Digital Mass Storage Technologies and Devices

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Digital Mass Storage Technologies and Devices

• Introduction
• Early digital storage technology
• Todays technologies
• How they work
• Future technologies
• Summary

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IntroductionThe Demand for Data Storage

• Paper punch cards were first to store computing
  data.
• It is estimated that 250 megabytes of information
  is produced every year for each man, woman, and
  child (1 to 2 exabytes in total.)
• Printed documents make up only .003 of this
  total.

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IntroductionStorage for PCs

• Rapid growth in late 80s/early 90s helped fuel
  demand for cheap storage devices.
• Transfer speeds, capacities, costs, and
  convenience were main factors.
• Tape drives were slow and limited, floppy drives
  were quick to replace them.
• Hard drives became standard components but were
  not portable.

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Early Storage Technologies

• The first hard drive.
• Introduction of the personal computer.
• Floppy drives.
• Bernoulli disk drives.
• Cheaper, faster, and smaller drives with higher
  storage capacities.

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The First Hard Drive

• Punch cards were used until the 1950s. First
  introduced in the early 1800s for use with silk
  weaving looms.
• Magnetic tape replaced them.
• In 1957, IBM developed the first hard drive as
  part of their RAMAC system. It required 50
  24-inch disks to store 5 megabytes of data and
  cost 35,000/year to lease.

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Introduction of the PC

• Hard drives were first used in mainframe and
  minicomputer systems, filling an entire
  air-conditioned room.
• PCs first used magnetic tape for storage
  (reel-to-reel and later cassettes.)
• 5.25-inch floppy drives became popular in the
  early 80s, holding 360KB of data.
• Hard drives got smaller, more affordable, and
  more popular, storing between 5 and 20MB of data.

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Floppy Drives

• Operate much like a hard drive but uses removable
  disks.
• Slower and have smaller storage capacity than a
  hard drive (360KB to 1.2MB).
• Rigid 3.5-inch floppy later introduced and able
  to store nearly 2MB per disk.

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Bernoulli Disk Drives

• Special type of floppy drive that was faster and
  held more data.
• Disks were flexible and removable.
• Read/write head never touched surface of disk,
  similar to a hard drive.
• No longer being produced.

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Falling Prices, Smaller Drives, Higher Capacities

• Prices for hard drives have declined rapidly
  since the 1980s.
• A 20MB hard drive in 1985 cost around 1,000, or
  50/megabyte.
• By 2000 the price was 10/gigabyte.
• Expected to drop to 1/gigabyte by 2005.
• 200GB drives currently available for under 300
  (1.50/gigabyte).
• Physical size of drives continues to shrink.

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IBM Hard Drive Evolution
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Todays Storage Technologies

• Magnetic storage
• Optical storage
• Magneto-optical (MO)
• Solid state storage

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Magnetic StorageCassette Tape

• Slow write and retrieval speeds, but inexpensive
  and portable.
• Digital Audio Tape (DAT) able to store from 2 to
  24GB of data on a tape about the size of a credit
  card.
• Digital Linear Tape (DLT) is generally faster and
  able to hold 200GB or more per cassette.
• Primary use is data backup or archival,
  especially for servers.

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Magnetic StorageHard Drives

• Most common storage device in use today.
• Low cost, fast response, reliable, small.
• Demand continues to grow with 144.9 million
  drives shipped in 1998 and 252.9 million expected
  in 2002.

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Magnetic StorageFloppy Drives

• Havent changed much but are still popular.
• Current drives store nearly 2MB on a single
  3.5-inch disk.
• Very inexpensive, but also very slow.
• Not the most reliable type of storage
  (susceptible to magnetic fields, wear, damage,
  etc.)

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Magnetic StorageZip Jaz Drives

• Created by Iomega corporation.
• Portable drives able to store more information
  than a standard floppy disk.
• Zip drives can store between 100 and 750MB of
  data, depending on model.
• Jaz drives can store up to 2GB, but are no longer
  being produced.
• Have been very popular, but CD-RW drives now
  provide similar capabilities at comparable costs.

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Optical StorageCD-ROM and DVD-ROM

• Technology dates back to 12-inch laserdisc
  developed by Philips in the 1970s.
• CD-ROM is capable of storing around 650MB of
  data.
• DVD-ROM is capable of storing nearly 16GB (double
  sided/double layer.)
• DVDs are expected to replace many older
  technologies including CDs, VHS, laserdiscs.
• ROM (read-only memory) means data is written once
  and cannot be changed.
• Very cheap to produce and distribute.

