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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
slide6
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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