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)?

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    \$\begingroup\$ outside of computer memory applications the si units are actual SI units. So Hz will be correct. \$\endgroup\$
    – Kortuk
    Feb 21, 2013 at 2:48
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    \$\begingroup\$ You would be better served to use an external crystal. The internal oscillator is awful. \$\endgroup\$
    – Matt Young
    Feb 21, 2013 at 2:49
  • \$\begingroup\$ @MattYoung Thanks for the tip. I wondered one time why my AVR timer circuit was off by a couple seconds per minute. ;) \$\endgroup\$
    – BenjiWiebe
    Feb 21, 2013 at 2:53
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    \$\begingroup\$ Nobody's insane enough to invent binary versions of hertz and still call them hertz, thank god. \$\endgroup\$ Feb 21, 2013 at 11:07
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    \$\begingroup\$ Most, if not all, AVR has the ability to slightly change the internal RC oscillator frequency by programming a register. You can use that register to get closer to the desired frequency, hence user calibration. \$\endgroup\$
    – jippie
    Feb 21, 2013 at 22:01

2 Answers 2


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.

  • \$\begingroup\$ Yes but only for coding purposes does kilo=1024. If you buy memory sticks or drives they use the SI value as a short hand. Read the small print for actual memory size. \$\endgroup\$ Feb 27, 2013 at 3:28

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