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Lecture # 7
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Topics
Storage Techniques of Bits Mass Storage Disk System Performance File Storing Fractions Data Compression Communication Errors
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Storage of Bits
Gate: A device that computes a Boolean operation Often implemented as (small) electronic
circuits in which voltage levels indicate 0’s and 1’s
Provide the building blocks from which computers are constructed
VLSI (Very Large Scale Integration)
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Figure 1.2 A pictorial representation of AND, OR,
XOR, and NOT gates as well as their input and output values
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Mass Storage
In computing, mass storage refers to the storage of large amounts of data in a persisting and machine-readable fashion.
Storage media for mass storage include hard disks, floppy disks, flash memory, magnetic disks, Optical Disks (CD’s, DVD’s), magnetic tape etc
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Mass storage includes devices with removable and non-removable media.
It does not include random access memory (RAM), which is volatile in that it loses its contents after power loss.
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Advantage over RAM
Less volatile Large Storage Capacity
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Mass Storage
On-line versus off-line Typically larger than main memory Typically less volatile than main
memory Typically slower than main memory
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Mass Storage Systems
Magnetic Systems Disk Tape
Optical Systems CD DVD
Flash Drives
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Magnetic Disk
Thin disk with magnetic coating Read/ write Heads Head traverses circle called “Track” Tracks divided into Sectors Information of Tracks and Sectors
setup by formatting disk
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Magnetic Disk
Lower Capacity Systems e.g Floppy Disk
High Capacity Systems e.g Hard Disk
Hard Disk contains 5-10 disks mounted on a spindle rigidly
To allow for Faster Speed the Head is floating above the surface
“Head Crash” due to dust particles
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Disk System Performance
Seek Time: Time required by the R/W head to move from one track to another
Rotational Delay / Latency Time: Half the time required by the disk
to make one complete rotation Access Time: Seek Time +
Rotational Delay Transfer Rate: rate at which data
transferred to another disk
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Figure 1.9 A magnetic disk storage system
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Figure 1.10 Magnetic tape storage
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Figure 1.11 CD storage
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Files
File: A unit of data stored in mass storage system Fields and keyfields
Physical record versus Logical record
Buffer: A memory area used for the temporary storage of data (usually as a step in transferring the data)
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Figure 1.12 Logical records versus physical
records on a disk