As I understand it, in the early days of personal computers, strict FCC limits on RF emissions, were a factor limiting the speed at which data could be transmitted over wires, but I'm trying to understand exactly how that worked. In particular, I came across the following surprising comment at http://atariage.com/forums/topic/239749-improving-800xl-sio-transfer-rate/
"The 400 and 800 were designed before the relaxed FCC rules, so SIO was bandwidth limited to work with 19.2 peripherals."
This referring to the SIO bus used to connect disk drives among other things to the Atari 8-bit computers, and 19.2 being in kilobits per second.
That is actually a very severe restriction, less than 3 kilobytes per second, much slower than the maximum transfer rate of a 5.25" floppy disk itself.
But the Apple II accessed disks at 15 kilobytes per second. How was this possible without running into the same limit?
Also, the Atari 800 was released in 1979. As I understand it, the new FCC rules came into effect in 1980, and were more restrictive rather than more relaxed (at least for class B, devices marketed for use at home, which would certainly include everything Atari sold); famously, the original TRS-80 generated so much RF interference that you could make up for its lack of sound hardware by putting it next to a radio and writing an appropriately crafted loop to generate the right pattern of interference to play music on the radio, but that model had to be discontinued at the end of 1980 for that reason.
So what were the actual limits on data transmission speed before and after 1980? And why exactly was Atari limited to 19.2 kbits/sec?