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PostSubject: What is Hard disk drive?   Fri Aug 01, 2008 9:31 am

What is Hard disk drive?

A hard disk drive (HDD), commonly referred to as a hard drive, hard disk or fixed disk drive, is a non-volatile storage device which stores digitally encoded data on rapidly
rotating platters with magnetic surfaces. Strictly speaking, "drive"
refers to a device distinct from its medium, such as a tape drive and
its tape, or a floppy disk drive and its floppy disk. Early HDDs had
removable media; however, an HDD today is typically a sealed unit with fixed media.

hdd were originally developed for use with computers. In the 21st century,
applications for HDDs have expanded beyond computers to include digital
video recorders, digital audio players, personal digital assistants,
digital cameras and video game consoles. In 2005 the first mobile
phones to include HDDs were introduced by Samsung and Nokia. The need
for large-scale, reliable storage, independent of a particular device,
led to the introduction of configurations such as RAID arrays, network
attached storage (NAS) systems and storage area network (SAN) systems
that provide efficient and reliable access to large volumes of data.

record data by magnetizing ferromagnetic material directionally, to
represent either a 0 or a 1 binary digit. They read the data back by
detecting the magnetization of the material. A typical HDD design
consists of a spindle which holds one or more flat circular disks
called platters, onto which the data is recorded. The platters are made
from a non-magnetic material, usually glass or aluminum, and are coated
with a thin layer of magnetic material. Older disks used iron(III)
oxide as the magnetic material, but current disks use a cobalt-based

platters are spun at very high speeds. Information is written to a
platter as it rotates past mechanisms called read-and-write heads that
operate very close over the magnetic surface. The read-and-write head
is used to detect and modify the magnetization of the material
immediately under it. There is one head for each magnetic platter
surface on the spindle, mounted on a common arm. An actuator arm (or
access arm) moves the heads on an arc (roughly radially) across the
platters as they spin, allowing each head to access almost the entire
surface of the platter as it spins. The arm is moved using a voice coil
actuator or (in older designs) a stepper motor.

magnetic surface of each platter is divided into many small
sub-micrometre-sized magnetic regions, each of which is used to encode
a single binary unit of information. In today's HDDs each of these
magnetic regions is composed of a few hundred magnetic grains. Each
magnetic region forms a magnetic dipole which generates a highly

field nearby. The write head magnetizes a magnetic region by generating
a strong local magnetic field nearby. Early HDDs used an electromagnet
both to generate this field and to read the data by using
electromagnetic induction. Later versions of inductive heads included
metal in Gap (MIG) heads and thin film heads. In today's heads, the
read and write elements are separate but in close proximity on the head
portion of an actuator arm. The read element is typically
magneto-resistive while the write element is typically thin-film

modern drives, the small size of the magnetic regions creates the
danger that their magnetic state be lost because of thermal effects. To
counter this, the platters are coated with two parallel magnetic
layers, separated by a 3-atom-thick layer of the non-magnetic element
ruthenium, and the two layers are magnetized in opposite orientation,
thus reinforcing each other. Another technology used to overcome
thermal effects to allow greater recording densities is perpendicular
recording, which has been used in many hard drives as of 2007.

disk drives are sealed to prevent dust and other sources of
contamination from interfering with the operation of the hard disks
heads. The hard drives are not air tight, but rather utilize an
extremely fine air filter, to allow for air inside the hard drive
enclosure. The spinning of the disks causes the air to circulate
forcing any particulates to become trapped on the filter. The same air
currents also act as a gas bearing which enables the heads to float on
a cushion of air above the surfaces of the disks.

Capacity and access speed

rigid disks and sealing the unit allows much tighter tolerances than in
a floppy disk drive. Consequently, hard disk drives can store much more
data than floppy disk drives and can access and transmit it faster. In
2007, a typical “enterprise”, i.e. workstation HDD, might store between
160 GB and 1 TB of data (as of local US market by July 2007), rotate at
7,200 or 10,000 revolutions per minute (RPM) and have a media transfer
rate of 1 Gbit/s or higher. The fastest “enterprise” HDDs spin at
15,000 rpm, and can achieve sequential media transfer speeds above 1.6
Gbit/s. Mobile, i.e., laptop HDDs, which are physically smaller than
their desktop and enterprise counterparts, tend to be slower and have
less capacity. In the 1990s, most spun at 4,200 rpm. In 2007, a typical
mobile HDD spins at 5,400 rpm, with 7,200 rpm models available for a
slight price premium.

exponential increases in disk space and data access speeds of HDDs have
enabled the commercial viability of consumer products that require
large storage capacities, such as digital video recorders and digital
audio players. In addition, the availability of vast amounts of cheap
storage has made viable a variety of web-based services with
extraordinary capacity requirements, such as free-of-charge web search
and email (Google, Yahoo!, etc.).

main way to decrease access time is to increase rotational speed, while
the main way to increase throughput and storage capacity is to increase
areal density. A vice president of Seagate Technology projects a future
growth in disk density of 40% per year. Access times have not kept up
with throughput increases, which themselves have not kept up with
growth in storage capacity.

