In the previous post we have discussed about Computer Input Devices, now let us have a look at different types of Printers which are Computer Output Devices.
TYPES OF PRINTERS
Printers are of two types;
1 . Impact printers
2 . Non-impact printers.
In impact printers a hammer strikes a carbon coated ribbon to print and it is easy to obtain multiple copies by placing carbon sheets between the papers. Whereas in non-impact printers it traces the characters to be printed using ink (or) graphite particles. It does not use hammers. All the different types of printers fall into either impact printers or non-impact printers.
Now let us discuss different types of printers in detail.
A drum printer consists of a cylindrical drum in which the characters [alphabets] are embedded on the surface of the drum. One complete set of characters is embossed for each print position on a line. Therefore a printer with 132 characters per line and a 96 character set will have on its surface that is 132*96=12672 characters embossed. The working mechanism is that the codes of all characters to be printed on one line are transmitted from the memory of the computer to a storage unit in the printer. A printer buffer register can normally store 132 character codes. The printer drum will be rotated in a circular motion at a high speed. A character is printed by striking a hammer against the embedded [embossed] character on the surface of the drum. As the drum rotates, the hammer waits until the character to be printed appears in front of it. Therefore the drum would have to complete on full revolution for a line to be printed. The hammer must strike quickly and it must be synchronized along with the drum movement. Otherwise the printing will not be uniform. The drum printers have a fixed font and cannot be changed often.
A chain printer has a steel band. This steel band is embossed with a set of characters on it. For printing a line, all the characters in the line are sent from the memory to the printer buffer register. For a 64 set printer, 4 sets of 64 characters each would be embossed on the band. As the band rotates, the hammer is activated when the desired character as specified in the buffer register comes in front of it. For a printer which prints 132 characters per line, 132 hammers will be positioned to strike the carbon ribbon which is placed between the chain and the paper. In chain printers there must be a healthy synchronization between the hammer movement and the chain movement. The font size of the character set can be changed in the chain printers as there are different chains with different scripts. The chains can be changed in chain printer.
A line printer prints entire line at a time. It generally produces only upper case alphabets [capital letters]. In rare cases in some line printers there is a provision of printing both upper case and lower case characters. In a line printer the printing speed varies from 300 lines to 3000 lines per minute with 96 to 160 characters or a 15 inch line. 6 to 8 lines are printed per vertical inch. To print large volumes of reports generally line printers are used. The quality of printing in terms of style and density may be poor when compared to other printers. This type of printer belongs to an impact printer.
DOT MATRIX PRINTER:
A dot matrix printer is a famous serial printer. In a dot matrix printer a character is made up of a finite number of dots. The appearance of the character may not be clear. This printer consists of an array of pins. The resolution of this printer is 9*7 or 7*5 array of pins. When we wish to print the character, that specific character is sent one character at a time from the memory to the printer. The character code is decoded by the printer electronics and activates the appropriate pins in the print head. These pins move forward to form a character and then they hit the carbon ribbon in front of the paper and the desired character will be printed on the paper. Most of the dot matrix printers are bi-directional. This provision increases the speed of the printing. It can print approximately 300 characters per second. In a dot matrix printer we can convert the alphabets in to different script like Tamil, Devanagari script etc. In this printer also multiple copies can be printed by placing carbon sheet between the papers.
In an inkjet printer characters are represented by sharp continuous lines called character printer. An inkjet printer consists of print head with a number of small holes. Individual holes are heated very rapidly by an integrated circuit resistor. Now, when the resistor heats up the ink near it vapourizes and this will be ejected through the hole and makes a dot on paper placed near the head. It can print 300 dots per inch. Latest inkjet printers have multiple heads, one per colour which allows colour printing. The speed is about 120 characters per second. Inkjet printers can also draw pictures and graphs along with printing.
In a laser printer an electronically controlled laser beam traces out the required character to be printed on a photoconductive drum. Now, the drum attracts an ink toner on the exposed area. This image is transferred to the paper which comes in contact with the drum. Now the desired character is printed on the paper. Very fast printers can print 10,000 lines per minute. Low speed laser printer prints 4 to 16 pages per minute. Laser printer gives an excellent graphic quality output. They can print variety of font styles, sizes etc. these printers are expensive.