Storage and Multimedia

1
Chapter 6

• Storage and Multimedia

2
Secondary Storage

• Secondary storage is storage is separate from the
  computer itself
• Benefits
• Space-generally can store much more than primary
  storage
• Reliability-data is safe because storage is
  relatively safe
• Convenience-can locate data quickly
• Economy-less expensive than the non-computerized
  options

3
Magnetic Disk Storage

• Magnetic media based on a technology where data
  is represented as a magnetized spot on the
  spinning disk (magnetized spot 1,
  non-magnetized0)
• Magnetic spots are transmitted to electrical
  impulses when the data I being read
• Electrical impulses from the processor are
  converted to magnetic spots when writing takes
  place

4
Floppy Disk

• Made from flexible mylar coated with iron oxide
• Most computers today have floppy disks that hold
  1.44mb and are 3.5 inches
• Has protection of the hard disk
• Small size makes it very portable
• Sometimes used to back up files
• New disk formats include
• HIFD (200 MB)
• SuperDisk (120 and 240MB)
• Zip Drive-largest market share can store up to
  750MB

5
Hard Disks

• A rigid platter coated with magnetic oxide that
  can be magnetized to represent data
• Several platters can be assembled in to a disk
  pack
• Each disk can be written to on the top and
  bottom, although many times to top of the top
  disk and the bottom of the bottom disk are left
  blank

6
Hard Drives

• The hard drive actually refers to the device that
  enables reading and writing to the disk
• A computer can have one to hundreds of disk
  drives
• In the disk pack, all disks rotate at the same
  time even though only one is being read/written
  to

7
How the Hard Drive Works

• The access arm, which contains the read/write
  head moves in to position over the magnetic media
• The read/write access sits 1 millionth of an inch
  above the media but does not touch the media
• If it does, data is destroyed in a head crash
• Read/write heads usually travel in pairs, one
  pointing up and one pointing down

8
Hard drive storage capacity

• Storage is growing and getting cheaper
• Current hard drives for PCs are available now in
  the 250GB range (approx 300) but most common
  still in the 120GB range (150ish)
• External drives (more expensive) sit outside the
  computer case whereas internal drives are
  generally installed inside the case
• Removable hard drives such as the Jaz drive are
  not as common due to expense

9
RAID

• Redundant Array of Independent disks
• Used to protect data
• Two types
• RAID level 0-uses data striping which spreads
  data from a single file across several drives
  allows simultaneous read/write which improves
  performance
• RAID level 1- also called disk mirroring because
  it makes a mirror image of the data on a second
  drive

10
How Data is Organized

• Track
• Refers to the circular portion of the disk
• Number of tracks depends on the size of the disk
  (160 for floppies, 1000s on hard drives)
• Sector
• Tracks are divided into sectors of a fixed number
  of bytes, usually 512
• Generally, data is located according to its
  surface (top or bottom), its track, then its
  sector on that track

11
Zone Recording

• To increase storage, disks are divided into zones
  and outer zones have more sectors assigned per
  track
• However, note that data stored in outer tracks is
  less efficient because of the circular nature of
  the disk

12
Clusters

• Groupings of adjacent sectors that are treated as
  a unit of storage by the OS, generally 2 to 8
  sectors
• Each file is stored in an integral number of
  clusters
• Example Our OS clusters 2 sectors as a cluster
  and our file is 1025 bytes. How many clusters
  will our file require for storage?

13
Answer.

• Our file will required 2 clusters
• One cluster holds 2 sectors which generally are
  512 bytes a piece (1024 total)
• Our file is 1025 and the data is stored in
  integral numbers of clusters, so the OS will
  allocate the second cluster just to accommodate
  that last byte

14
Cylinders

• Defined as the track on each surface beneath the
  read/write head at a given position of the
  read/write arms
• What this really means is what is under the
  read/write head on the top of the disk and what
  is under the read write arm on the bottom of the
  disk
• Data is stored in cylinders to allow for vertical
  access to data which requires less physical
  movement (and time!) of the read write arm

15
Disk Access Speed

• Access time is the time needed to access data on
  the disk, generally measured in milliseconds
• Three factors
• Seek time-time to get the arm into place over the
  track
• Head Switching-Activation of either the top or
  bottom head since only one can read or write at a
  time
• Rotational Delay-data must spin under the
  read/write head

16
Data transfer

• After data is accessed, data transfer is either
  from memory to disk (write) or from disk to
  memory(read).
• Data transfer rate, another measure of
  performance, is measured in MB/sec and measures
  how fast data is transferred once found

17
Disk Cache

• To improve performance, hard drive reads data
  around what it was told to read and stores it in
  disk cache.
• Next time the Control Unit tells it to read data,
  it checks this cache first in hopes of not having
  to perfrom another physical read
• Speeds up performance if its in cache

