Working Principle of different types of tape drives

Tracy Pettigrue
Tracy Pettigrue
Oct 1, 2009
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A tape drive, also known as a streamer, is a data storage device that reads and writes data stored on a magnetic tape or a punched tape.


Instead of allowing random access to data as hard disk drives do, tape drives only allow for sequential access of data. A tape drive must spend a considerable amount of time winding tape between reels to read any one particular piece of data. As a result, tape drives have very slow average seek times. Despite the slow seek time, tapes drives can stream data to tape very quickly.


The read/write heads in a tape drive are U-shaped pieces of conductive material, with the ends of the U situated directly above (or next to) the surface of the actual data storage medium. The U-shaped head is wrapped with coils or windings of conductive wire, through which an electric current can flow. When the drive logic passes a current through these coils, it generates a magnetic field in the drive head. Reversing the polarity of the electric current causes the polarity of the generated field to change also. In essence, the heads are electromagnets whose voltage can be switched in polarity very quickly.


Advantages of Tape Drives:


1. Since the tape is extremely thin (a few microns) and is wound upon itself, it offers extremely high volumetric density of storage.

2. Tape is relatively inexpensive and may be removed from the drive.

3. Performance tape drives are high-end tape products used predominantly for large computer systems.

4. Compact tape drives are small form factor drives, which are typically used for disk backup on personal computers as well as on a network.

5. Tape backup drives are necessary if you need to restore from previously made backup tapes.

6. Tape backup drives are a good choice as an easy media rotation method for preserving multiple full-system backups.

7. Tape Drives has its use in keeping large amount of data safe.


Different types of CD formats available:


There is basically two types of CD formats available:


1. Live File System and,


2. Mastered



Description of the CD Formats:


Live File System:


1. This format works like a USB flash drive or floppy disk, so that files can br copied to disc immediately without having to burn them.

2. This format is convenient if a disc is required to be kept in a the burn drive and copy files whenever the need arises.

3. This format is only compatible with Windows XP and later versions of Windows.


Mastered System:


1. This system do not copy files immediately. The entire collection of files is needed to be selected. that is needed to be copied to the disc, and then burn them all at once.

2. This format is convenient if a large collection of files is required to be burned, such as a music CD.

3. This format is compatible with older computers and devices such as CD players and DVD players.


Latest Development of CD drives and storage media:




AVCHD (Advanced Video Codec High Definition) is a new high definition recording format introduced by Sony and Panasonic. It can use various storage media, including 8 cm (3") recordable DVD discs, as well as hard disk, and SD and Memory Stick Pro memory cards, and is being positioned to compete with handheld video camera recording formats like HDV and MiniDV. Among the touted advantages of AVCHD over MiniDV tapes is true random access, since time-based seeking on AVCHD does not involve a fast-forward/rewind operation as it would on tape-based formats such as miniDV.




The name Blu-ray Disc is derived from the blue-violet laser used to read and write this type of disc. Because of this shorter wavelength (405 nm), substantially more data can be stored on a Blu-ray Disc than on the DVD format, which uses a red, 650 nm laser. Blu-ray Disc can store 25 GB on each layer. About 9 hours of high-definition (HD) video can be stored on a 50 GB disc. About 23 hours of standard-definition (SD) video can be stored on a 50 GB disc. On average, a single-layer disc can hold a High Definition feature of 135 minutes using MPEG-2, with additional room for 2 hours of bonus material in standard definition quality. A dual layer disc will extend this number up to 3 hours in HD quality and 9 hours of SD bonus material.


Digital MultiLayer Disc:


Digital Multilayer Disk (DMD) is an optical disc format developed by D Data Inc. It is based on the Fluorescent Multilayer Disc, which was created by Constellation 3D. This format can store between 22 and 32 GB of binary information. It is based on the red laser technology, so DMD discs and players can be easily made in the existing plants with little modifications. Discs are composed of multiple data layers joined by a fluorescent material. Unlike actual DVDs and CDs, DMD do not have metallic layers, so they are nearly transparent. Each one is coated with proprietary chemical compositions, and those chemicals react when the red laser shines on a particular layer. That chemical reaction generates a signal, which is then read by the disc reader. HD-DMD can dramatically increase the storage capacity of a single standard disc.


