Information and Communication Technology

2.1.32 Impact Printers 

Line printer

It prints an entire line at a time and is the fastest printer. Its speed varies from 300 to 3,000 lines per minute. It has been used in data processing applications for many years. Line printers normally have 132 print positions per line. This printer generally produces only upper case (capital) letters, though some have provision for both upper and lower case letters. The quality of printing in terms of style and density is poor for office use. However, they are used for producin g large volume of reports in big organisations.

Dot matrix printer

It is another impact printer which prints one character at a time. The print head comprises a matrix of tiny needles, usually of seven rows and five columns. They are electrically driven and punch characters in the form of patterns of tiny dots as shown in Fig. 2.8. The pattern of dots for each character is dictated by the information held electronically in the printer. Dot matrix printers can produce upper as well as lower case letters. Some printers are capable of producing compressed or expanded letters. Their speed varies in the range from 40 to 600 characters per second. The printing is poor for business reports. Nevertheless, they are used extensively on small computers because of their low cost. Matrix printers are much cheaper than line printers.

Daisy wheel printer

It is a character printer and derives its name from the shape of the print wheel. The daisy shape wheel is made of metal or plastic and holds the characters on its petals. The wheel rotates at a high speed and when the required character is positioned over the ribbon, a tinny hammer strikes it against the ribbon thus transferring the character symbol to the paper. Daisy wheels are interchangeable and therefore letters of different sizes and shapes can be used. These are slow printers, the ir speed ranging from 17 to 200 characters per second. But they produce good quality printing and are often used in word processing applications.