USB flash drive
Internals of a typical flash drive:
2USB mass storage controller device
4Flash memory chip
8Space for second flash memory chip
USB flash drives are NAND-type flash memory data storage devices integrated with a USB interface. They are typically small, lightweight, removable and rewritable. Memory capacity typically ranges from 128 megabytes up to 64 gigabytes , USB flash drives have several advantages over other portable storage devices, particularly the floppy disk. They are more compact, generally faster, hold more data, and are considered more reliable than floppy disks. These types of drives use the USB mass storage standard, supported natively by modern operating systems such as Linux, Mac OS X, and Windows XP. A flash drive consists of a small printed circuit board encased in a robust plastic or metal casing, making the drive sturdy enough to be carried about in a pocket, as a keyfob, or on a lanyard. Only the USB connector protrudes from this protection, and is usually covered by a removable cap. Most flash drives use a standard type-A USB connection allowing them to be connected directly to a port on a personal computer.
The flash drive was first invented in 1998 by Dov Moran, President and CEO of M-Systems Flash Pioneers (Israel).The first flash drives were made by M-Systems and distributed in Europe under the "disgo" brand in sizes of 8 MB, 16 MB, 32 MB, and 64 MB. These were marketed as "a true floppy-killer", and this design was continued up to 256 MB. Asian manufacturers soon started making their own flash drives that were cheaper than the Disgo series.Modern flash drives have USB 2.0 connectivity. However, they do not currently use the full 480 Mbit/s the specification supports due to technical limitations inherent in NAND flash.
Compact Disc (CD) is an optical disc used to store digital data, originally developed for storing digital audio . Standard compact discs have a diameter of 120 mm or 80 mm. The 120 mm discs can hold approximately 80 minutes of audio. The 80 mm discs, sometimes used for CD singles, hold approximately 20 minutes of audio. Compact disc technology was later adapted for use as a data storage device , known as a CD-ROM , and to include record-once and re-writable media (CD-R and CD-RW) . Compact discs are made from a 1.2 mm thick disc of very pure polycarbonate plastic . A thin layer of Super Purity Aluminium .is applied to the surface to make it reflective, which is protected by a film of lacquer .
In 1979 Philips and Sony decided to join forces, setting up a joint task force of engineers whose mission was to design the new digital audio disc.The Compact Disc Story, told by a former member of the taskforce, gives background information on the many technical decisions made, including the choice of the sampling frequency, playing time, and disc diameter. The Compact Disc reached the market in late 1982 in Asia. This event is often seen as the "Big Bang" of the digital audio revolution. The design of the CD was originally conceived as an evolution of the gramophone record, rather than primarily as a data storage medium.In 1998 CD disc,and 1990 CD-Recordable were introduced, also developed by Sony and Philips.
DVD (also known as "Digital Versatile Disc" or "Digital Video Disc") is an optical disc storage media format that can be used for data storage, including movies with high video and sound quality. DVDs resemble compact discs as their physical dimensions are the same (120 mm (4.72 inches) or occasionally 80 mm (3.15 inches) in diameter) but they are encoded in a different format and at a much higher density.
A floppy disk is a data storage device that is composed of a disk of thin, flexible ("floppy") magnetic storage medium encased in a square or rectangular plastic shell. Floppy disks are read and written by a floppy disk drive or FDD.
DVD disc capacity
Single layer capacity (DVD-5)Dual/Double layer capacity (DVD-9)
12 cm, single sided4.74.388.57.92
12 cm, double sided9.48.751715.8
8 cm, single sided1.41.302.62.42
8 cm, double sided2.82.615.24.84