Output Devices

Output devices allow us to see the results of the computer's processing. A common output device is the monitor or video display, which provides what is known as soft copy, or one that we can only view but cannot keep. Whenever we type a character on the keyboard, we see it output to the monitor. Another output device is the printer, which gives us hard copy, a permanent paper record. Printing begins when we issue the proper software instruction.

Storage Devices

Storage devices, also known as auxiliary storage, are used to keep instructions (in the form of programs) and data permanently. A common auxiliary storage device is the disk drive. It can copy data that is being held in RAM onto a magnetic disk; this is called writing to the disk. The disk drive can also copy instructions or data from the disk into RAM so that the computer can perform its processing; this is called reading from the disk.

Media.

The two most common types of auxiliary storage media for personal computers are magnetic disks. There is the floppy disk; the two most common types are the 5¼-inch disk and the 3½-inch disk. People can insert and replace floppy disks in an auxiliary storage device, which of course is called a floppy disk drive. Just beneath the two floppy disk drives is the hard disk drive, which has a rigid magnetic disk enclosed in a permanently sealed housing. Hard disk drives have greater capacity than floppy disk drives. Both types of drives are connected to a controller circuit board, or card, which is plugged into an expansion slot in the motherboard.

Auxiliary storage, also called auxiliary memory or secondary storage, is memory that supplements RAM. This type of memory is long-term, nonvolatile memory. Nonvolatilemeans it stores and retains programs and data regardless of whether the computer is turned on or off.

RAM is auxiliary storage's working partner. In fact, RAM is sometime called the "working memory" of the computer because it holds the data and instructions during data processing. RAM is read-write memory: it can read write data and instructions to auxiliary storage. We use this example to see how the two different kinds of memory work together:

Input .You type a short memo that reads, "Department meeting at 3:00 p.m. today."

Processing. The CPU executes the instructions to turn the keystrokes into characters.

Output. The characters are displayed on the monitor.

Storage. The memo is stored temporarily in RAM.

Results. You want to post the memo on the bulletin board, so you send it to the printer for a paper copy.

Storage. At this point, you could also send the memo from RAM's working memory to a storage device, where you could save it permanently.

Computers differentiate between main storage and auxiliary storage in terms of speed and efficiency. RAM storage is very fast, because it's usually on a chip or circuit board physically close to the CPU. The shorter the distance electrical signals have to travel, the faster the processing. Auxiliary storage is usually slower, not only because of the electrical distance, but because it involves some type of mechanical operation. For instance, disk drives must spin the disk to store data.