Computer hardware refers to the physical components of a computer system and includes devices like circuit boards, chips, monitors, disks, and disk drives. Early mechanical calculators used gears like clocks, while the ENIAC, built in 1945, was one of the first electronic general-purpose computers and was used to calculate ballistic missile trajectories. Computer hardware has various functions including storage using volatile and non-volatile memory, processing data through microprocessors and parallel or distributed processing, and input/output through devices like keyboards, mice, monitors, and printers. The core internal computer parts are the motherboard, processor, memory, hard disk, and expansion cards.