Enhanced Versatile Disc:


The Enhanced Versatile Disc (EVD) is an optical medium-based digital audio/video format, developed to provide a means for playing HDTV content using existing optical media. It uses an optical storage medium in CD size (120 mm) that is physically a DVD disc with the same UDF file system.


Fluorescent Multilayer Disc:


Fluorescent Multilayer Disc (FMD), is an optical disc format developed by Constellation that uses fluorescent, rather than reflective materials to store data. However, the use of fluorescence allows FMDs to have up to 100 layers. These extra layers allow FMDs to have capacities up to a terabytes, while maintaining the same physical size of traditional optical discs. The pits in an FMD are filled with fluorescent material. When coherent light from the lasers strikes a pit the material glows, giving off incoherent light of a different wavelength. Since FMDs are clear, this light is able to travel through many layers unimpeded. The clear discs, combined with the ability to filter out laser light yield a much greater signal-to-noise ratio than reflective media. This is what allows FMDs to have many layers. The main limitation on the number of layers in a FMD is the overall thickness of the disc.


Holographic Versatile Disc


Holographic Versatile Disc (HVD) is an optical disc technology still in the research stage which would hold up to 3.9 terabytes(TB) of information. It employs a technique known as collinear holography, whereby two lasers, one red and one blue-green, are collimated in a single beam. The blue-green laser reads data encoded as laser interference fringes from a holographic layer near the top of the disc while the red laser is used as the reference beam and to read servo information from a regular CD-style aluminum layer near the bottom. Servo information is used to monitor the position of the read head over the disc, similar to the head, track, and sector information on a conventional hard disk drive. On a CD or DVD this servo information is interspersed amongst the data.


Tapestry Media


Tapestry Media is a digital optical disc about the size of a DVD with a capacity of 300GB. The Tapestry system uses light from a single laser split into two beams: the signal beam and the reference beam. The hologram is formed where these two beams intersect in the recording medium. The process for encoding data onto the signal beam is accomplished by a device called a spatial light modulator, which translates the electronic data of 0s and 1s into an optical "checkerboard" pattern of light and dark pixels. The data is arranged in an array or "page" of around a million bits. At the point of intersection of the reference beam and the signal beam, the hologram is recorded in the light sensitive storage medium. A chemical reaction occurs in the medium when the bright elements of the signal beam intersect the reference beam, causing the hologram. By varying the reference beam angle, wavelength or media position many different holograms can be recorded in the same volume of material.


Ultra Density Optical


Ultra Density Optical (UDO) is a next-generation optical disc format designed for high-density storage of high-definition video and data. An Ultra Density Optical disc or UDO is a 5.25" ISO cartridge optical disc encased in a dust-proof caddy which can store up to 30 GB of data. Utilising a design based on a Magneto-optical disc, but uses Phase Change technology combined with a blue violet laser, a UDO disc can store substantially more data than a magneto-optical disc or MO, because of the shorter wavelength (405 nm) of the blue-violet laser employed. MOs use a 650-nm-wavelength red laser. Because its beam width is shorter when burning to a disc than a red-laser for MO, a blue-violet laser allows more information to be stored digitally in the same amount of space.


Protein-Coated Disc


Protein-Coated Disc (PCD) is a theoretical optical disc technology currently being developed by Professor V Renugopalkrishnan of Havard Medial school. PCD would greatly increase storage over Holographic Versatile Disc optical disc systems. It involves coating a normal DVD with a special light-sensitive protein made from a genetically altered microbe, which would in principle allow storage of up to 50 Terabytes on one disc. The light-activated protein is found in the membrane of a salt marsh microbe Halobacterium salinarum and is also known as bacteriorhodopsin(bR). It captures and stores sunlight to convert it to chemical energy. When light shines on bR, it is converted to a series of intermediate molecules each with a unique shape and colour before returning to its "ground state". Since the intermediates generally only last for hours or days, Professor V Prof Michael G and his colleagues modified the DNA that produces bR protein to produce an intermediate that lasts for more than several years. They also engineered the bR protein to make its intermediates more stable at the high temperatures generated by storing terabytes of data. The information in such discs would be highly dense, due to being stored in proteins that are only a few nanometres across.

Author's note: Hope it helps junior CSE students
Keywords: Tape Drives, Protein-Coated Disc, Tapestry Media, Holographic Versatile Disc, Fluorescent Multilayer Disc, Enhanced Versatile Disc, Digital MultiLayer Disc, BLUE RAY, AVCHD,CD formats

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