A microprocessor is a Silicon Chip that performs all the operations in the computer. The moment the computer is powered on, the processor swings into action and performs all the instructions. All instructions to the processor, from booting, word processing, games and everything done on the computer are reduced to a set of instructions the microprocessor can do.
The instructions are memory pointers and are stored in small memory locations in the processor called Registers and the processor executes these instructions. Basically, when an operating system is installed on the computer, the operating system reduces the instructions and tasks to instructions that the processor can understand. The instructions differ for various processors. The processors from Motorola and Intel follow different instructions.