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8.1 Hardware devices - Storage. Ranjit Bassi. Hard disk. The hard disk uses magnetic disk drives which allows rapid random access to large amount of data

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Hard disk
Hard disk

  • The hard disk uses magnetic disk drives which allows rapid random access to large amount of data

  • All disk drives use a thin circular platter made of non-ferrous metal or plastic and rotate it at up to 10,000 revolutions per minute beneath a read-write head that moves radially across the surface of the platter

  • The platter is coated with an emulsion of iron or cobalt oxide particles that act as tiny magnets

  • Binary data is recorded by aligning these tiny magnets in one direction to represent a binary 0 and in the opposite direction to represent a binary 1.

  • To read data stored on the hard disk, the read write head is moved to the desired track and waits for the relevant sector to pass beneath it.

  • In hard disk’s the greater amount of platters, the greater amount of storage capacity


Magnetic tape
Magnetic tape

  • This is a cheap alternative to store large quantities of data

  • Magnetic tape consists of a thin ribbon of plastic, the tape is coated on one side with a material that can be magnetised to record the bit patterns that represent the data

  • The cartridge which contains the tapes is completely sealed apart from an access door to put the tape into contact with the recording heads in the tape drive

  • A mechanism moves the tape between the supply and take-up reels

  • Storage capacities range from 10GB to 800GB and data transfer speeds range from 200KB to 20MB per second


Optical media
Optical media

  • Optical media disks (LaserVision) records the video image as a frequency modulated (FM) signal on a tight spiral track that makes 54,000 turns in covering a disc surface.

  • The turns of the spiral are 1.6 micrometres apart, corresponding to a track density of almost 16,000 tracks per inch(630 tracks per millimetre)

  • The FM signal is recorded by making pits or tranches in the disc’s surface; a pit is a physical depression

  • These discs have a very high storage capacity

  • Compact discs (CDs) store up to 74 minutes of very high quality audio on one surface of a 120mm plastic discs


Cd rom
CD-ROM

  • Success of CDs led to CD-ROM (Compact disks read only memory)

  • CD-ROMs had a high storage capacity of 600-700mb

  • They offer fast data access and portable and they are read only

  • Data is written onto the discs by using disc-mastering machinery that impresses pits into a continuous spiral track

  • The silvery data surface contains pits in a single track 3.5 miles long

  • The disc spins at 200-500 revolutions per minute depending on which radius is being read

  • A data bit is read by focusing a laser beam onto a point in the reflective metal layer where the pits are impressed


CD-R

  • CD-recordable discs that support WORM operation are available in the standard in the standard size of 120 mm

  • Also known as writable CDs

  • They can record about 600-700 MB of data

  • Any region of the disc can be written on but then it cannot be written on it again or altered

  • Data bits are recorded by burning a pit in a thin film of metal using a high-power laser


Cd rw
CD-RW

  • A CD-rewritable can be read and written on over and over again

  • CD-RW drives have a magnet and a laser

  • The write operation uses the magnet and laser but the read operation uses only the laser

  • To record or change data, the laser heats a precise spot on the disc to a temperature of 200 degrees

  • Capacity is similar to the CD-R


Dvd rom
DVD-ROM

  • Digital versatile disc or digital video disc is an optical standard that offers much greater storage capacity than CDs

  • On a DVD the minimum length of the pit is 0.4 micrometres

  • This lets the disc-mastering machinery squeeze the pits more closely together.

  • On a DVD the data track’s spiral spacing is 0.74 micrometres

  • DVD drives uses lasers with short wavelengths to read to very small pits

  • Reducing pit sizes increases the disc storage capacity to about 4.7 GB


Dvd r
DVD-R

  • DVD-R is a WORM format similar to CD-R

  • It replaces the layer of read only polycarbonate with an organic dye

  • DVD-R records data by burning spots in the dye to alter the amount of laser light reflected

  • The discs have a capacity of 4.7 GB

  • The life of these discs vary from 70 to 100 years


Dvd rw
DVD-RW

  • The DVD-RW format provides a rewritable optical disc with a typical capacity of 4.7 GB

  • These discs are made to be re-written up to 1000 times before a replacement is needed

  • A benefit of these discs compared to others are that when a writing error is made the whole disc is not ruined , it can still store data by erasing the faulty data

  • The recording layer in these discs are not organic dye but a special phase-change metal alloy

  • Data can be written, erased and rewritten


Dvd ram
DVD-RAM

  • DVD-RAM is a rewritable format that has built in error control and a defect management system

  • DVD-RAM is can be written and erased very easily

  • These discs store data in one spiral track and require special software for reading and writing

  • Storage capacities range from 2.58GB to 9.4GB


Blu ray disc
Blu-Ray Disc

  • This is a high density optical disc that stores digital information, including high definition video

  • Its name derives from the blue-violet laser used for reading and writing

  • It uses a wavelength of 405nm, this allows it to store more data

  • A single layer blue ray disc can store 25 GB and a dual layer Blu-ray disc can store up to 50GB

  • This disc offers very high transport speeds


Hd dvd
HD DVD

  • This type of DVD can store up to 30GB

  • This disc rivalled the Blu-ray disc but lost the race due to the backing of Hollywood studios causing HD DVD’s demise

  • They are written and erased like a normal DVD using a red laser as normal


Solid state memory
Solid state Memory

  • NAND-type flash memory is a type of EEPROM which supports erasure of an individual block of memory cells

  • To alter the contents of a particular memory location, it copies the entire block into an off-chip buffer memory, erases the block, then rewrites the data back into the same block, making the necessary alteration to the relevant memory location

  • It requires a dedicated microprocessor with RAM buffer and this is included in a USB flash memory drive.

  • It can also be used as a music coded to turn a flash drive into an MP3 player


Usb flash drive
USB Flash Drive

  • A USB flash drive or memory stick is a NAND-type flash-memory device plus a USB interface.

  • A flash drive consists of a small printed circuit board typically in a plastic or metal casing, making the drive sturdy enough to be carried about in a pocket

  • Only the USB connector protrudes from this from this protection and it is usually covered by a removable cap

  • A NAND-type flash memory chip is mounted on the printed circuit board

  • Flash drives are relatively dense form of storage; even the cheapest flash drive can store all the data on dozens of floppy discs

  • Storage capacities range from 64MB to 32GB

  • Manufacturers are starting to ship laptops with flash memory secondary storage instead of magnetic hard disk storage

  • This is due to low power consumption and faster booting of the operating system


Memory card
Memory Card

  • A memory card is a solid state flash memory device used for data-storage in digital camera

  • These cards offer high capability, power-free storage, a small form factor and rugged environmental specifications

  • Storage capacities range from 128MB to 4GB


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