Page 69 - DCAP101_BASIC_COMPUTER_SKILLS

Basic Computer Skills

Notes
Figure 4.19: Drum Printer

Ribbon
Signal synchronized hammer
Paper

Print cylinder

The drum rotates at a high speed. A character is printed at a desired print position by
activating the appropriate hammer when the character embossed on the band at the print
position passes below it. Hence, the drum would have to complete one full revolution to
print each line of output. This means that not all characters on a line are printed at exactly
the same time, but the time required to print an entire line is so fast that it appears as if
one line is printed at a time.
The drum of a drum printer is expensive and cannot be changed often. Hence, drum printers
can print a pre-defined set of characters only in a pre-defined style embossed on the drum.
Drum printers, therefore, do not have ability to print any shape of characters, different sizes
of print, and graphics such as charts and graphs.

Drum printers are impact printers because they print by hammering on a paper and inked
ribbon against the -3cters embossed on the drum. Hence, they can be used to produce
multiple copies by using carbon paper or its equivalent. Due to impact printing, drum
printers are noisy in operation and often use a cover to reduce the noise level. Printing
speeds of drum printers are in the range of 300 to 2000 lines per minute.

Chain/Band Printers
Chain/band printers are line printers that print one line at a time. Figure 4.20 shows the
print mechanism of a chain/band printer. It consists of a metallic chain/band on which
all characters of the character set supported by the printer are embossed. A standard
character set may have 48, 64, or 96 characters. In order to enhance printing, peed, the
characters in the character set are embossed several times on the chain/band. For example,
the chain/band of a 64 character set printer may have four sets of 64 characters each
embossed on it. In this case, the chain/band will have altogether 256 (64 x 4) characters
embossed on it. The printer has a set of hammers mounted in front of the chain/band in
a manner that an inked ribbon and paper placed between the hammers and chain/band.
The total number of hammers is equal to the total number of print positions. Therefore,
a printer supporting 132 print positions will have 132 hammers. The chain/band rotates
at a high speed. A character is printed at a desired print position by activating the
appropriate hammer when the character embossed on the chain/band passes below it.
Since the character set is repeated several times on the chain/band, it is not necessary to
wait for the chain/band to make a complete revolution to position the desired character
in the correct print position.
Unlike the drum of a drum printer, the chain/band of a chain/band printer can be changed
easily. This allows use of different fonts (styles of characters) and different scripts (languages)
to be used with the same printer. Like drum printers, chain/band printers can print only
pre-defined sets of charaLters embossed on the chain/band used with the printer. Chain/

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