Arduino vs PIC nop. Is this the same thing?
A NOP usually takes 1 instruction cycle. The PIC12F675 seems to divide the clock by four for an instruction cycle:  


  "One instruction cycle consists of four oscillator periods;
  for an oscillator frequency of 4 MHz, this gives a normal
  instruction execution time of 1 \$\mu\$s." (datasheet p. 71)


So a 20MHz clock will give you delay of 200 ns (4/20 MHz).



The AVR used in Arduino OTOH delivers 1 MIPS/MHz, so at 20 MHz clock it will most likely give a 50 ns delay (1/20 MHz).