Difference Between 计算机 and 电脑
In most cases, they're interchangable and both mean personal computer.

计算机 could be used for wider range. Such as,



大型计算机 (large (-scale) computer; maxicomputer)
中型计算机 (medium-size computer; midcomputer)
小型计算机 (minicomputer; small-size computer)
微型计算机 (microcomputer)