14. What Speed Should I Use with My Modem?
By "speed" we really mean the "data flow rate" but almost everybody incorrectly calls it speed. For all modern modems you have no choice of the speed that the modem uses on the telephone line since it will automatically choose the highest possible speed that is feasible under the circumstances. If one modem is slower than the other, then the faster modem will operate at the slower modem's speed. On a noisy line, the speed will drop still lower.
While the above speeds are selected automatically by the modems you do have a choice as to what speed will be used between your modem and your computer (PC-to-modem speed). This is sometimes called "DTE speed" where "DTE" stands for Data Terminal Equipment (Your computer is a DTE.) You need to set this speed high enough so this part of the signal path will not be a bottleneck. The setting for the DTE speed is the maximum speed of this link. Most of the time it will likely actually operate at lower speeds.
For an external modem, DTE speed is the speed (in bits/sec) of the flow over the cable between you modem and PC. For an internal modem, it's the same idea since the modem also emulates a serial port. It may seem ridiculous having a speed limit on communication between a computer and a modem card that is directly connected inside the computer to a much higher speed bus. But it's usually that way since the modem card probably includes a dedicated serial port which does have speed limits (and settable speeds). However, some software modems have no such speed limits.
* License
