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Because if you had modems between the computers, you used straight-through RS232 cables -- the PC would have its Tx/Rx pins according to DTE standard, and the m
by myself248 16d ago
Because if you had modems between the computers, you used straight-through RS232 cables -- the PC would have its Tx/Rx pins according to DTE standard, and the modem would have its Tx/Rx pins according to DCE standard. The modems did the "swap" themselves by choosing tones at dial/answer/negotiate time, then the other modem-to-terminal link was likewise straight-through.
But if you were connecting two terminals directly with no modems, thus the modem was "null", you needed the cable to do the signal swap instead. Hence the name!
- wildzzz 15d agoI realized this the other day: it's funny that back in those days, you didn't have two computers (or teletypes) close enough together for them to talk to one another just through serial data. Why would two teletypes need to be in the same room? Just use a typewriter! And furthermore, how could you possibly fit two computers in the same room?! You probably had a phone line (or a radio set) handy so two modems would sit between the two devices and handle the long distance portion of the conversation. The null modem cable kinda developed as a thing once it actually made sense to have two computers in the same room that needed to share data faster than you could just enter it yourself.