36 Years and 1800 Issues of TidBITS

@Shamino David C.
Tue, 05 May 2026 19:39:01 +0000

Michael Schmitt:

… Compared to RS-232 on PCs that maxed out at 92 kbps.*

…

That’s straight from the interview: “Rather than putting in serial ports that operate at 9600 or 92,000 bits per second […]”, but I bet that was a transcription error in the original interview. 19.2 kbps would make more sense.

I agree that he probably said 19,200 (pronounced “nineteen point two thousand”, which might have been mistakenly transcribed as “92,000”.

That having been said…

PC serial ports could always go up to 115,200 bps, but the 8250 UART typically used at the time only has a 1 byte buffer, so at high bit-rates (anything above 9600), software often couldn’t keep up, causing characters to get dropped.

Enthusiasts would replace their 8250 chips with 16550A chips, which have a 16 byte buffer (and the later 16550AFN, which supports DMA), allowing reliable behavior at high bit-rates.

These faster UARTs became critical when dial-up modems got faster than 9600 bps (e.g., 14400, 28K and 56K).

Still, the Mac’s RS-422 capability had that beat out of the box, and its other capabilities made LocalTalk a practical reality, requiring only cheap transceivers, not expensive network interface cards.