Where does the most calculations done in a computer take place in?

The Arithmetic Logic Unit (ALU) inside the Central Processing Unit (CPU) of the computer.

Most modern computers however do not have a single general purpose ALU that handles everything, but instead have several independently functioning special purpose ALUs optimized for specific data types (e.g. integer numbers: I-ALU, floating point numbers: FP-ALU, boolean logical values: LU).