A 533 Mhz CPU will not work in a 400 Mhz motherboard. While it is not necessary that a CPU operate at the same frequency as the motherboard, its speed must be a multiple of the motherboard speed.
Function
According to the website Directron, CPUs attain their full speeds with the aid of devices called "multipliers." These allow CPUs to complete a number of operations, or "cycles," for every motherboard cycle. Setting the CPU speed to a multiple of the motherboard speed allows it to run faster while still working in sync with the board.
Misconceptions
The misconception that CPUs can work in slower motherboards whether or not their speed is a multiple of the board's speed partially comes from the fact that this is true for system memory. According to the Crucial website, memory typically works in boards slower than those for which they were intended. The board simply slows down the memory speed to match its own.
Considerations
When selecting a CPU, look at its front side bus speed as well as its multiplier. Find a motherboard with the same speed as the processor's FSB. The multiplier tells you how many times faster than the FSB the processor will run.
Tags: motherboard speed, multiple motherboard, multiple motherboard speed, speed multiple