As of 2006, some disk drives use perpendicular recording technology to increase recording density and throughput.

first 3.5" HDD marketed as able to store 1 TB was the Hitachi Deskstar
7K1000. It contains five platters at approximately 200 GB each,
providing 935.5 GiB of usable space. Hitachi has since been joined by
Samsung (Samsung SpinPoint F1, which has 3 × 334 GB platters), Seagate
and Western Digital in the 1 TB drive market.

Form factor
Largest capacity
Platters (Max)

5.25" FH
146 mm
47 GB (1998)

5.25" HH
146 mm
19.3 GB (1998)

102 mm
1 TB (2007)

69.9 mm
500 GB (2008)

1.8" (PCMCIA)
54 mm
160 GB (2007)

1.8" (ATA-7 LIF)
53.8 mm

36.4 mm
40 GB (2008)

Capacity measurements

capacity of an HDD can be calculated by multiplying the number of
cylinders by the number of heads by the number of sectors by the number
of bytes/sector (most commonly 512). Drives with ATA interface bigger
and more than eight gigabytes behave as if they were structured into
16383 cylinders, 16 heads, and 63 sectors, for compatibility with older
operating systems. Unlike in the 1980s, the cylinder, head, sector
counts reported to the CPU by a modern ATA drive are no longer actual
physical parameters since the reported numbers are constrained by
historic operating-system interfaces and with zone bit recording the
actual number of sectors varies by zone. Disks with SCSI interface
address each sector with a unique integer number; the operating system
remains ignorant of their head or cylinder count.

Hard disk drive manufacturers specify disk capacity using the SI prefixes mega-, giga- and tera-, and their abbreviations M, G and T. Byte is typically abbreviated B.

operating-system tools report capacity using the same abbreviations but
actually use binary prefixes. For instance, the prefix mega-, which
normally means 106 (1,000,000), in the context of data storage can mean 220
(1,048,576), which is nearly 5% more. Similar usage has been applied to
prefixes of greater magnitude. This results in a discrepancy between
the disk manufacturer's stated capacity and the apparent capacity of
the drive when examined through some operating-system tools. The
difference becomes with 7% even more noticeable for a gigabyte. For
example, Microsoft Windows reports disk capacity both in decimal-based
units to 12 or more significant digits and with binary-based units to
three significant digits. Thus a disk specified by a disk manufacturer
as a 30 GB disk might have its capacity reported by Windows 2000 both as "30,065,098,568 bytes" and "28.0 GB". The disk manufacturer used the SI definition of "giga", 109 to arrive at 30 GB; however, because the utilities provided by Windows define a gigabyte as 1,073,741,824 bytes (230 bytes, often referred to as a gibibyte, or GiB), the operating system reports capacity of the disk drive as (only) 28.0 GB.
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PostSubject: Re: What is Hard disk drive?   Fri Aug 01, 2008 9:32 am

Form factors

The earliest “form factor” hard disk drives inherited their dimensions from floppy-disk drives (FDDs),
so that either could be mounted in chassis slots, and thus the HDD form
factors became colloquially named after the corresponding FDD types.
"Form factor" compatibility continued after the 3½ in size even though
floppy disk drives with new smaller dimensions ceased to be offered.

* "8 inch" drive: (9.5 in x 4.624 in x 14.25 in = 241.3 mm x 117.5 mm x 362 mm)
In 1979, Shugart Associates'
SA1000 was the first form factor compatible HDD, having the same
dimensions and a compatible interface to the 8" FDD. Both "full height"

and "half height" (2.313 in) versions were available.

* "5¼ inch" drive: (5.75 in x 1.63 in x 8 in = 146.1 mm x 41.4 mm x 203 mm)

This smaller form factor, first used in an HDD by Seagate in 1980, was
the same size as full height 5¼-inch diameter FDD, i.e., 3.25 inches
high. This is twice as high as commonly used today; i.e., 1.63 in =
41.4 mm (“half height”). Most desktop models of drives for optical 120
mm disks (DVD, CD)
use the half height 5¼" dimension, but it fell out of fashion for HDDs.
The Quantum “Bigfoot” HDD was the last to use it in the late 1990s,
with “low-profile” (~25 mm) and “ultra-low-profile” (~20 mm) high

* "3½ inch" drive: (4 in x 1 in x 5.75 in = 101.6 mm x 25.4 mm x 146 mm)

This smaller form factor, first used in an HDD by Rodime in 1984, was
the same size as the "half height" 3½ FDD, i.e., 1.63 inches high.
Today has been largely superseded by 1-inch high “slimline” or
“low-profile” versions of this form factor which is used by most
desktop HDDs.

