why page frame is multiple of 2 in virtual memory?

Answer 1

Numbers within a computer are stored in binary format, meaning the only use the digits 0 and 1. Place value is used to determine that value of a "1". Like in "regular" numbers, "10" is ten times as much as "1", "100" is ten times as much as "10", etc.

In binary, each new "place" is 2 times as much (1=1, 10=2,100=4, 1000=8, 10000=16, etc). When you assign a page frame, it has to be a 1 followed 0s. So the page frames go up in size by multiples of 2. If you were to assign a frame that was not a multiple, your computer would still assign the next maultiple of 2, but then not use the entire space. You would be wasting hard drive and memory. So instead it forces you to use multiples of 2.