Removable Storage

Removable storage has been around almost as long as the computer itself. Early removable storage was based on magnetic tape like that used by an audio cassette. Before that, some computers even used paper punch cards to store information.

We've come a long way since the days of punch cards. New removable storage devices can store hundreds of megabytes (and even gigabytes) of data on a single disk, cassette, card or cartridge. There are several reasons why removable storage is useful: it’s commercial software, you can make back-up copies for storing software and information that you don't need to access constantly, it’s possible to transport data between two computers (e.g. copying information to give to someone else), you can secure information that you don't want anyone else to access.

Modern removable storage devices offer an incredible number of options, with storage capacities ranging from the 1.44 megabytes (MB) of a standard floppy to the upward of 700 gigabyte (GB) capacity of some portable drives. All of these devices fall into one of three categories: magnetic storage, optical storage, solid-state storage.

Magnetic Floppy disc

The most common and enduring form of removable-storage technology is magnetic storage. For example, 1.44-MB floppy-disk drives using 3.5-inch diskettes have been around for about 15 years, and they are still found on many computers sold today. In most cases, removable magnetic storage uses a drive, which is a mechanical device that connects to the computer. You insert the media, which is the part that actually stores the information, into the drive.

Just like a hard drive, the media used in removable magnetic-storage devices is coated with iron oxide. A disk is made from a thin piece of plastic coated with magnetic material on both sides. On the disk there are tracks. The tracks are arranged in concentric rings so the software can jump from "file 1" to "file 19" without having to fast forward through files 2 through 18. The disk spins like a record and the heads move to the correct track, providing what is known as direct-access storage.

The read/write heads ("writing" is saving new information to the storage media) do not touch the media when the heads are traveling between tracks. There is normally some type of mechanism that you can set to protect a disk from being written to.

Hard disc

Hard discs were invented in the 1950s. They started as large discs up to 20 inches in diameter holding just a few megabytes. They were originally called “fixed discs” or “Winchesters”. They later became known as “hard discs” to distinguish them from “floppy discs”. Hard discs have a hard platter that holds the magnetic medium, as opposed to the flexible plastic film found in tapes and floppies.

A typical desktop machine has a hard disc with capacity of between 60 and 400 gigabytes. Data is stored onto the disc in the form of files. A file is simply a named collection of bytes. The bytes might be codes for the characters of a text file, or they could be instructions of a software application for the computer to execute, or they could be the records of a data base, or they could be the pixel colors for a GIF image. No matter what it contains, however, a file is simply a string of bytes. When a program running on the computer requests a file, the hard disc retrieves its bytes and sends them to the CPU one at a time.

A hard disc itself is a sealed aluminum box with controller electronics attached to one side. The electronics control the read/write mechanism and the motor that spins the platters. The electronics also assemble the magnetic domains on the drive into bytes (reading) and turn bytes into magnetic domains (writing).The electronics are all contained on a small board that detaches from the rest of the drive. Underneath the board are the connections for the motor that spins the platters, as well as highly-filtered vent hole that lets internal and external air pressure equalize.

Removing the cover from the drive reveals an extremely simple but very precise interior: the platters which are manufactured to amazing tolerances and are mirror-smooth and the arm that holds the read/write heads. It is controlled by the mechanism in the upper-left corner and is able to move the heads from the hub to the edge of the drive.

Data is stored on the surface of a platter in sectors and tracks. Tracks are concentric circles, and sectors are pie-shaped wedges on a track. A sector contains a fixed number of bytes. Either at the drive or the operation system level, sectors are often grouped together into clusters.

Hard disc has got some benefits – you can move to any point on the surface of the disc almost instantly; the information can be easily erased and rewritten, and it will “remember” the magnetic flux patterns stored onto the medium for many years.

IX. Say “true” or “false”. Correct the “false” sentences:

1. Removable storage appeared later than computer.

2. Removable storage has only one advantage.

3. Removable storage devices can be of three categories.

4. The most convenient is a floppy disc.

5. Hard disc consists of several floppy films.

6. File is a string of letters and numbers.

7. A hard disc is a sealed box controlled by electronics.

8. Data is stored in sectors and tracks.