Exact value of the nominal 27MHz crystal

Zheng Zhao said:

For the typical 27MHz external reference clock, is 27M only a nominal value? What is its exact numerical value and error margin?

27M is the exact value to use. This and its error margin should be specified in datasheet. Why is this a concern for your design?

Zheng Zhao said:

And for various types types of oscillators, for example, the 32.768-KHz external reference clock for ARM1x's Real-time clock module, does that "K" equal to decimal 1000 or 1024 (2^10)?

I am not an expert on world-wide standards, but I have not seen a fractional number used in a 2^10- based suffix, and I have not noticed a 2^10- based suffix being used with frequencies. I have only noticed it with memory sizes. In this case, how could one interpret the fractional component of .768 into a 2^10- based number? Context should be the clearest method to determine 10^3 vs. 2^10 basis, would you not agree?