If there are cache misses, NAN errors, etc., the number of clock cycles for the DIV instruction can result in 100 cycles or more being added to the time required to perform the operation. The DIV instruction to carry out the base 10 math will end up executing at least 4 times longer than doing SHR instructions for the base 2 math (minimum of 41 cycles as opposed to a maximum of 10).
The advantage of using base 2 math means that the code is somewhat simpler and it will run faster. Drive manufacturers report drive sizes using base 10 math while computer operating systems tend to report these sizes using base 2 math.
