How data is stored in HDD? detailed explanation
Components of a
Hard Disk Drive (HDD):
Ø Platters:
HDDs contain several circular platters stacked on a spindle. These platters are
typically made of glass or aluminum and are coated with a thin layer of
magnetic material.
Ø Read/Write Heads: Each platter surface has a read/write head
attached to an actuator arm. The heads are very close to the platter surface
but do not touch it when the disk is spinning.
Ø Actuator Arm: The actuator arm positions the read/write
heads over the correct location on the platter to read or write data.
Ø Spindle: The
spindle rotates the platters at a constant speed (measured in rotations per
minute, RPM), typically ranging from 5,400 RPM to 15,000 RPM in modern HDDs.
Data Storage
Mechanism:
Magnetic Storage:
HDDs use magnetism to store and
retrieve data. Each platter surface is divided into tracks (concentric circles)
and sectors (pie-shaped divisions within tracks).
Recording Data:
Ø Writing: When
data is written to an HDD, the magnetic read/write head changes the
magnetization of tiny regions on the platter surface. These regions represent
binary data (0s and 1s).
Ø Binary Data Representation: A magnetic field in one direction (e.g.,
north-south) represents one binary state (e.g., 0), and a magnetic field in the
opposite direction (e.g., south-north) represents the other binary state (e.g.,
1).
Ø Magnetic Coercivity: The ability of the magnetic material to retain
its magnetization over time ensures data integrity.
Reading Data:
Ø Reading: When
data needs to be accessed, the read/write head detects the changes in magnetic
polarization as the platter spins beneath it.
Ø Detection: Changes
in magnetic polarity induce electrical signals in the read/write head, which
are then amplified and decoded into binary data (0s and 1s) by the electronics
of the HDD.
Organization of
Data:
Ø Tracks and Sectors: Data is organized into concentric tracks on
each platter surface. Each track is further divided into sectors, typically 512
bytes each (though this can vary).
Ø File System: Higher-level software (such as the operating
system) organizes data into files and manages the allocation of sectors on the
HDD for storing file data.
Performance
Considerations:
Ø Access Time: The time it takes for the read/write heads to
move to the correct track and for the platter to rotate so that the data sector
is under the head.
Ø Data Transfer Rate: The rate at which data is transferred between
the HDD and the computer’s memory.
Ø Seek Time: The
time it takes for the actuator arm to position the read/write heads over the
correct track.
Summary:
Hard Disk Drives (HDDs) store data
using magnetic storage technology. Data is written and read by changing the
magnetic polarization of regions on spinning platters, organized into tracks
and sectors. The read/write heads, controlled by an actuator arm, access data
quickly and efficiently. Understanding how data is stored in HDDs helps in
appreciating their role as primary storage devices in modern computing systems,
offering large storage capacities at relatively lower costs compared to
solid-state drives (SSDs).
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