Every IBM PC keyboard made has a PrtSc key, which means
"print the screen." After you press the PrtSc
key, a copy of the 25 lines and 80 columns on-screen is
sent to the printer. This key works because the screen and
the printer are usually in character mode. The trouble is
that the IBM PC video-board has a unique character set developed
by IBM. When you display lines, boxes, or character graphics,
pressing Shift-PrtSc may print some other characters.
The PrtSc key on an IBM keyboard is an important management
and troubleshooting tool. When foreign letters are displayed
instead of the lines representing a box, the utility of
the PrtSc key is ques tionable. Don't purchase a printer
and attach it to the IBM PC unless it can display the IBM
character set. Sometimes, this character set is referred
to as the graphics character set, higher order ASCII, or
upper ASCII character set.
Before ink cartridges and laser printers listens to data arriving on cables from
PCs from two types of interfaces (Serial and Parallel) now
it has all been changed to the USB (Universal Interface).
Interfaces differ in speed, price, sharing capabilities,
availability, cabling hassles, and cable lengths. In this
web section, we will try to define and explore these interface
features in general and then reviews specific interfaces
(please note that the information here will not be complete
and 100% accurate, so we suggest for you to find other sources
with more detailed explanation ).
Interface speed does not become important until the printer
and the PC can work faster than data can be transmitted
over the cable. The printer or the PC has always been slower
than the interface; thus, the speed of an interface is not
nearly as important as the speed with which a printer can
image data or a PC can transmit pixel information in graphics
mode. Only in the case of a serial interface can the interface
slow down the PC and printer. In this particular case, serial
port speed is measured in bits per second (bps). Most modern
serial interfaces are set at 9,600 bps for laser printers
and 2,400 bps for dot-matrix printers. These speeds can
be translated into the characters per second (cps) at which
a printer would have to print to keep up with data coming
through the cable by dividing by 10. For example, 9,600
bps is equal to 960 cps, and 2,400 bps is equal to 240 cps.
At these speeds, the cable transmits data faster than the
printer can print characters. However, font downloading
is not limited by the printing activity of the printer.
Instead, font downloading is limited by how fast the printer
can receive information and transfer it into memory. This
occurs at speeds of more than 2,000,000 bps. The newer interfaces
(Video and SCSI ) can operate at these speeds. However,
these interfaces are not needed for normal, character-mode
printing. Serial, RS-232 interfaces are the lowest in cost.
A ranking of interfaces in terms of cost from lowest to
highest includes the RS-232, parallel, video, HPIB, IAN,
and SCSI. All the interfaces mentioned can share a cable
with multiple printers and computers attached.
Although the printers of the world can have many different
interfaces, most individual printers come with only one.
The matching interface for the PC is most often built into
the PC or Macintosh. If not, you must add a board. The most
widely available interfaces are the serial (Macintosh) and
parallel (PC).
The interface with the most cabling problems is definitely
RS-232-the cheapest interface. All the other interfaces
use standard cables that make them much easier to install
and maintain. These interfaces usually come in standard
fixed lengths 15 feet or less.
This web section tries to define what is normal in the PC and
Macintosh worlds. Hewlett-Packard is an important vendor
of printers. Just as Epson dominates the dot-matrix market,
HP dominates the laser (printers using laser toners) and
inkjet cartridge market (printers using inkjet cartridges). HP also sells
PCs, as does Epson. HP also has its own printer interface
called HPIB. Most HP printers come with standard parallel
and serial interfaces, since the release of the original
HP LaserJets.
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