Baud rate vs. bit rate - is there really any difference, in serial data transfer, if no modem is involved?

Question

I am confused. I know that, technically speaking, there is a difference between baud rate and bit rate. I know that baud rate is how many times a communication signal changes per second, and that bit rate is how many bits are transferred per second. I realize that baud rate & bit rate are not at all the same when a computer is communicating with a modem - although I can't say I know the details of why that is so (and would love if someone could explain that to me).

But it seems to me that in some contexts, baud rate and bit rate could be synonymous. Please tell me if there is any difference in this particular case. Say you have one computer transmitting binary data serially to another computer through a cable that is plugged into a serial port at both ends. The program that is transmitting data can be configured to transmit the serial data at any standard rate, between 1200 bps and 921600 bps in exchanging data. So even if the receiving computer was not capable of the same bps rate as the sending computer (i don't know enough to know if that is even a possibility), the sending computer's rate could be adjusted to match that of the receiving computer. I don't see how, in that setting, there is any difference between 19200 bits transmitted per second, and 19200 signal changes per second, since the only possible signals are 0 and 1. So to me, it seems like in this context, if you are using the same numeric figures (such as 19200) for both baud rate and bit rate, they are synonymous. So my first question is - is it true that, in the context I just described, baud rate and bit rate are functionally equivalent?

Also, I've heard that sometimes slightly more or less than a single bit may be transferred at a time. This leads to my second question: does that really happen? If so, what equipment would be involved? under what circumstances would it happen, and why?

Answer 1

Yes. In this context baud rate and bit rate are the same. Baud rate, as you rightly described, is simply the number of symbols per second; a symbol may have 2 or more bits represented by it. Since there is only a serial connection between the two systems, and there is no modulation involved, baud rate is the same as bit rate. You have that part absolutely correct.

The second issue you mention is about bit rate. In serial communication, only one bit at a time can be transferred down a single channel. Perhaps the bit-rate being less than 1 had something to do with the stochastic probability of corruption by noise, in which case you'd technically lose some bits to noise and get corrupted information. Since the complete bit sequence arrives at the receiver with an error, the effective number of bits transferred would be lowered. However, if you were to send multiple bits at a time, you'd simply use multiple serial ports i.e. a parallel port. You may use a "universal asynchronous receiver transmitter" to accomplish serial-parallel and parallel-serial conversions.

Hope I answered to your satisfaction. I might not have read your question well.

Answer 2

Baud Rate Vs Bit Rate

Answer 3

Baud Vs Bps

Answer 4

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RE:

Baud rate vs. bit rate - is there really any difference, in serial data transfer, if no modem is involved?

I am confused. I know that, technically speaking, there is a difference between baud rate and bit rate. I know that baud rate is how many times a communication signal changes per second, and that bit rate is how many bits are transferred per second. I realize that baud rate & bit rate are not at...