* "2½ inch" drive: (2.75 in x 0.374 in x 3.945 in = 69.85 mm x 9.5 mm x 100 mm)

This smaller form factor was introduced by PrairieTek in 1988; there is
no corresponding FDD. It is widely used today for hard-disk drives in
mobile devices (laptops, music players, etc.). Today, the dominant
height of this form factor is 9.5 mm, but there were also 19 mm, 17 mm,
and 12.5 mm high variants in use.

* "1.8 inch" drive: (54 mm × 8 mm × 71 mm)

This form factor, originally introduced by Integral Peripherals in
1993, has evolved into the ATA-7 LIF with dimensions as stated. It is
increasingly used in digital audio players and subnotebooks. An original variant exists for 2–5 GB sized HDDs that fit directly into a PC card expansion slot.

* "1 inch" drive: (42.8 mm × 5 mm × 36.4 mm)
This form factor was introduced in 1999 as IBM's Microdrive to fit inside a CF Type II slot.

* "0.85 inch" drive: (24 mm × 5 mm × 32 mm)
Toshiba announced this form factor in January 2004 for use in mobile phones and similar applications, including SD/MMC slot compatible HDDs optimized for video storage on 4G handsets. Toshiba currently sells a 4 GB (MK4001MTD) and 8 GB (MK8003MTD) version and holds the Guinness World Record for the smallest harddisk drive.

manufacturers discontinued the development of new products for the
1-inch and 0.85-inch form factors in 2007, due to falling prices of
flash memory.

inch-based nickname of all these form factors usually do not indicate
any actual product dimension (which are for more recent form factors
specified in millimeters), but just roughly indicate a size relative to
disk diameters, in the interest of historic continuity.

Access and interfaces

disk drives are accessed over one of a number of bus types, including
parallel ATA (PATA, also called IDE or EIDE), Serial ATA (SATA), SCSI,
Serial Attached SCSI (SAS), and Fibre Channel. Bridge circuitry is
sometimes used to connect hard disk drives to buses that they cannot
communicate with natively, such as IEEE 1394 and USB.

in the days of the ST-506 interface, the data encoding scheme was also
important. The first ST-506 disks used Modified Frequency Modulation
(MFM) encoding, and transferred data at a rate of 5 megabits per
second. Later on, controllers using 2,7 RLL
(or just "RLL") encoding increased the transfer rate by 50%, to 7.5
megabits per second; this also increased disk capacity by fifty percent.

ST-506 interface disk drives were only specified by the manufacturer to
run at the lower MFM data rate, while other models (usually more
expensive versions of the same basic disk drive) were specified to run
at the higher RLL data rate. In some cases, a disk drive had sufficient
margin to allow the MFM specified model to run at the faster RLL data
rate; however, this was often unreliable and was not recommended. (An
RLL-certified disk drive could run on a MFM controller, but with 1/3
less data capacity and speed.)

Enhanced Small Disk Interface
(ESDI) also supported multiple data rates (ESDI disks always used 2,7
RLL, but at 10, 15 or 20 megabits per second), but this was usually
negotiated automatically by the disk drive and controller; most of the
time, however, 15 or 20 megabit ESDI disk drives weren't downward
compatible (i.e. a 15 or 20 megabit disk drive wouldn't run on a 10
megabit controller). ESDI disk drives typically also had jumpers to set
the number of sectors per track and (in some cases) sector size.

originally had just one speed, 5 MHz (for a maximum data rate of five
megabytes per second), but later this was increased dramatically. The
SCSI bus speed had no bearing on the disk's internal speed because of
buffering between the SCSI bus and the disk drive's internal data bus;
however, many early disk drives had very small buffers, and thus had to
be reformatted to a different interleave (just like ST-506 disks) when
used on slow computers, such as early IBM PC compatibles and early Apple Macintoshes.

disks have typically had no problems with interleave or data rate, due
to their controller design, but many early models were incompatible
with each other and couldn't run in a master/slave setup (two disks on
the same cable). This was mostly remedied by the mid-1990s, when ATA's
specification was standardised and the details began to be cleaned up,
but still causes problems occasionally (especially with CD-ROM and
DVD-ROM disks, and when mixing Ultra DMA and non-UDMA devices).

ATA does away with master/slave setups entirely, placing each disk on
its own channel (with its own set of I/O ports) instead.

