Transcript Chapter 4: Storage Hardware

Storage Hardware
Chapter 4
Preserving Data and
Information
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Overview
• Storage
fundamentals
• Tape storage
• Diskette storage
• Hard disk storage
• Optical storage
• Backup
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Storage Fundamentals
• What is the difference
between primary and
secondary storage?
• What are the basic types
of files?
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Save Your Files
• Save your files to secondary
storage
• One can think of file storage
as a file cabinet
– drawers
– folders
• Calling up a file actually
calls up a copy of a file, until
it is modified or saved
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Save Your Files
• Helpful hints
– you are in charge of file organization
– electronic file organization is easier that
physical file organization
• use names to keep track of versions
• organize in folders the way you reference and use
files
• backup, backup, backup
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Common Elements of Storage
Technology
• Amount of data in a file is usually
expressed in kilobytes or megabytes
• Total amount of data in a storage area that
includes multimedia/video maybe measured
in gigabytes
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Storage Technology
• Retrieving files into RAM is
called reading
– loading an application
– opening a file
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Storage Technology (continued)
• Copying data from RAM onto
a secondary storage device
called writing
• Sequential storage
– magnetic tape
– random accessing sequential
data is time consuming
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Storage Technology (continued)
• Direct access storage
– faster than sequential access
• Indexed-sequential
– stores data sequentially
– are indexed
– a combination of sequential and
direct access storage methods
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File Types
• Program files
– source files
– executable files
• Data files
– also called document files
– contain only data
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File Types (continued)
• ASCII files
– text-only
– ASCII code is one of the
most common codes
• Image files
– digitized graphics in such
formats as GIF, JPEG
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File Types (continued)
• Audio and video files
– digitized sound and
video
– WAV, MP3, MPEG,
AVI
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File Descriptors
• Files have unique names
• Windows-based systems have a threecharacter extension
• Macintosh, UNIX, and Linux-based systems
do not use extensions
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File Descriptors: Identification
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Tracking files
• File tables
– File Allocation Tables (FAT)
• keep track of where data is stored
• each type must be coordinated with hard disk size
– FAT or FAT-16, Windows 95
– FAT-32, Windows 95 OSR/2, Windows 98 and
later
– NTFS, Windows NT
– HPFS, IBM OS/2
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File Management
• Copying
• Renaming
• Deleting
– some corporations do not
allow deletion of files by
individuals
• Printing
• Import/Export
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Tape Storage
• Reels for mainframes
• Cartridge tape units or tape
streamers
– QIC
• quarter-inch tapes up to 20 GB
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Tape Storage Options
• DAT
– Digital audio tape up to 24 GB
• DLT
– Digital linear tape up to 70 GB
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Diskette Storage
• Diskette or
floppy disk
– 3 ½” = 1.44
MG are
inexpensive
– called HD
high-density
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Large Capacity Diskettes
• Zip (100 MB and 250 MB)
• Imation SuperDisks or LS-120
(120 MB) and Sony HiFD (200
MB)
– drives can accept 1.44 MB
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Diskette functionality
• Tracks and sectors
• Unformatted
• Formatted
– or initialized (Macintosh)
– formatting will erase all
previous data on disk
• Write-protected
– two open holes
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Care and Feeding of Diskettes
• Don’t touch diskette surfaces
• Be careful with the protective plate
– best to carry within a plate diskette holder
• Handle gently
• Avoid sun and heat
• Don’t leave a diskette in the drive
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Hard Disks
• What are the characteristics of hard disks,
and what types of hard disks are available?
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Hard Drive Characteristics
• Common 10 to 20 GB size
• 10 GB hard drive stores
approximately 3 million pages of
information
• Multimedia and graphics-oriented
requirements will quickly fill up any
hard drive
• Tightly sealed disks covered with
magnetic material
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Internal Hard Drives
• Internal to system
– connected via IDE, SCSI, or
controller (host adapter) interface
to motherboard
– some computers can support two
internal hard drives
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EIDE
• EIDE or Enhanced Integrated Drive
Electronics
– each port can support a CD-ROM or optical
disk drive
– native EIDE 16.6 MG transfer rate
– Ultra DMA (direct memory access) if drive and
motherboard built for these newer standards
• uses same EIDE port
• 33 MG per second
• 66 MG per second, using newer cable type
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SCSI
• SCSI (pronounced “scuzzy”)
– small computer system interface
– used first on Macs
– used on PCs with SCSI adapter card or built-in
SCSI
– maximum SCSI transfer rates vary from 20 to
160 MB depending on standard
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EIDE or SCSI?
• With Ultra DMA 66 for EIDE
ports, there is no longer a simple
answer to which type is faster EIDE or SCSI
• Depends on the standard being
used, type of data being recorded,
and traffic along the SCSI chain
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Hard Disk Variations
• External hard drives
– via parallel port, SCSI interface, or
USB interface
• Removable disks
– also called removable hard disks
– SyQuest SyJet
– Iomega’s Zip and Jaz
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Using Hard Disk Technology
• Virtual memory
– Hard disk space is used to extend
main memory (RAM)
• Removable packs
– up to 20 hard drive platters for
large system use
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More HD technology
• Fixed disk storage
– up to 100 disks in one cabinet
• RAID
– redundant array of inexpensive
disks
– storage system with fail-safe
system technology
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Hard Disk Future
• MR Head
– separates read and write
functions into two physically
separate heads
– will improve performance in the
foreseeable future
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Optical Disks
• What are optical disks, and
how are they used?
• Uses laser technology,
rather than magnetic oxide
to store data
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Types
• CD-ROM
– compact-disk-only memory
• CD-R
– compact disk-recordable
– write once only
• CD-RW
– compact disk-rewritable
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CD Advantages
• CD-R and CD-RW drives can read CDROMs
• Better quality audio than traditional tape
• CD-R and CD-RW can be used for system
and file backup
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More Types
• DVD/DVD-ROM
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–
–
–
–
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Digital video disk
Digital versatile disk
Stores up to 17 GB
rewritable DVD types are being developed
all should be able to play any CD
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DVD Advantages
•
•
•
•
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More storage capacity
Better audio
Better video
Future recordable and
rewriting capabilities
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Backup
• Why backup?
• All disks/systems crash
– it is just a matter of time for hard disks,
floppies, and systems
– large systems survive because they are
sustainable
• since all disks crash, automatic full-backups and
incremental backups insure minimum interruption of
business operations
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Why do they crash?
• Systems
– complexity is inherent in systems
• Hard drives, floppies, and storage media
– these are physical items that wear out
– with average use
• tape lasts 5 to 15 years
• Zip disks 10 years
• floppies 5 to 10 years
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Other Forms of Secondary
Storage
• Flash memory
• flash RAM
• no moving parts
• up to 100 MB
• Advanced storage technology
• manufacturers pushing physical limits
• IBM developing optical system that can
store 350 million bits a square inch
• NEC physicists developing storage media
that may be atoms thick
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