Going Parallel and Serial: Disappearing Acts ...........................................
A long, long time ago — at least a couple of years in the ancient past — one of
the primary means of communication for desktops and laptops was the paral-
lel port. Today, though, parallel ports, old-fashioned serial ports, and floppy
disk drives are pieces missing from modern laptops. If you absolutely insist
on having one, you’ve got to add these as external devices.Listing to port .....................................................................................
So, what was a parallel port, and why has it gone missing?In early designs of computers, engineers found they could transfer data fast
and accurately by creating an eight-lane superhighway and spread an 8-bit
computer word so that it moves one bit alongside each other down this
parallel set of wires. This was deemed a better design than stacking up the
computer words so that one bit ran behind the other with the additional
overhead of codes to mark the beginning and end of each word.But as I explored in this chapter, new technologies have allowed engineers
to push bits through a two-wire serial connection at extremely fast rates.
Parallel communication paths have reached a point where speed is slowed by
tiny imperfections in the wires, resulting in parallel words no longer traveling
in perfect perpendicularity to each other. In other words, some of the bits
may drag behind the others, slowing down the entire highway.The original design for a PC parallel port was to send information in one
direction and for one purpose: from a computer to a printer. That may have
been why it was also called the printer port. Another name, LPT1,reaches all
the way back to mainframe printers, which used to be connected to a line
printer, a huge clanking machine that assembled a line’s worth of text on a
row of rotating wheels and then punch it against a ribbon. Line printers are
long gone, but deep within the settings of a modern computer you still see
references to a device called an LPT (as well as one called COMM, which is a
synonym for an old-style serial port).As computers and devices became more capable, the parallel port’s design
was modified slightly to allow movement of data and instructions in both
directions; enhanced or bidirectional parallel ports could receive an out-of-
paper or out-of-ink signal from a printer.Chapter 16: Breaking Out of the Box: PC Cards, USB, and FireWire 247