Editing AVR microcontrollers (section)

=== MCU speed ===
The AVR line can normally support clock speeds from 0 to 20&nbsp;MHz, with some devices reaching 32&nbsp;MHz. Lower-powered operation usually requires a reduced clock speed. All recent (Tiny, Mega, and Xmega, but not 90S) AVRs feature an on-chip oscillator, removing the need for external clocks or resonator circuitry. Some AVRs also have a system clock prescaler that can divide down the system clock by up to 1024. This prescaler can be reconfigured by software during run-time, allowing the clock speed to be optimized.

Since all operations (excluding multiplication and 16-bit add/subtract) on registers R0–R31 are single-cycle, the AVR can achieve up to 1 [[Million instructions per second|MIPS]] per MHz, i.e. an 8&nbsp;MHz processor can achieve up to 8&nbsp;MIPS. Loads and stores to/from memory take two cycles, branching takes two cycles. Branches in the latest "3-byte PC" parts such as ATmega2560 are one cycle slower than on previous devices.