All those components of computer system that are tangible and on which either input could be given (like keyboard and mouse etc.) or output could be received (like monitor and printer etc.) are known as computer hardware. These hardware components of computer system themselves do not generate instructions but process the instructions generated by either software or user.
Computer hardware is only a subset of word hardware that is when we say computer hardware we only mean the hardware used in computer system but if we say only hardware we mean all the hardware that can be used in any machine. Computer hardware includes following parts in computer system like: keyboard, mouse, floppy drive, hard disk, CD Drive, printer, RAM etc.
But do the hardware alone makes the computer system not it is wrong. A computer system with hardware and without software is life less that means it is same as like a skeleton without life. To make a computer system fully functional software is essential with the hardware. The very basic software that is required for making computer to work in a friendly manner and making it to support all the user activities is operating system.