Storage Devices Powered by DeSiaMore1. Contents Storage Primary Secondary Access Method Floppy disk...
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Transcript of Storage Devices Powered by DeSiaMore1. Contents Storage Primary Secondary Access Method Floppy disk...
Storage Devices
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Contents
• Storage
• Primary
• Secondary
• Access Method
• Floppy disk
• Hard disk
• Optical disks
• Magnetic media
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Overview
Information storage For future To share To modify
Permanent Storage secondary
storage, nonvolatile
Temporary storage RAM volatile
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Secondary Storage
1. Secondary storage provides permanent or non-volatile storage:
2. This is accomplished by writing files to and reading from the secondary storage device.
• Writing- Is the process of serving information to the secondary storage device.
• Reading- Is the process of accessing information from secondary storage.
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Characteristics of Secondary Storage devices
• Media or medium which is the actual physical material that holds the data and programs
• Capacity measures how much a particular storage medium can hold
• Storage device are hardware that reads data and programs from storage media. Most also write to storage medium
• Access speed or access time measures the amount of time required by the storage devices to retrieve data and program.
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Storage devices can be categorized as magnetic or optical
Magnetic storage are such as diskettes, hard disk, high capacity floppy disks, and magnetic tapes
Optical storage are compact disks CD-ROM, DVD-ROM, CD-R, CD-RW etc
Categories of Storage Devices
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Floppy Disks
• Floppy disks are often called diskettes or simply disks.
• They are portable and removable storage media
• They use flat circular pieces of Mylar plastic that have been coated with magnetic material.
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Traditional Floppy Disk
Traditional floppy disks:
1.44MB
3.5 inch
2HD-two side high density
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How a Disk Drive Works
Metal shutter
Hard plastic jacket
Label
Write protection notch in the open position
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Hard Disks
Metallic disks Composed of metallic rather than plastic disks Fast information storage and retrieval (write and
read) Read-write heads
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Materials that can cause a Materials that can cause a head crashhead crash
Materials that can cause a Materials that can cause a head crashhead crash
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Internal Hard Disk Inside system unit for storing the
operating system, other programs and large data files.
Motor with access arm and read-write heads.
Many advantages over floppy disks. Capacity (up to thousands
times a single floppy) Speed (twenty times the
speed)
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Hard-Disk Packs
Removable, massive storage capacity
Common in mainframes Resembles stack of record albums
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Optical disks use laser technology. CD and DVD are optical disk formats.
Compact, high capacity form of permanent storage
Laser beam writes by creating a pattern of pits (holes) and lands (flat areas) to encode data bits
Laser beams reflect off the pits and lands to read the data
Optical Disks
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CD-ROM
Compact disc-read-only memory
Not written to
650 MB capacity
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CD-R & CD-RW
CD-Recordable or WORM
(write once, read many)
CD-RW or rewritable optical discs
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DVD
Digital Versatile Disk or Digital Video Disk
Up to 4.7 gigabytes a capacity, seven times CD DVD-ROM- provide high quality, movie length videos
DVD-R- consumer recordable version
DVD-RAM or DVD-RW- rewritable version of 2.6 to 5.2 GB storage capacity
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Magnetic Tape
Disks offer fast, direct access to data programs Tapes offer sequential access (fast forwarded or rewound)
Storage and backup Forms of tape storage are:
Magnetic tape streamers Magnetic tape reels
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Backup tape cartridge units used with
microcomputer systems
Capacities range from 120 MB to 5 GB
Magnetic Tape Streamers
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Magnetic Tape Reels
Used with minicomputer and mainframe
computers
Often 1/2 inch wide and 1/2 mile long
Stores 1600 to 6400 characters per inch
Tapes are run on magnetic tape drives or
magnetic tape units
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