Microprocessors are central processing units contained on a single chip. They power modern computers and digital devices. A microprocessor has several components including a control unit, arithmetic logic unit, registers, instruction decoder, and bus interface unit. It communicates with memory and peripherals using an instruction set and addressing modes. Interfacing devices like USART, PPI, and DMA controllers allow microprocessors to connect to external components and transfer data. Interrupts and polling allow microprocessors to multitask and respond to events. Microprocessors have evolved over generations from 4-bit to 64-bit designs, increasing capabilities.