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Optical StorageCD-R

• Short for Compact Disc-Recordable.
• Known as Write Once Read Many (WORM), these discs
  can be written to only once. The data is then
  permanent like a CD-ROM.
• Extremely cheap (pennies per disc.)

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Optical StorageCD-RW

• Short for Compact Disc-ReWritable.
• These discs can be written to multiple timesthe
  data is not permanent.
• Prices for CD-RW drives and discs have fallen
  considerably in the past few years.
• An ideal solution for portable data storage.
• CD-RW discs can usually be read by CD-ROM drives.

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Optical StorageDVD-R and DVDR

• Two different and incompatible technologies.
• Both allow data to be written to a DVD only once,
  similar to CD-R.
• Capacity for both is 4.7GB per disc.

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Optical StorageDVD-RW and DVDRW

• Two different and incompatible technologies.
• Both allow data to be written to a DVD multiple
  times, similar to CD-RW.
• Discs can be rewritten about 1,000 times and can
  store 4.7GB of data.

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Optical StorageDVD-RAM

• Yet another technology incompatible with DVD-RW
  and DVDRW.
• Targeted for computer platforms.
• Faster data access times.
• Better defect management.
• Discs can be rewritten 100,000 times and will
  last at least 30 years.
• Ideal for data backup and archival (improvement
  over tape backup.)

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Magneto-Optical Storage

• Combines magnetic disk technologies with laser
  technology.
• Can be read and written to over one million
  times.
• Portable.
• Capacity is 2GB or more per disk.
• Faster than floppies and CDs, but slower than
  hard drives.

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Solid State Devices

• Known as flash memory.
• No moving partsinternal transistors provide
  storage.
• Similar to EEPROM but much faster.
• Can store up to 1GB of data in a very small,
  portable package (4GB modules are coming soon.)
• Used in digital cameras, media players, and other
  small devices.

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How Do They Work?

• Cassette tapes
• Hard disk drives
• Floppy drives
• Zip and Jaz drives
• CD-ROM and DVD-ROM
• CD-R
• CD-RW
• DVD-R and DVDR
• DVD-RW and DVDRW
• Magneto-optical
• Solid state devices

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Cassette Tapes

• Works similarly to an audio cassette.
• Data is read and written using a read/write head
  that makes contact with the magnetic tape.
• Data is stored digitally.
• Uses helical scan technology (first used in VCRs)
  where head spins and writes data in diagonal
  tracks.

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Hard Disk Drives

• Operates like a record player.
• Several aluminum-alloy platters coated with a
  magnetic material.
• Small space in-between platters and data stored
  on both sides.
• Platters constantly spinning at 7200 RPM or
  faster.
• Actuator arms contain read/write heads.
• Data arranged in tracks on platter and divided by
  sectors.

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Hard Disk DrivesPlatter Surface Diagram
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Hard Disk Drives

• Information written to outer tracks first.
• All platters used as one large platter.
• Data can become fragmented, reducing performance.
  Software utilities can defragment a drive.
• The read/write head flies just a few microinches
  above the surface of the platter on a cushion of
  air.

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Hard Disk DrivesRead/Write Head
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Hard Disk Drives

• Heads touch down in a safe spot when drive is
  powered off.
• A head crash happens when the head collides
  with the platter surface. Can result in data
  loss or destruction of the drive.
• Most drives can sustain shocks in the range of 60
  to 100Gs while in operation. Even higher when
  turned off.

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Floppy Drives

• Work essentially the same as a hard drive.
• Only contain one platter.
• Disk stops spinning when not in use.
• Disk spins at lower RPMs since head makes
  physical contact with the surface.
• More vulnerable to wear and environmental effects.

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Zip Jaz Drives

• Very similar to floppy drives.
• Disks are larger than floppy disks and can store
  more information.
• Multiple interfaces available parallel, USB,
  floppy, etc.

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CD-ROM

• Works by reading bumps and low spots, or pits and
  lands on a disc with a laser.
• Discs contain three layers plastic, aluminum,
  and acrylic.
• Aluminum layer reflects laser light, a detector
  can determine the difference between a pit and
  land.

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DVD-ROM

• Works same as CD-ROM, but bumps are smaller and
  packed closer together.
• Contains less error correction information
  (better error correction algorithm than CDs.)
• Supports double layer storage, effectively
  doubling the storage area.
• Drive does not spin at a constant speed which
  allows a constant data rate stream.

