day 4: data storage (ppt)
TRANSCRIPT
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Data Storage
CSci 131Sept. 12, 2006
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Outline
Bytes Main Memory Mass Storage Comparison Quiz1 – 10 min
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Bit Review Flip-flops and capacitors provide means
for storing a bit Flash memory – electrons are trapped
inside tiny chambers Two states are full or empty chambers
Flip flops, cores, capacitors are forms of dynamic memory
Flash memory holds the data “permanently”
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Bytes Byte is 8 ordered bits
10000000 and 00000001 are different The left end is the high-order end and the
leftmost bit is the most significant bit The right end is the low-order end and the
rightmost bit is the least significant bit
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Storage Measurements
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Example
A file is 5,376,000 bytes long How many kilobytes (KB) is this?
How many megabytes (MB) is this?
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Main Memory Main memory is a sequence of cells
that can hold 1 byte Each cell has a unique numerical
address Main memory is ordered
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Main memory Consecutive bytes (cells) are used for
larger data
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Properties of main memory Random Access Memory – RAM
each cell or memory location can be referenced, accessed, or modified in the same amount of time
Memory is very fast Access time is measured in
nanoseconds Memory is volatile
Contents disappear when power is gone
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Mass Storage
Also called Secondary Memory Much larger and cheaper than RAM Data contents remain after power is
disconnected Access times are slower (in
milliseconds) since secondary storage relies on mechanical motion
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Types of Mass Storage
Hard disk Floppy disk Zip Disk CD DVD Flash drive
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Disk Storage Each surface of a disk has magnetic
coating The surface is divided into rings called
tracks Each track is broken down into
sectors Every track on a disk has the same
number of sectors Each sector holds the same amount of
data
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Disk Storage
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Disk Storage
Disk spins while a read/write head moves in and out to view different areas
Types: Hard disks: not removable, fast,
primary storage Floppy/Zip disks: removable, slower,
used for distribution or backup
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Disk Access
Move read/write head to proper track
Wait for disk to spin and sector to move under read/write head
Read from (write to) the sector as it passes under the read/write head
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Disk Access Terms
Seek time: time to move read/write head between tracks
Latency time: time for ½ disk rotation
Access time: seek time + latency time
Transfer rate: rate at which data can be transferred to/from disk
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Compact Disc (CD) Uses optical technology instead of
magnetic discs Each CD is a spinning, 5 in. diameter
disc with reflective material and protective coating
Writing requires a laser creating variations on the surface
Reading uses a laser and mirrors to monitor the surface of the CD
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Compact Disc (CD)
CD is a single track that spirals where a hard drive was multi-track
All sectors are the same size Benefit of better storage space use Drawback of slower access time
Main types: CD-ROM, CD-R, CD-RW, DVD
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Tape Storage Long plastic band with magnetic
coating Organized into blocks separated by
inter-record gaps Blocks store data Inter-record gaps help seeking
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Tape Storage Tape access is linear. Tape must be wound until needed block is
under the read/write head. Tapes are slow but can hold large amounts
of data Used primarily as backups for hard drives
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Comparison
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Assignment for 09/14
Read Sections 1.4, 1.5 HW1 due Thurs. 14 (next class) Quiz1 now
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Main Memory
Want as much fast storage as possible But RAM is volatile Disk slower but larger and non-volatile Cost Engineering Why 1GB of RAM? 100 GB hard-drive?