I'm having a little trouble understanding the difference between an internal oscillator and clock speed of microcontrollers. I was under the impression the the internal oscillator oscillates at a certain frequency which IS the clock speed but I get the feeling that I'm wrong. I've seen the PIC16F690 datasheet that says that the oscillator can run up to 8MHz but the clock speed is 20MHz. Or is that 20MHz a maximum if an external clock is used?