IV. STORAGE HARDWARE

Storage hardware provides permanent storage of information and programs for retrieval by the computer. The two main types of storage devices are disk drives and memory. There are several types of disk drives: hard, floppy, magneto-optical, magnetic tape, and compact. Hard disk drives store information in magnetic particles embedded in a disk. Usually a permanent part of the computer, hard disk drives can store large amounts of information and retrieve that information very quickly. Floppy disk drives also store information in magnetic particles embedded in removable disks that may be floppy or rigid. Floppy disks store less information than a hard disk drive and retrieve the information at a much slower rate. While most computers still include a floppy disk drive, the technology has been gradually phased out in favor of newer technologies.

Magneto-optical disk drives store information on removable disks that are sensitive to both laser light and magnetic fields. They can store up to 9.1 gigabytes (GB) of data, but they have slightly slower retrieval speeds as opposed to hard drives. They are much more rugged than floppy disks, making them ideal for data backups. However, the introduction of newer media that is both less expensive and able to store more data has made magneto-optical drives obsolete.

Magnetic tape drives use magnetic tape similar to the tape used in VCR cassettes. Tape drives have a very slow read/write time, but have a very high capacity; in fact, their capacity is second only to hard disk drives. Tape drives are mainly used to back up data.

Compact disc drives store information on pits burned into the surface of a disc of reflective material (see CD-ROM). CD-ROMs can store up to 737 megabytes (MB) of data. A Compact Disc-Recordable (CD-R) or Compact Disc-ReWritable (CD-RW) drive can record data onto a specialized disc, but only the CD-RW standard allows users to change the data stored on the disc. A digital versatile disc (DVD) looks and works like a CD-ROM but can store up to 17.1 GB of data on a single disc. Like CD-ROMs, there are specialized versions of DVDs, such as DVD-Recordable (DVD-R) and DVD-ReWritable (DVD-RW), that can have data written onto them by the user. More recently Sony Electronics developed DVD technology called Blu-ray. It has much higher storage capacities than standard DVD media.

Memory refers to the computer chips that store information for quick retrieval by the CPU. Random access memory (RAM) is used to store the information and instructions that operate the computer's programs. Typically, programs are transferred from storage on a disk drive to RAM. RAM is also known as volatile memory because the information within the computer chips is lost when power to the computer is turned off. Read-only memory (ROM) contains critical information and software that must be permanently available for computer operation, such as the operating system that directs the computer's actions from start up to shut down. ROM is called nonvolatile memory because the memory chips do not lose their information when power to the computer is turned off.

A more recent development is solid-state RAM. Unlike standard RAM, solid state RAM can contain information even if there is no power supply. Flash drives are removable storage devices that utilize solid-state RAM to store information for long periods of time. Solid-state drives (SSD) have also been introduced as a potential replacement for hard disk drives. SSDs have faster access speeds than hard disks and have no moving parts. However, they are quite expensive and do not have the ability to store as much data as a hard disk. Solid-state RAM technology is also used in memory cards for digital media devices, such as digital cameras and media players.

Some devices serve more than one purpose. For example, floppy disks may also be used as input devices if they contain information to be used and processed by the computer user. In addition, they can be used as output devices if the user wants to store the results of computations on them.