Removable Storage
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Removable Storage

by George Hernande

Removable storage is computer storage memory that can be switched out easily. EG: A floppy disk is removable storage but the hard drive is not considered to be removable storage.

The various kinds of removable storage technologies include:

Magnetic Disk

Data is read from and written onto a surface embedded with minute magnetic particles by a head. In hard drives, the head floats above the surface, while in a floppy disk the head rides on the surface.



Data is read and written with laser onto a material protected by a substrate. High capacity storage immune to magnetic and other environmental dangers. This includes CDs (Compact Disc), WORMs (Write Once Read Many), EOs (Erasable Optical), MD (Mini Discs), and DVD (Digital Video Disc).



(Magneto-Optical). Data is written by bringing points to the Curie point (approximately 200 C) via laser and then data encoding the point via a magnetic head. Data is read by a laser taking advantage of the Kerr Effect, i.e. the difference in the polarity of reflected light depending on the orientation of magnetic particles.

  • 5.25 in @ 2.6 GB.
  • 3.5 in @ 128 MB - 230 MB - 530 MB - 640 MB - 1.3 GB



(Light Intensity Modulated Direct OverWrite). Like MO except that instead of a magnetic head, the temperature of the laser can reverse the polarity of magnetic layers within the disk itself. Thus LIMDOW is faster because it only takes one pass in contrast with MO's two passes.

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Phase Change

Data is written via heating pits via laser. The laser can amorphize the spot, or, upon reheating return the spot to its originals state by recrystallization. This is technology utilized by Panasonic's PDs (Phase change Disks).



Data is read and written to a memory chip. These are usually quickly accessed by the USB port.

Except for magnetic disk technology, the removable storage technologies are usually used for static data. EG: CDs are usually written onto once.

Floppy disk

Current version spins at 300 rpm with 135 tracks/inch. These magnetic disks store bits via magnetic inversions at intervals of 2-4 microseconds along its tracks.

5.25 inch at different capacities:

  • 160 kB (1981)
  • 180 kB
  • 360 kB (double sided)
  • 1.2 MB

3.5 inch at different capacities:

  • 720 kB (1984)
  • 1.44 MB (1987)

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Memory sticks

8 MB to 512 MB. These are flash memory storage sticks that usually plug into a USB port.

  • M-System makes the thumb-sized DiskOnKey product (2002) which is USB 2 compliant and has a 1 MB/s transfer rate.
  • ThumbDrive makes the ThumbDrive product (2002) which reads at 700 KB/s and writes at 350 KB/s. The ThumbDrive also has access security by fingerprint.


Floppy replacement

100 MB to 150 MB

  • 3.5 in Iomega Zip Disk, 94 MB (1995), magnetic disk with 3000 rpm. 1 MB/s data transfer and 29 ms seek time. Utilizes the Bernoulli aerodynamic principle where the flexible surface is sucked up to the read/write head. Interfaces via parallel port, SCSI, ATAPI, or USB. In wide use in 1999.
  • 3.5 in Imation Super Disk LS-120 (Laser Servo), 120 MB (1998) magnetic disk with 720 rpm. 450 KB/s data transfer and 70 ms seek time, i.e. 5 times faster than a floppy but slower than a Zip Disk. Backwards compatible to floppy disks. Interfaces via IDE. Recognized by BIOSes as a fail-safe start up drive.  2490 tracks/inch.
  • 3.5 in Sony HiFD, 200 MB (1999) magnetic disk with 3600 rpm. 3.6 MB/s data transfer. Backward compatible with floppy disks



Supper floppy

200 MB to 300 MB. Magnetic or MO devices. Includes Iomegas 237/250 MB Zip Disk.


Hard disk complement

500 MB to 1 GB. Magnetic, MO, and phase change devices. Like a hard disk partition. May function as a secondary but slow hard disk.


Removable hard disk
  • 1 GB plus. Magnetic, MO, and phase change. Like small, fast hard disks.
  • Iomega Jaz Disk, 1-2 GB (1996). 5.4 MB/s data transfer and 12 ms seek time. Interfaces via IDE, SCSI, and Ultra SCSI.
  • SyQuest's SyJet, 1.5 GB (1997) and 1.0 GB SparQ (1998). Bought out by Iomega.
  • 3.5 in Castlewood Systems ORB, 2.2 GB (1999). 12.2 MB/s and 12 ms seek time. Fast enough to stream audio and video! Runs cooler than the Iomega Jaz. Interfaces via parallel port, USB, SCSI, Ultra SCSI, and EIDE.

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