The document discusses data storage devices, focusing on hard disk drives (HDDs). It describes how HDDs store data using magnetic platters and read/write heads. HDDs allow random access to individual blocks of data and come in portable and fixed varieties that can range from gigabytes to terabytes of storage. Common performance metrics for HDDs are data rate, or bytes/second delivered to the CPU, and seek time, the time to retrieve a requested file. The document outlines the history and major producers of HDDs.

1. “Computer & Computation”
 Muhammad Muneeb
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3. DATA:
 Unorganized collection of facts which is able to be organized
into useful information.
Storage:
Storage holds data, instructions, and information for future
use.
 For example, computers can store hundreds or millions of
customer names and addresses. Storage holds these items
permanently.
Storage devices:
Hardware components that read data from and write data to
storage media called storage devices.
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4. There are three types of storage devices.
1) Magnetic Storage Devices
2) Optical Storage Devices
3) Solid-State Storage Devices:
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5.  Such devices, coated with magnetically
sensitive material (i.e. Iron Oxide that react to a
magnetic material)
 Uses magnet to access data
 Use binary relation to store data (1 and 0 form)
 The storage capacity is unlimited.
 Magnetic disk are less vulnerable to data
corruption due to careless handling.
 E.g. (Floppy Disk, Hard Disk)
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7.  Use laser to read data and write data to the
reflective surface of optical disc
 They are better storage medium than magnetic
storage devices.
 Optical disc storage system consists of a
metallic or plastic disk.
 Due to there compact size and light weight,
optical disks are easy to handle store and port
from one place to another.
 E.g. (CD, DVD, And Blue Ray Disc)
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9.  Non volatile
 Less Expensive from blue rays
 High Speed
 They stored data on memory circuits rather
than disk or tapes.
 They store data electronically not in a magnetic
or optical form.
 They don’t need to move a head or sensor to
find data.
 E.g. ( Flash drive, Memory Cards)
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11. Hard Disk
Drive
(HDD)
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12. “Introduced by IBM in 1956 became the
dominant secondary storage device for
general purpose computers by the early
1960s”
 Data storage device for storing and retrieving
digital information using platters (rapidly rotating
disks).
 Non volatile.
 Individual blocks of data can be stored or retrieved
in any order rather than sequentially.
 It consist one or more rigid platters.
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13. There are just a large shiny circular plates of
magnetic material called platter, divided into
billions of areas. Each one of these areas can
be independently magnetized to store disk
drive (HDD) records the data by magnetizing
ferromagnetic material directionally to
represent either 0 or 1 binary digit. They read
the data back by magnetization of the
material.
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14. There are two ways to measure the performance
of a hard disk.
1) Data rate:
It is the number of bytes per seconds
that the drive can delivers to the CPU the rate
between 5 and 40 megabytes are common.
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15. 2) Seek Time:
The seek time is the amount of time
between when the CPU request the file and
when the first byte of the file is sent to the
CPU. Times Between 10 and 20 milliseconds
are common.
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16.  More than 200 companies have manufactured HDDs
over time.
 Most popular production companies today:
Western Digital, Seagate, and Toshiba.
 Worldwide revenues for disk storage were $32 billion
in 2013, down about 3% from 2012..
 The estimated 2013 market shares are about 40–45%
each for Seagate and Western Digital and 13–16% for
Toshiba.
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17. There are types of hard drive.
1) ZIP/ Bernoulli disk.
2) Disk pack.
3) Winchester Disk.
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18.  Consist of single hard disk platter.
 Storage capacity 8GB to 500GB or more
 May be portable or fixed.
 The fixed type is connected permanently.
 Portable type is connected to computer during
use and then after use it can be disconnected.
 It can be loaded/Unloaded into a Zip drive as
we insert/remove a video cassette into video
cassette player.
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20.  Consists of multiple hard disk platter.
 All disk revolved together around single
central shaft.
 When not in use user can store a disk pack off-
line in a plastic case.
 This gives virtually unlimited storage capacity
to disk pack.
 Storage capacity of disk pack varies from
hundred GB to several Thousand GB.
 Diameter 14-inch introduced by IBM.
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22.  Consists of multiple Hard disk platters
Mounted on a single central shaft.
 Its hard disk platters and disk drive are sealed
together and can not be separated from each
other.
 Have large storage capacity because all
surfaces of all disk platters are used for data
recording.
 Storage capacity varies from few gigabits to
few terabits.
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