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Removable Storage Reference

Accessing data from a disk is not as fast as accessing data from main memory, but disks are much cheaper. And unlike RAM, disks hold on to data even when the computer is turned off. Consequently, disks are the storage medium of choice for most types of data.

Regardless of how big hard drive capacities get, there will always be a need for removable storage, sometimes called portable storage. The software you buy to install on your computer comes on removable storage media and people will always have a need for making backups and archiving important data or transporting data between computers. These are just a few examples of how we use removable storage in everyday computing environments.

Removable storage is not a new concept in the computer industry. Since the early 1980's we have seen the standard floppy disk drives with the removable 3.5 inch diskettes. As computers and technologies have advanced over the years, removable storage technology has moved right along as well. From a 1.44MB capacity we now see removable storage with the capacity to hold more 20GB of data.

Removable storage can be broken down into three categories, based on the technology used by the device to record and store data on the removable media.

The first and oldest technology is in the form of magnetic drives, which includes removable media storage such as floppy drives, hard drives, Zip and Jazz drives. Secondly, we have optical drives, which is a collection of removable storage options such as CD-ROM, DVD, and Magneto-Optical Drives. Most recently we have seen removable storage take a new turn as the consumer's love of digital cameras and other portable electronic devices has emerged. The third category of removable storage we cover highlights flash memory storage options, which is also called solid state storage because the drives contain no moving parts.

Removable Storage — Magnetic Drives
On magnetic disks the data is encoded as microscopic magnetized needles on the disk's surface. You can record and erase data on a magnetic disk any number of times.

In its infancy, magnetic drives were used largely for back-up and archiving. With today's high-capacity hard disks, however, you would need countless floppy disks to backup a system — even a 2GB Jaz drive isn't suited to archiving. The category of magnetic drives, however, still has its place in everyday computing as a means for storing smaller applications, documents and small databases. One key issue to consider when choosing a type of magnetic removable storage device is compatibility. You may choose a Jaz drive for your removable storage needs, but those who need to share the data with may not have a Jaz drive on which to read your disk.  One area of concern for those who choose magnetic removable storage is that the drives are made up of many mechanical parts and you risk a chance of having the device malfunction. Additionally, magnetic media is quite vulnerable to environmental degradation.

Some Common Types of Magnetic Drives

Floppy Drive: [View Webopedia Definition]
Floppy drives are portable and are a universal file storage solution. The standard size of a floppy is 1.44MB on a 3.5" floppy disk. Floppy disks are the perfect solution for backing up small files, or for copying files for use on another computer that is not on your network. Due to the small amount of data they can hold, however, it would seem as if floppies are on their way out. Today, when you purchase a new PC it may not come with a 3.5" floppy drive. Floppy drives and floppy disks are quite cheap, and very portable, which still makes them worth having for small file and application storage.

Hard Drive: [View Webopedia Definition]
The hard drive is the main area of mass storage on your computer. Generally the hard drive is fixed within the computer, making it removable, but not easily portable. Storage capacities can range into the gigabytes, and over the years we've seen hard drives come down in price considerably. Unlike a floppy drive, there is no hard drive diskette, so you have to install the hard drive into another computer to share files.  There are portable hard drives (also called pocket hard drives) available however, which can be plugged into a USB drive and offer upwards of 80GB of storage.

SuperDisk:  [View Webopedia Definition]
Developed by Imation Corporation, SuperDisks are similar to the floppy drive, but they support very high-density diskettes. As opposed to the  conventional 3.5-inch 1.44 MB disks, the SuperDisk allows for a 120 MB capacity on one disk. Additionally SuperDisk is backward compatible with older diskettes. This means that you can use the same SuperDisk drive to read and write to older 1.44 MB diskettes as well as the 120 MB SuperDisk diskettes.

Jaz Drive: [View Webopedia Definition]
The Jaz drive is a removable storage solution developed by Iomega Corp. The Jaz drive has a 12-ms average seek time and the removable cartridges hold up to 2 GB of data. The fast data rates and large storage capacity make it a viable alternative for backup storage as well as everyday use. Jaz disks are very portable making the Jaz a popular choice for removable storage media.

Magnetic Tape  [View Webopedia Definition]
A tape drive is similar to a tape recorder in that it reads data from and writes it onto a tape. Tape drives have data capacities of anywhere from a few hundred kilobytes to several gigabytes, and varying transfer speeds as well. While tapes are a very portable removable storage solution, the disadvantage of tape drives is that they are sequential-access devices, which means that to read any particular block of data, you need to read all the preceding blocks. This makes them much too slow for general-purpose storage operations, but are a good choice for archiving and back-up tasks.


Removable Storage — Optical Drives

Optical disks record data by burning microscopic holes in the surface of the disk with a laser. To read the disk, another laser beam shines on the disk and detects the holes by changes in the reflection pattern.

Most modern PCs come with a form of optical drive; mainly the CD-ROM. At one time having a CD-ROM was something you would find only on a high-end computer, but as the performance of the drive increased and costs decreased, the CD-ROM has replaced the floppy drive as the main device for installing software. The  rewritable CD-ROM is currently the most popular backup and file-sharing removable storage device.

Some Common Types of Optical Drives

WORM  [View Webopedia Definition]
WORM is an acronym for for write once, read many. Commercially available since the early 1980s, WORM disks are a nonerasable disk that today can offer up to 20GB of storage capacity on a single disk. While WORM disks are very portable, their inability to erase data written to the disk make this removable storage a favorite for archival purposes. WORM disks require a specific software (or hardware) interface to be read, and usually you will find WORMS used in data archiving of legacy systems where a WORM-based file system is designed and implemented.

Magneto-Optical Drives [View Webopedia Definition]
Abbreviated as MO, Magneto-Optical drives a type of data storage technology that combines magnetic disk technologies with optical technologies; MO drives write magnetically and read optically. MO disks can hold upwards of 200MB of data with newer media and drives providing over 1.2GB of storage. MO drives can access data access  faster than magnetic devices and faster than a CD-ROM; they are also reliable and resilient against normal wear damage and environmental damage. Older MO systems required you to erase data from the MO disk before writing new data to it, however newer drives speed up the rewriting process by allowing you to write data overtop of old data in one step. MO disks are highly portable and, like WORMs, are often used in data archiving of legacy systems. Because an MO disk is rewritable, they are also a popular media for system back-ups.

CD-ROM & CD rewritable [View Webopedia Category]
Short for Compact Disc-Read-Only Memory, a CD-ROM is an optical disk capable of storing large amounts of data. The CD-ROM has replaced the floppy disk as the media for software distribution, as it has the storage capacity to hold as much data as 700 floppy disks. In recent years, rewritable CD-ROMs (called CD-R drives, or more commonly, CD burners) have emerged as the removable storage device of choice for many homes and businesses. CD-R drives allow users to record information to a CD (compact disk), providing an easy way to archive data or share files. Additionally, you can choose CD-RW disks that allow you to write data to the CD multiple times. 

DVD-ROM & DVD rewritable [View Webopedia Category]
Short for digital versatile disc or digital video disc, a DVD is type of optical disk technology similar to the CD-ROM. A DVD holds a minimum of 4.7GB of data, enough for a full-length movie. DVDs are commonly used as a medium for digital representation of movies and other multimedia presentations that combine sound with graphics. Similar to CDs, DVDs are rewritable and media can be found as DVD+R, DVD-R (record to the DVD once), and DVD+RW where the disc can be erased and recorded over numerous times. In terms of price, CD-ROMs are still cheaper but we have seen the price of DVD-ROMs, DVD burners, and DVD media come down in price over the years. It is expected that DVDs will replace the CD-ROM as the removable storage device of choice.

Flash Memory (Solid-State Removable Storage)  [View Webopedia Definition]
Abbreviated SSD, a solid state disk is a high-performance plug-and-play storage device that contains no moving parts. Flash memory, commonly found in digital cameras, is considered a type of removable solid-state storage. Flash memory is small, light and fast. Due to its cost and capacity, however, it is used mainly in laptops, digital cameras, digital audio players, hand-held computers and video game consoles. Flash memory works a lot like your computer's memory, but acts like a hard drive in terms of being able to store data.

Some Common Types of Removable Flash Memory

SmartMedia
SmartMedia is a
a removable flash memory card  that is a very small and thin storage card, used mainly in electronic devices like a digital camera, MP3 player or PDA. SmartMedia cards can hold up to 128MB of data and have a high-transfer rate for copying and downloading. SmartMedia cards are an excellent media for storing music or image files for transferring from an electronic device to your PC.

CompactFlash [View Webopedia Definition]
Invented by SanDisk Corporation in 1994, a CompactFlash card is a very small removable mass storage device that relies on flash memory technology.
The CompactFlash card is about the size of a matchbook and only weighs half an ounce. CompactFlash is a popular choice for removable storage used in electronic equipment like digital cameras, handheld PCs, and digital audio players. CompactFlash offers storage up to 1GB.

USB Flash Drives  [View Webopedia Definition]
A USB flash drive is a very small, portable flash memory card that plugs into a computer's USB port and functions as a portable hard drive with up to 2GB of storage capacity. USB flash drives are touted as being easy-to-use as they are small enough to be carried in a pocket and can plug into any computer with a USB drive, making them a excellent choice for file sharing and for use in small electronic devices.


Vangie 'Aurora' Beal - Writer, www.Webopedia.com
Last updated: February 11, 2005

Related Links

OSTA - Optical Storage Technology Association (PDF)
This OSTA white paper offers comprehensive information on  Data Interchange and Optical Standards

Webopedia Data Storage Category
A comprehensive listing of terminology related to removable data storage.

Fujitsu's MO History
From 1982 to 2002, this quick reference outlines the advances of Fujitsu's MO developments.

Enterprise IT Planet
The source for Storage, Security and Networking Resources for the IT professional.

Webopedia's Did You Know: What's Inside a Hard Drive
All hard drives share a basic structure and are composed of the same physical features. However, not all hard drives perform the same way as the quality of the parts of the hard drive will affect its performance.

Webopedia's Did You Know: DVD Formats Explained
The following information sheds some light on DVD's different flavors, the differences between them and the incompatibility issues that the differing technologies have sprouted.

DISK/TREND NEWS: Optical and removable disk drives
Computer growth markets attract a diverse group of disk drives, including both winners and losers.



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