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A printer is a device used to produce a physical copy of computer data on paper or sheets of transparent cellulose called transparencies. Not all printers are the same. Printers are classified into different types based on the method used to produce printouts (printouts are also called hard copies).

Daisy-wheel

Daisy wheel printers were the first printers invented for use with computers. The daisy-wheel printer was an adaptation of the electric typewriters in use at that time. A daisy-wheel gets its name from the fact that it is round and wheel shaped and appears to have flower petals. Each of the petals on the daisy-wheel had a raised letter, number or punctuation mark. When printing, the daisy-wheel would rotate the correct petal into position and then push it against the printer ribbon and against the paper, just like a typewriter does. In this way, it transferred a character to the paper. If you wanted to print a different style of characters on a daisy wheel printer, you have to change the wheel.

Drum

A drum printer used a horizontal cylinder called a drum that had raised characters on it. The paper was thrust forward to meet the drum at the location where the desired character is located.

Laser

A laser printer uses light generated by a laser and reflected by a moving mirror. The mirror is used to direct the laser beam so that it draws whatever is to be printed. If you are in a place where your grocery store has bar code readers at the checkout, you will notice (if you dare to look inside) that there is a round spinning object covered in tiny mirrors. This same type of spinning mirror is inside the laser printer. The laser beam is reflected off the rotating mirror and strikes a special horizontal cylinder within the printer called a drum. Wherever the light hits the drum, it generates a static electric charge. Static electricity has an interesting property: it attracts small dust particles quite easilly and holds them as long as the static charge lasts. As the drum rotates, the charged portions of the surface of the drum pass a supply of special powder called toner. The toner is given a charge opposite of the drum (static charges can be either positive or negative) drawn to the statically charged surface of the drum where it sticks until the drum comes into contact with a sheet of paper. The paper fed into the printer then passes under the drum where the static is discharged and the toner is deposited onto the paper. Next, the paper passes over a heated roller called a fuser. The fuser heats the paper and the toner causing the toner dust to fuse together and to fuse to the paper. Until recently, laser printers could only print in black but recent technological advances have made color laser printing not only possible but quite affordable. While laser printers are usually the most expensive, they tend to last the longest, print the fastest and can print the highest number of pages.

Ink Jet

Ink jet printers are much simpler than laser printers. They spray ink, onto a piece of paper. The jets that spray the ink are often too small to be seen by the naked eye. Some ink jet printers use a thermal transfer process--the ink is squirted out and the heat transfers the ink to the paper.

Dot Matrix

Dot matrix printers use a head that contains rows of pins. These rows are called a matrix. A ribbon sits in front of the print head and the pins are pushed forward until they push the ribbon into contact with the paper, thereby transferring ink from the ribbon to the page. Dot matrix printers were some of the earliest printers and were developed after impact and daisy-wheel printers to solve the problem of drawing images on paper.

Printing Terminology

Resolution

This is generally synonymous with dot pitch. Resolution refers to the number of dots a printing device can produce on paper. In the case of printers which do not produce dots, but print whole characters (impact printers, daisy-wheel printers etc.), there is a characters per inch rating.

Dot Pitch

Dot Pitch refers to how many dots the printer can generate in one inch either horizontally or vertically across the page.

Pages Per Minute

This is the number of pages the printer can produce in one minute. If the printer has more than one printing mode (different resolutions, color vs. black and white) there may be more than one speed listed. The fastest speed for a color printer is always draft mode in black and white.

Fonts

Computers print text. To dress up the text, different fonts exist. Fonts are just different, fancy and pretty ways of printing the same set of lsetters and numbers. Fonts come in different styles and each font has a name. Fonts can have serifs--they have little bars at the ends of the letters like this capital 'i': I. Fonts can be drawn without serifs (called sans-serif which means 'has no serifs'). Fonts are also either fixed width or variable width. Fixed width fonts line up into nice columns on paper because every letter is trawn using the same ammount of space on the page. Variable width fonts use a different amount of space for each letter based on the shape of the letter. For example, a fixed width font uses the same amount of space for the letter 'w' as for the letter 'i'. A variable width font uses a different amount of horizontal space for the letter 'w' as it does for the letter 'i'.

Resident Fonts

Most printers have one or more built-in fonts--fonts that are already stored in the printer when you buy it. These built-in fonts are referred to as resident fonts.