Secondary Storage Devices
1. Secondary Storage Devices
Secondary storage devices cannot be classified under input or output devices. These devices are used to store data for later use.
Secondary storage devices can be categorized in 3 main groups:
1. Magnetic
2. Optical
3. Electronic
1. Magnetic Storage - Magnetic storage devices store the data on a magnetic layer. Examples of such devices are:
a. Floppy Disk
b. Hard Disk
c. Magnetic Tape
The technology used is very simple to understand. The magnetic layer is magnetized when there is a binary 1 and left un-magnetized when there is a binary 0.
Floppy Disk - Floppy disks store small amount of data typically not larger than 1.44MB. These small diskettes are used mainly to transport small files from one computer to another. The construction of the floppy is basically a plastic disk coated with magnetic material, enclosed in a PVC jacket to protect the magnetic material. In order to write data to a floppy this must be first formatted. This procedure involves the creation of sectors and tracks. On the diskette, data is recorded on closed concentric rings (tracks). Each track is divided into sectors. These are invisible wedged-shaped sections used by the computer for storage reference purposes.
Hard Disks - As the name implies, hard disks are built with metal or glass platters covered with a substance that allows data to be held in the form of magnetised spots. Today hard disks are composed of more than one disk (also named as platter), which are stacked on each other. This technology gives the possibility of having large storage capacity. Typically computer systems today have an 160GB (or more) hard disk capacity.
Magnetic Tape - This type of storage media is used in large computers where large amounts of data are stored. The tape is made up of a thin plastic tape having horizontal running tracks and vertical frames. Magnetic tape is ideally suited to store a list of records whose sequential order is sorted for later processing. Payroll systems and record updating is ideal for tape. A sorted tape can be used to issue pay cheques, update a list of customers etc.
2. Optical Storage -
The CD-ROM Disk - CD-ROM stands for Compact Disk - Read Only Memory. This is an optical disk where information is stored at the time of manufacturing. Examples of CD-ROM are Music CD�s and software that one buys from computer shops such as games. Optical disks write data with a high power laser beam, which records data by burning tiny pits onto the surface of the disk. In order to read data, a low power laser beam reads data by reflecting smooth areas, which are interpreted as 1 bits, and not reflecting pitted areas which are interpreted as 0 bits. The typical storage capacity of a CD-ROM is 650Mb, which makes them a very versatile data storage media when it comes to store data for short and long term periods of time.
CD-R - CR-R which stands for Compact Disk- Recordable is a CD format that allows users to use a CD-R drive to write data, only once, onto a specially manufactured disk that can then be read by a standard CD-Rom drive.
CD-RW - CD-RW stands for Compact Disk - Rewritable. This type of media allows users to copy and erase data. Thus, this disk can be used over and over again.
DVD-Rom - DVD-Rom stands for Digital Video Disk or Digital Versatile Disk. This optical disk looks like a normal CD but in fact, it can store much more data than a CD
3. Electronic Storage - Electronic memory is the latest technology in secondary storage media. This is also referred to as Flash memory. Flash memory is non-volatile solid-state computer memory storage that can be electrically erased and reprogrammed. It is a technology that is primarily used in memory cards and USB flash drives for general storage and transfer of data between computers and other digital products. It is a specific type of EEPROM (Electrically Erasable Programmable Read-Only Memory). This type of memory media has no mechanical moving parts and thus it offers some advantages when compared to the other type of media.
Advantages: Very small , Does not consume a lot of energy in order to function , Noiseless , Limited heat emission , Portable
Disadvantages: Limited amount of memory capacity when compared to the other type of media (Currently big advancements are being made and the maximum capacity of this media is 60GB).
Because of their small size and big capacity, electronic memory is suitable to be used in portable devices. Today electronic memory is being used in Digital cameras, Mp3 Players, PDAs, Mobile phones and Laptops.
Backing Storage Device, Media and Access Type -
|
DEVICE |
MEDIA |
TYPE |
ACCESS |
|
Cassette Tape Drive |
Cassette Tape |
Magnetic |
Serial |
|
Reel to Reel Tape Drive |
Reel Tape |
Magnetic |
Serial |
|
Floppy Disk Drive |
Floppy Disk |
Magnetic |
Direct |
|
Hard Disk Drive |
Hard Disk |
Magnetic |
Direct |
|
Zip Drive |
Zip Disk |
Magnetic |
Direct |
|
CD-Rom Drive |
CD-Rom |
Optical |
Direct |
|
WORM Drive |
WORM |
Optical |
Direct |
|
CD-R, CD-RW |
CD-R, CD-RW |
Optical |
Direct |
|
DVD Drive |
DVD |
Optical |
Direct |
|
Flash Memory Unit |
Flash Memory Card |
Electronic |
Direct |
