is capable of printing. If the printer is an 80-column
printer, the drum has 80 characters on each line.
The character drum is rotated at a high speed. As
the desired character faces the paper, a print hammer
for that column is activated or fired, forcing the paper
and inked ribbon against the drum. The character on
the drum is imprinted on the paper as shown in figure
12-6.
Normally, the hammer bank contains one hammer
for each character column of a line. If the printer has a
capacity to print 132 columns, then the hammer bank
will consist of 132 hammers. As a line is printed, each
hammer is fired as the character to be printed in its
column faces the paper.
A drum printer prints one line of data for each
rotation of the drum. Drum printers can print from 300
to 1,200 lines per minute, depending of the rotational
speed of the drum and how fast the printer can setup to
print the next line.
Chain and Band Printers
Chain printers use a print chain as a source of
raised characters. The links of the chain are engraved
character-printing slugs. The chain is made up of
several sections; each section contains one complete
character set.
The print chain is rotated at a high rate of speed past
the print positions (columns). As the desired character
faces the paper, the print hammer for that column is
fired, printing the character on the paper.
Band printers work on the same principle as chain
printers except that a scalloped, steel print band is used
instead of a print chain. Figure 12-7 illustrates part of
the band printer’s print mechanism.
To change the font (typeface) on a chain or band
printer, you change the print chain or band. Character
sets of the chain and band printers vary, but are typically
48 to 64 characters. Since hammers are of a freed size,
Figure 12-6.—Drum, ribbon, and paper relationship during printer operations.
12-8
