External storage

This article is about external storage devices. For external storage in the context of data structures, see Reference (computer_science)#External_and_internal_storage.

In computing, external storage comprises devices that temporarily store information for transporting from computer to computer. Such devices are not permanently fixed inside a computer.

Semiconductor memories are not sufficient to provide the whole storage capacity required in computers. The major limitation in using semiconductor memories is the cost per bit of the stored information. So to fulfill the large storage requirements of computers, magnetic disks, optical disks are generally used.

Contents

Advantages of external storage

Types of external storage

Magnetic storage

Optical storage

Optical media are the media that use laser light technology for data storage and retrieval.

Optical storage devices

CD

CD stands for compact disk. The speed is much less than a hard disk. The storage capacity is 700 MB. Types of CDs include:

DVD

DVD stands for digital versatile disk. Its speed is much fast than CD but not as fast as hard disk. The standard DVD-5 technology has a storage capacity of 4.7 GB. The storage capacity changes with the standard used. Its storage capacity (4.7 GB) is much more higher than a CD(700 MB). It is achieved by a number of design changes.

Solid state storage

Flash memory is a solid state memory. It was invented in 1980s by Toshiba. A flash memory is a particular type of EEPROM (Electrically Erasable Programmable Read Only Memory). It is a no-volatile memory. It retains the stored information without requiring a power source.It is called as solid state memory because it has got on moving parts Flash memory is different from the regular EEPROM. In case of EEPROM data are erased one byte at a time which makes it extremely slower. On the other hand data stored in flash memory can be erased in blocks. That’s why it gets a name “flash memory” because the chip is organised in such a way that a block of memory cells can be erased at a single time or “flash”.

Advantages of flash memory

Disadvantages of flash memory

Flash memory devices

Other devices

Other external storage devices include:

Compare external storage which need not have a permanent connection to a computer: