The first character printers were daisywheel printers and
were very slow. The bottleneck was created by the speed
at which the print head rotates a pin, placing the correct
letter in front of the hammer and then firing the hammer.
An effective method of measuring this speed was characters
per second (cps). It took time to move the print head over
to the next character position and to rotate the paper.
But, these events required little time compared to the time
spent to print a character. Early daisywheel printers printed
at about as fast as the fastest typists 10 characters per
second (10 cps). This meant that it took eight seconds to
print a line or about seven minutes for a page. A vast majority
of the time was spent actually printing characters. A small
minority of the time was spent moving the head and paper.
The fastest daisywheel printers reached speeds of more
than 55 cps, but these were specialized, expensive daisywheel
printers. The most cost-effective speed for daisywheel printers
was around 30 cps before those printers became extinct.
Dot-matrix printers always have been able to print much
faster than daisywheels, and they are much cheaper. Because
of this, daisywheel printers competed with dot-matrix printers.
Today, dot-matrix printers that print at 240 cps are not
unusual, and speeds of up to 800 cps are possible.
Back in the days of daisywheel printers, characters per
second was a good measure of a printer's speed. This was
because the daisywheel was the bottleneck. Today, it is
inappropriate to rate a printer's speed in characters per
second. Printer speeds are so fast that the time to get
to the beginning of the next line, advance the paper, dry
the paper, or melt toner is significant. Today, most dot-matrix
printers can print the line at 240 cps. This means it takes
one third of a second to print a line of 80 characters.
The time spent moving the print head into position for the
next line and advancing the paper suddenly becomes significant.
The slower the printer, the more accurate the cps value
is going to be. Average throughput of a printer rated at
200 cps is really only 100 cps once the movement of the
print head and paper is taken into account. Character-mode
speed is like the miles-pergallon rating of a new car; the
printer never seems to perform at the rated speed.
Laser printers operating in character mode could be advertised
as having a speed of millions of characters per second.
Because everyone would know this was a ridiculous speed
rating, laser printers are often rated in pages per second.
In character mode, the speed at which the printer can push
paper through is the bottleneck. To translate pages per
minute to characters per second, an assumption has to be
made concerning the average number of characters per page.
If a page has 55 lines and an average of 60 characters per
line, then each page has 3,300 characters. Usually, the
more accurate average is around 2,000 characters per page
because some lines are skipped, lines are not usually 60
characters long, and so on. If 2,000 characters are assumed
to be on the average page, here is the math:
8 pages 2,000 characters 1 minute
x x = 267 cps
minute page 60 seconds
8 pages 3,300 characters 1 minute
x x = 440 cps
minute page 60 seconds
Although inkjet printers are fast, you need to let the
paper dry for about three seconds before you stack it. This
reduces throughput to between 40 cps to 60 cps. Still, this
is fast, considering the letter-quality speed of most dot-matrix
printers. Most inkjet and dot-matrix printers print at between
one to three pages per minute.
The speed of printers attached to mainframes and minicomputers
is measured in lines per minute. When people move a massive
database off a main-frame or minicomputer to a PC, often
they must print the entire inventory or accounting journal.
Obviously, they would need a fast printer for this task.
Usually, these printers are printing 132 characters per
line; the math converting to effective characters per second
throughput follows:
500 lines 132 characters 1 minute
x x = 1,100 cps
minutes lines 60 seconds
100 lines 132 characters 1 minute
x x = 220 cps
minutes lines 60 seconds
Dot-matrix printers that are achieving speeds of more than
400 cps effective throughput are available (best is 800
cps). These speeds are obtained by using 18-pin print heads.
The 18 pins are divided into two groups of nine. These two
groups alternate; one group cools off while the other is
working.
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