1.1 Main Components of a Computer
1.1.1 Main components of a computer
The four main components of a computer are the Random Access Memory (RAM), the Central Processing Unit (CPU), the Input/Output (I/O), and the hard disk or other mass storage devices.

Random Access Memory (RAM)
Random Access Memory in the form of microchips is normally located on the motherboard or the memory board of the computer. It is the main computer memory, often referred to as primary memory or working memory. Primary memory is that part of memory where the activity of the running system takes place. When you hear, "My system has 64 MB (Megabytes) of memory," the speaker is talking about primary memory or RAM.

Operating systems and software programs usually reside on the hard disk. When the computer is started (booted), an image or copy of the operating system is loaded into RAM. Similarly, when a program is activated, an image or copy of that program is loaded into RAM. Images in RAM remain as long as they are needed. Once these images are no longer required, they are overwritten by other images. If power is lost or the system is rebooted, images in RAM disappear.

Central Processing Unit (CPU)
The Central Processing Unit is the computer's logic microprocessor chip that executes instructions (processes) received from the primary computer memory (RAM). These instructions are stored in binary language.

Input/Output (I/O)
The Input/Output portion of the computer accepts or reads input from a device (such as your keyboard) into memory, or it writes output from memory to a device. For example, the keyboard and the mouse are the primary user input devices; the monitor, printer, and tape drive are the primary output devices. Disk drives are considered both input and output since they can be both read from and written to.

Hard Disk (or Other Forms of Mass Storage)
The hard disk is a magnetic storage device where information is stored. All files, including the operating system and applications or utilities, are stored on a hard disk. The contents of the hard disk are managed by the File System, which will be covered later.