The parallel port

I wrote a popular post about serial ports once, and serial ports are something I think about, worry about, and dream about with some regularity. Yet I have never really devoted that much attention to the serial port’s awkward sibling, always assuming that it was a fundamentally similar design employing either 8 data pins each way or 8 bidirectional data pins. It turns out that the truth is a lot more complicated. And it all starts with printers. You see, I have written here before that parallel ports are popular with printers because they avoid the need to buffer bits to assemble bytes, allowing the printer to operate on entire characters at a time in a fashion similar to the electromechanical Baudot teleprinters that early computer printers were based on. This isn’t wrong, it’s actually more correct than I had realized—the computer parallel port as we know it today was in fact designed entirely for printers, at least if you take the most straightforward historical lineage.

Let’s start back at the beginning of the modern parallel port: the dot matrix printer.

The serial port still sees tons of use today, but the parallel port seems to have vanished entirely.


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