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CD-R

• Contains an extra greenish-dye layer that can be
  modified with a write laser.
• During the write process, a laser heats up the
  dye layer and changes its transparency, producing
  a non-reflective area.

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CD-RW

• Also contains an extra dye layer, but the dye can
  change states multiple times using phase-change
  technology.
• Heated to one temperature, the material cools to
  a transparent state.
• Heated to another temperature, it cools to a
  cloudy state.

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CD-RWDisc Layers
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CD-RWRecording Process
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DVD-R and DVDR

• Similar to CD-R, these discs contain an extra dye
  layer that can be written to one time.

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DVD-RW and DVDRW

• Both contain an extra dye layer and use
  phase-change technology in the same way CD-RW
  works.
• DVD-RW uses groove recording with address info on
  land areas for synchronization at write time.
• DVDRW uses a high-frequency wobbled groove that
  allows it to eliminate linking sectors.
• Two technologies backed by two different sets of
  companies.
• Multi-mode drives capable of supporting both are
  now being produced.

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DVD-RAM

• Uses phase-change dual (PD) technology with some
  magneto-optic (MO) features.
• Data layers are made of very thin metal film that
  can change state over 100,000 times.

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Magneto-Optical

• MO drives combine magnetic and optical
  technologies.
• Early drives used a read/write magnetic head to
  record data while a laser heated up magnetic
  material allowing it to change polarity. This
  was a slow process.
• In 1997, LIMDOW was introduced and did away with
  the read/write head. Two magnets were build into
  the disc. A laser is used to heat the recording
  layer. At one temperature, it takes the polarity
  of the first magnetic. At another, the other.

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Magneto-Optical

• A laser is used to read information off the disk
  using the Kerr Effect, where the polarity of the
  reflected light is altered depending on the
  orientation of the magnetic particles.
• Speeds are nearly as fast as hard drives.

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Magneto-OpticalKerr Effect
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Solid State Storage

• Uses a chip containing a grid with a
  two-transistor cell at each intersecting point on
  the grid.
• Cell value is changed using electrical processes.
• Faster than EEPROM because entire blocks can be
  erased at one time.
• Two devices in use CompactFlash and SmartMedia.

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What about the Future?

• Optical super density
• Multilevel recording
• Blu-ray disc
• Fluorescent disc technology
• Holographic memory
• Probe storage

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Optical Super Density

• High capacity (40GB or more) removable MO drive.
• Data transfer rates comparable to hard drives.
• Lower cost per MB than other optical and tape
  products.
• Targeted for long term storage needs10 million
  overwrites and 50-year shelf life.

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Multilevel Recording

• CD that uses gray-scale encoding, with 3 bits per
  spot giving eight shades of gray.
• Disc surface appears as a continuous blending of
  light to dark shading, versus the traditional
  dark or bright (pits and lands) spots.
• Up to 2GB per disc.
• Existing CD and DVD players only need IC upgrade
  to read discs.

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Blu-ray Disc

• CD capable of storing 27GB.
• Uses blue laser as opposed to current red laser.
• Blue laser can focus on smaller area, allowing
  more information to be stored in a given area.

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Fluorescent Disc Technology

• Increases number of disc layers.
• Recording layers contain a transparent organic
  substance whose fluorescence can be triggered by
  a laser.
• Able to read off multiple layers at one time.
• Potential to store 1TB in a 16cm2 area using 50
  layers.
• First devices likely to store only 5-100GB.

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Holographic Memory

• Uses multiple layers of 3D holograms.
• Potential storage of 1TB in a sugar-cube-sized
  crystal.
• Very fast retrieval speeds.
• Different layers are accessed by changing angle
  of laser beam.
• Already being used in fingerprint identification
  systems.

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Holographic Memory
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Holographic Memory
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Probe Storage

• Return of the punch card!
• Based on atomic force microscopy.
• One trillion bits per square inch, more than 20
  times denser than todays drives.
• 1,024 probes were used to read, write, and erase
  data on a plastic medium.
• Competing technology uses phase-change.

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Probe Storage
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Summary

• Demand continues to grow.
• Cost per megabyte is decreasing.
• DVDs replacing older technologies.
• Convenience, cost, acceptance, and capacity will
  drive new products.
• Several new technologies on the horizon,
  providing reduced sizes with increased capacities
  and data transfer rates.

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