Modern Computers
Modern computers are electronic and digital. The actual machinery -- wires, transistors, and circuits -- is called hardware; the instructions and data are called software.All general-purpose computers require the following hardware components:

• Memory: enables a computer to store, at least temporarily, data and programs.
• Mass storage device: allows a computer to permanently retain large amounts of data.      Common mass storage devices include disk drives and  tape drives.
• Input device: usually a keyboard and mouse, the input device is the conduit through which data and instructions enter a computer.
• Output device: a display screen, printer, or other device that lets you see what the computer has accomplished.
• Central processing unit (CPU): the heart of the computer, this is the component that actually executes instructions.