Storage Devices

A storage device is any device used by a computer to store information permanently, in contrast to memory, which is used to store information temporarily. Storage devices can be divided into two categories: fixed and removable.

The commonest fixed storage devices are hard disk drives (HDDs), non-volatile devices that store information on magnetic platters. Modern hard disks vary in capacity from 250GB to 2TB and have speeds of 7200 – 10000 RPM. They can be connected to a computer in two different ways: Parallel ATA (PATA) or Serial ATA (SATA).

Parallel ATA (also known as Integrated Drive Electronics (IDE)) was the interface commonly used on older computers. The cable used to connect drives to the motherboard was a flat, wide ribbon cable. You can find out more by reading the Wikipedia article on Parallel ATA.

Serial ATA offers faster communication speeds between the drive and the motherboard and uses a much smaller ribbon cable. You can find out more by reading the Wikipedia article on Serial ATA.

SCSI (Small Computer Systems Interface), pronounced “scuzzy”, is a different type of interface allowing several devices to be daisy-chained. You can find out more by reading the Wikipedia article on SCSI.

RAID (Redundant Array of Independent Disks) is a system that uses multiple hard disks which share data across the drives. It enhances data security and recoverability and helps protect against hard drive failure. You can find out more by reading the Wikipedia article on RAID.

Floppy Disk Drives (FDD) were an older form of removable storage that used a thin, flexible magnetic storage medium, encased in a plastic shell to read and write data. They are no longer in common use, having been replaced by cheaper and higher capacity optical drves and devices like flash memory drives and SD Cards.

Optical Drives (CD-R and DVD-R) use a laser to  “burn” data onto blank optical discs.There are several different types of optical media:

CD-R: can only be written once. The standard capacity is 700MB. The rewriteable version is known as CD-RW.

DVD-R: write-once discs with a standard capacity of 4.7 GB. The rewriteable version is DVD-RW. Dual-layer disks, with a capacity of almost 8.55 GB are known as DVD+RW DL.

Blu-Ray: an optical disc storage medium designed to replace the original DVD format can store 25 GB of data on a single-layer disk and 50 GB on a dual-layer disk.

Drive speeds are are normally expressed as multiples of the original read speed of the device: 150KB/s for CD-R and 2.54KB/s for DVD-R. Thus, a 52x CD-ROM reads at 7800KB/s, and a 16x DVD-ROM reads at 21,640KB/s.

Other removable storage options include:

Tape Drives: sequential-access media composed of a strip of magnetic tape. They are still used occasionally for backup or long-term storage due to their long shelf-life.

Solid State Drives (SSD) such as thumb, flash and SD drives have no moving components and have extremely rapid access speeds. They were initially small, hand-held devices, but are increasingly used as replacements for magnetic hard disks, with capacities of up to 500 GB.

Next: I/O Devices