Why a super computer is the same as a mainframe computer?
It is not. The fastest super computers are typically much smaller physically than mainframe computers to keep signal paths short and processing speeds fast. A signal can not travel more than 1 foot in a wire in 1 nanosecond and modern super computers can do many many instructions in that time. Long wire runs limit the processing speed of any computer and must be avoided in super computers, they don't much matter in typical mainframes. Super computer designers often use extreme packaging technologies and cooling systems not used by other computers to do this.