Storage Devices
1
Curriculum
• Describe the functional
characteristics of storage
devices in terms of random
or sequential access, volatile
or non-volatile, data transfer
rate and storage capacity.
• Examples of storage devices
magnetic disk, optical disk,
flash memory, magnetic tape
and network storage.
• In understanding the
characteristics of storage
devices, students should be
made aware of the trend to
faster and greater storage
capacity but smaller physical
size over time.
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Classification
3
Random VS Sequential Access
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Sequential Access Memory (SAM)
•
In computing, sequential access memory (SAM) is a class of
data storage devices that read their data in sequence.
•
Sequential access devices are usually a form of magnetic
memory.
•
While sequential access memory is read in sequence, accesses
can still be made to arbitrary locations by "seeking" to the
requested location.
•
It is often relatively inefficient
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Storage Capacity
Unit
Abbr. Value
Kilobyte
KM
1 KB = 210B = 1,024 B (or 1,024 bytes)
Megabyte MB
1 MB = 220B = 1,024 KB (or 1,048,576 bytes)
Gigabyte
GB
1 GB = 230B = 1,024 MB (about 1 billion bytes)
Terebyte
TB
1 TB = 240B = 1,024 GB (about 1 trillion bytes)
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Magnetic
•
It is magnetically coated strip of plastic
•
It is a sequential access memory
•
It is relatively low in speed
•
It allows users to store or transport a lot of data at low cost
Description
Storage
Magnetic Tape
ZIP Disk
MO
♦
♦
♦
♦
♦
♦
♦
♦
Sequential read/write only.
Inexpensive but slow.
Mainly used for backup purpose.
A kind of large capacity magnetic disks.
Not very common
Magneto-Optical (optical and magnetic technology)
Expensive and uncommon storage media.
Can be read from and written to.
Capacity
~24GB with compression
100MB, 250MB
650MB, 1.3GB
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Flash memory
• It is a non-volatile computer storage chip
• It is primarily used in memory cards, USB flash
drives, MP3 players and solid-state drives
• It is a specific type of EEPROM (electrically erasable
programmable read-only memory) that is erased
and programmed in large blocks
• It is a direct access memory
Storage
USB Drive
Memory cards
Description
♦ Using chip to store data.
♦ Plug and play for latest OS; device driver needed for older OS.
♦ Comparatively expensive.
♦ Using chip to store data.
♦ Specially design card reader is required
♦ Used in digital camera, PDA, etc.
♦ Expensive.
♦ Common types are: Compact Flash (CF), Smart Media (SM),
MultiMedia Card (MMC), Memory Stick (MS), Secure Digital (SD)
Capacity
128MB – 1024MB
16MB – 2048MB
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Optical
•
It is round plastic disk coated with a metallic surface
•
Data can be stored and accessed via red-light laser technology
•
It is an non-volatile memory
•
It is a direct access memory
Storage
CD-ROM
CD-R
CD-RW
DVD-ROM
DVD-R
DVD-RW
Description
♦ Using compact disc for storage.
♦ READ-ONLY!!
♦ Note: Audio CD stores audio instead of “data”.
♦ CD-Recordable / -ReWritable
♦ It requires specially designed drive for recording, but normal CD-ROM drive can
read it.
♦ Data recorded on CD-R CANNOT be erased or overwritten. However, unused
area can still store data.
♦ Data on CD-RW can be erased
♦ Originally designed for storing high quality video.
♦ READ-ONLY!!
♦ DVD-Recordable / -ReWritable
♦ (Other formats: DVD-RW, DVD+R, DVD-RAM)
♦ It requires specially designed drive for recording, but normal DVD-ROM drive can
read it.
♦ Data recorded on DVD-R CANNOT be erased or overwritten. However, unused
area can still store data.
♦ Data on DVD-RW can be erased.
♦ Drives and disks are more expensive.
Capacity
650MB
650MB, 700MB
4.7GB, 9.4GB, 8.5GB, 17GB
4.7GB, 9.4GB, 8.5GB, 17GB
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