Which regions use 计算机 for computer?
计算机 is often used for computer in written language in mainland China. And 电脑 usually means Desktop computer in oral language.
Calculator is 计算器 not 计算机 just as @StarCub said.
And for laptop, it's 手提电脑, 笔记本电脑, or just called 笔记本(not the notebook here).
Usually, 超级计算机 is used for supercomputer. But generally speaking, supercomputer often has its own name, just like 天河一号(Thiahe-1A).