Computer hardware refers to the physical components of a computer system. It includes both internal components like the motherboard, hard drive, and RAM, as well as external components like monitors, keyboards, mice, and printers. Computer hardware can be classified into four categories: input devices, processing devices, output devices, and memory/storage devices. Input devices like keyboards and mice allow a user to input information. Processing devices like the CPU and GPU process instructions. Output devices like monitors and printers display or print the processed information. Memory and storage devices like RAM, hard drives, and flash drives temporarily or permanently store files and data.