Computer Books for CSS and PMS free download in PDF 2020

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  • Post last modified:March 28, 2020

Computer Books for CSS and PMS free download

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Some Basics about Computer

Types of External Memory

• Magnetic Disk


• Optical

—CD-Recordable (CD-R)

Magnetic Disk


• Disk substrate coated with magnetizable
material (iron oxide…rust)
• The substrate used to be aluminum
• Now glass

—Improved surface uniformity
– Increases reliability
—Reduction in surface defects
– Reduced read/write errors
—Lower flight heights (See later)
—Better stiffness

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Computer Books for CSS and PMS

Read and Write Mechanisms

• Recording & retrieval via conductive coil called ahead
• May be single read/write head or separate ones
• During read/write, the head is stationary, platter rotates
• Write

— Current through the coil produces a magnetic field
— Pulses sent to head
— The magnetic pattern recorded on the surface below

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• Read (traditional)

— Magnetic field moving relative to coil produces current
— The coil is the same for reading and writing

• Read (contemporary)

— Separate read head, close to writing head
— Partially shielded magneto-resistive (MR) sensor
— Electrical resistance depends on the direction of the magnetic field
— High-frequency operation
– Higher storage density and speed

—Better shock/damage resistance

• Magnetic Tape

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Disk Velocity

• Bit near centre of rotating disk passes fixed point
slower than bit on outside of disk
• Increase spacing between bits in different tracks
• Rotate disk at constant angular velocity (CAV)

—Gives pie shaped sectors and concentric tracks
—Individual tracks and sectors addressable
—Move head to given track and wait for given sector
—Waste of space on outer tracks
– Lower data density

• Can use zones to increase capacity

—Each zone has fixed bits per track
—More complex circuitry

Disk Layout Methods Diagram

Finding Sectors
• Must be able to identify start of track and
• Format disk

—Additional information not available to user
—Marks tracks and sectors

Winchester Disk Format
Seagate ST506

• Fixed (rare) or movable head
• Removable or fixed
• Single or double (usually) sided
• Single or multiple platter
• Head mechanism

—Contact (Floppy)
—Fixed gap
—Flying (Winchester)

Fixed/Movable Head Disk
• Fixed head

—One read write head per track
—Heads mounted on fixed ridged arm

• Movable head

—One read write head per side
—Mounted on a movable arm

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