Data Storage

Part 3 - Storage Devices

This is a summary of the most common types of storage devices.

Fixed Storage Devices

Hard Disk Drive(HDD) is a storage device that stores large amounts of data. HDD's use a series of magnetically coated disks that store data as ones and zeros. One type of HDD is fixed, which is mounted inside your computer. Although Considerd Fixed Devices, it is now fairly easy to have HDD's that are removeable. These includes drives which hook up to USB or Firewire ports on your computer, or Even ones that have Special Slots (like Removable HDD Trays). Newer HDD's have storage capabilities that are in the 100's of gigabytes range.

Drive Arrays are basically made up of multiple physical disks, that look like a single Logical disk. They are very similar to HDDs in many ways, and in fact many server systems and even high performance systems use them for Speed and/or Redundancy. The system sees the Array of Disks as a single HD. There are many types of Drive Arrays, and different technologies, however they are beyond the Scope of this course. Some Common Devices that utilies Arrays are Storage Area Networks - SAN, Network Attached Storage - NAS, Redundant Array of Independant Disks - RAID, as well as others.

Removable Storage Devices

On the other hand in order to share information, there was the need for Removable Storage

Floppy Disks are a removable plastic disk that stores small amounts of data. This was a very popular type of storage due to its low cost and wide availability. Currently Standard 3.5" floppy disks, commonly used on many home computers can hold 1.44 megabytes of data. Originally Floppy Disks were 8" in size, and sored only about 180 KB.

Compact Discs are optical disks that store medium to large amounts of data. Most CDs can be written to only once, but read from infinite times (provided the CD is in good condition). However with the dawn of the new CD writting technology, there are also CDs that can be written and rewritten to many times. CDs can hold anywhere from 540MB to 800MB of data.

Tape is a magnetic media that is commonly used for backup purposes today. It is a slow media for accessing data, but its large capacity and low cost make it ideal for backing up large amounts of data. The storage capacity of tape ranges greatly from a few hundred megabytes, to Gigabytes or even Terabytes when information is compressed. Tapes were the Original Storage Device before Random Access devices like Floppy Disks and Hard Disk were invented.

Solid State Storage - also known as Memory Cards used in Cameras and other portable devices, as well as Flash memory, used in USB Keys are forms of Solid State Storage. Basically they use Static RAM technology and in recent years have gained in capacity, wilste the price has been dropping.

Basic Data Amounts

Here is a basic conversion chart for storage quantities and their equivalents: