It seems that every time I think it’s safe to ditch content from my CompTIA A+ classes, CompTIA resurrects a zinger. One of my students recently (on the 801 exam) got a question on parallel ports, or more specifically, on LPT1. Here’s the scoop on these long-dead ports.
Early PCs offered only one built-in port, a round DIN connector for a keyboard. All other expansion devices (mouse, printer, joystick, speakers, etc.) plugged into ports of various types installed via expansion cards. The two most common ports were serial ports and parallel ports.
We used serial ports for mice and modems, primarily, and parallel ports for just about everything else. Both types of ports required assignment of specific system resources that were standardized throughout the IBM PC universe and thus got names associated with them.
It was assumed that each PC would have up to two serial and two parallel ports that would get assigned resources as COM1 and COM2, and LPT1 and LPT2, respectively. Most technicians and users called the serial ports and parallel ports by their resource names, so “serial port 1” was “COM1,” for example.
Both serial ports and parallel ports have gone away from modern PCs, but a few old devices that need them refuse to die. My office still has an HP LaserJet 4, for example, that was made before printer companies realized the money was in toner and ink. It just keeps working. And it connects to a parallel port.
If you find yourself with a legacy device that needs a parallel port, you can find a few expansion cards at my favorite store, Newegg.com. Chances are you’ll assign LPT1 resources for the port. (Just in case you get asked about such things on a CompTIA exam in your near future.)
Technical details:
• Parallel port = 25 pin female D-sub
• LPT1 = I/O address 378 and IRQ 7
• 8-bit