Modern computer hardware is divided into two categories: main hardware and peripherals. Peripherals are then subdivided into input, output and storage devices. Main hardware components are technically the only requirement for a computer to work, but computers would not be of much use without peripherals. Normally, modern computers employ both.
Main hardware includes the pieces a computer needs to run, namely a central processing unit, or CPU, random access memory, or RAM, and read-only memory, or ROM. These components are at the core of any computer. Output peripherals are those that show data to a user, such as a monitor and a printer. Input peripherals are those that receive data from the user, such as a keyboard and a touchpad or mouse. Storage devices include hard drives and CD/DVD/BluRay drives.