onto the page in a matrix of ink dots to form images or text on the page.

Advantages:
They are capable of producing colour text and images with near-photographic quality.

Disadvantages:
They are prone to clogging and the consumable costs are considerably high.

Direct thermal printers; employ an array of heated rods embedded in the print head that selectively burn a matrix of dots on heat sensitise thermograph paper to form images or text.

Advantages:
The consumable costs are lower other prints as ink is not needed. They are capable of producing images as well as text.

Disadvantages:
They are not suitable for light quality or light volume output, and specially prepared papers is needed.

Thermal transfer printers; employ an array of horizontal heating elements, one for each print position that melts ink from a ribbon to form a matrix of dots which is transferred to the pater to form images or text.

Advantages:
They can print very attractive labels on a broad range of media and the consumable costs are lower than some other common printer types.

Disadvantages:
Requirement for specially treated paper. Affected by temperature changes.