How fast is 1 MHz in an AVR microcontroller? Is it actually 1,000,000 Hz or is it 1,048,576 Hz (1,024 Hz * 1,024)?
Hz are always SI units Mega = 10^6 or one million.
Strictly speaking 2^20 should use the Mi (Mebi) prefix for all applications. I know that those prefixes were codified rather late, but it was still in the 1990's and have been in popular usage for over a decade.
kilo = 1024 only for memory size terms, for others its kilo = 1000. Hope it answers your question.