18
Optical Disk Storage

• A fancy way to say CDs and DVDs
• Optical disks work like this
• When writing, laser hits metal and makes little
  dots
• Then to read, laser hits the disk and the light
  reflects back from the pits
• Disks are categorized by their read/write nature
• Read only says it all, you can only read
• Write once, read many also called WORM means it
  can be written once, and then read til the cows
  come home
• Magneto-optical-can be rewritten and read many
  times

19
Compact Disks

• Compact Disks generally store 700MB
• CD-ROM versus a regular old CD means Compact Disk
  Read Only Memoryits for a computer and it can
  only be read
• CD-R-write once and can be read by any CD drive
• CD-RW-read write many times may not work on all
  CD drives

20
DVD ROM

• Digital Versatile Disk
• A CD on steroids, has same functionality as its
  CD counterpart
• Holds up tp 4.7 GB
• Uses shorter laser to read more densely packed
  dots
• Disks have two layers per side, a clear and opaque

21
Writing DVDs

• Things are a little cloudier when writing DVDs
• Standards are not solid as technology emerges
• DVD-RAM-writable
• DVD-R -writable
• DVDR writable
• DVD-RW-rewritable
• DVDRW-rewritable
• New standards such as Blu-Ray use different laser
  for even greater storage
• More info at http//www.dvdplusrw.org/faq/faq_gene
  ral.html1

22
Multinedia

• Software that presents data in many different
  media such as images, sound, and video
• Made possible by larger storage media such as the
  CDROM
• What you need for the multimedia experience
• CD or DVD Drive
• Sound card and speakers
• Other options include high speed hard drives,
  high resolution graphics cards, and software such
  as an MPEG player (video format stands for Motion
  Picture Experts Group)

23
Some examples of multimedia

• Many educational software titles today are
  multimedia applications
• Electronic versions of journals and books
• Business applications including training
  materials, database applications, marketing
  software
• Educational uses unlimited to increase the
  education experience for students through
  different media

24
Magnetic Tape Storage

• Tapes that look similar to standard cassette
  tapes with a magnetic coating
• Come in different sizes with different storage
  capacities
• Capacity is expressed in terms of density CPI
  (characters per inch) and BPI (bytes per inch)
• Optical disks have reduced the need for tape and
  they are mainly used for inexpensive, qucik
  backup options

25
Backup Systems

• Backup system is defined as storing important
  data in another location in case of failure
• Can range from copying your term paper to a
  floppy disk to a business backing up an entire
  database on a tape system
• Tape is used often because of its storage
  capacity and its low cost

26
Organizing and Accessing Stored Data

• Levels of Data
• Character is a single letter, digit, or special
  character
• Field contains a set of related characters such
  as a single name, phone number, or grade
• Record is set of related fields. Your student
  record contains your name, personal info, grades,
  etc.
• Files are a collection of related records. All
  of the students records would be a file.
• Database is a collection of all of the files.
  Class information, faculty information, students
  records and all make up the database.

27
Key Fields-Identifying Records

• One field in the record is used to uniquely
  identify the records, called the key field
• Names, product descriptions, phone numbers and
  addresses all make lousy key fields because they
  are rarely unique.
• Most of the time a product ID or social security
  number or an arbitrarily assigned number will act
  as the key

28
Overview of File Plan

• Determine how data will be accessed
• Organize data according to access plan
• Determine storage mechanism according to
  organization plan
• Access determined by the immediate need of the
  data direct if needed immediately
• If immediate, requires indexing and transaction
  processing

29
Methods of File Organization

• Sequential-records are stored in order and
  processed in order by key field
• Direct File Organization- aka random file
  organization allows for direct or random access
  to data anywhere in the file
• Requires a DASD, direct access storage device
• Allows updating in place, does not require
  merging of two datasets to make an update
• Hashing or randomizing algorithm applies math to
  the key and sometimes accidentally results in
  synonyms, two files with the same assigned
  address and results in a collision

30
One More Method of File Organization

• Indexed file organization
• Combines the best of sequential and direct file
• Has a table of storage addresses
• Serves as a directory to that disk

31
Processing the Data

• Transactions are instances where a record needs
  be created, altered, or deleted
• Transaction file keeps list of changes until the
  master file is updated
• Batch processing means all of the transactions
  are held in the transaction file and updated all
  at once

32
Transaction Processing

• Real-time processing
• Data is updated or changed very soon after each
  individual transaction
• Common in banking industry, when you use your
  Texan card, automatic inventory systems, etc.

33
How to choose a method

• If data is needed immediately, transaction is the
  way to. Files are always up to date with new
  information.
• Batch processing is more efficient. It can be
  scheduled as a background job and run when no one
  else is on the system