1394 and USB(1.0/2.0) HDDs are external units containing generally ATA
or SCSI disks with ports on the back allowing very simple and effective
and mobility. Most FireWire/IEEE 1394 models are able to daisy-chain in
order to continue adding peripherals without requiring additional ports
on the computer itself.


Shugart Associates System Interface
Historical predecessor to SCSI.

Small Computer System Interface
Bus oriented that handles concurrent operations.

Serial Attached SCSI
Improvement of SCSI, uses serial communication instead of parallel.


Historical Seagate interface.


Historical Seagate interface (minor improvement over ST-506).

Enhanced Small Disk Interface
Historical; backwards compatible with ST-412/506, but faster and more integrated.

Advanced Technology Attachment
to ST-412/506/ESDI by integrating the disk controller completely onto
the device. Incapable of concurrent operations.

Serial ATA
Improvement of ATA, uses serial communication instead of parallel.
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PostSubject: Re: What is Hard disk drive?   Fri Aug 01, 2008 9:34 am


to the extremely close spacing between the heads and the disk surface,
any contamination of the read-write heads or platters can lead to a head crash
— a failure of the disk in which the head scrapes across the platter
surface, often grinding away the thin magnetic film and causing data
loss. Head crashes can be caused by electronic failure, a sudden power
failure, physical shock, wear and tear, corrosion, or poorly
manufactured platters and heads.

The HDD's spindle system relies on air pressure inside the enclosure to support the heads at their proper flying height
while the disk rotates. An HDD requires a certain range of air
pressures in order to operate properly. The connection to the external
environment and pressure occurs through a small hole in the enclosure
(about 0.5 mm in diameter), usually with a carbon filter on the inside
(the breather filter, see below). If the air pressure is too
low, then there is not enough lift for the flying head, so the head
gets too close to the disk, and there is a risk of head crashes and
data loss. Specially manufactured sealed and pressurized disks are
needed for reliable high-altitude operation, above about 3,000 m
(10,000 feet). Note that modern commercial aircraft have a pressurized cabin, whose pressure altitude
does not normally exceed 2,600 m(8,500 feet) - thus, ordinary hard
drives can safely be used in flight. Modern disks include temperature
sensors and adjust their operation to the operating environment.
Breather holes can be seen on all disks — they usually have a sticker
next to them, warning the user not to cover the holes. The air inside
the operating disk is constantly moving too, being swept in motion by
friction with the spinning platters. This air passes through an
internal recirculation (or "recirc") filter to remove any leftover
contaminants from manufacture, any particles or chemicals that may have
somehow entered the enclosure, and any particles or outgassing
generated internally in normal operation. Very high humidity for
extended periods can corrode the heads and platters.

For giant magnetoresistive
(GMR) heads in particular, a minor head crash from contamination (that
does not remove the magnetic surface of the disk) still results in the
head temporarily overheating, due to friction with the disk surface,
and can render the data unreadable for a short period until the head
temperature stabilizes (so called "thermal asperity," a problem which
can partially be dealt with by proper electronic filtering of the read

hard disk's electronics control the movement of the actuator and the
rotation of the disk, and perform reads and writes on demand from the disk controller.
Modern disk firmware is capable of scheduling reads and writes
efficiently on the platter surfaces and remapping sectors of the media
which have failed.

Landing zones and load/unload technology

HDDs prevent power interruptions from shutting the drive down with its
heads landing in the data zone by either moving the heads to a landing zone or unloading (i.e., load/unload) the heads.

A landing zone
is an area of the platter usually near its inner diameter (ID), where
no data is stored. This area is called the Contact Start/Stop (CSS)
zone. Disks are designed such that either a spring or, more recently,
rotational inertia in the platters is used to park the heads in the case of unexpected power loss.

tension from the head mounting constantly pushes the heads towards the
platter. While the disk is spinning, the heads are supported by an air
bearing and experience no physical contact or wear. In CSS drives the
sliders carrying the head sensors (often also just called heads)
are designed to survive a number of landings and takeoffs from the
media surface, though wear and tear on these microscopic components
eventually takes its toll. Most manufacturers design the sliders to
survive 50,000 contact cycles before the chance of damage on startup
rises above 50%. However, the decay rate is not linear: when a disk is
younger and has had fewer start-stop cycles, it has a better chance of
surviving the next startup than an older, higher-mileage disk (as the
head literally drags along the disk's surface until the air bearing is
established). For example, the Seagate Barracuda 7200.10 series of
desktop hard disks are rated to 50,000 start-stop cycles. This means
that no failures attributed to the head-platter interface were seen
before at least 50,000 start-stop cycles during testing.

Around 1995 IBM pioneered a technology where a landing zone on the disk is made by a precision laser process (Laser Zone Texture = LZT) producing an array of smooth nanometer-scale "bumps" in a landing zone, thus vastly improving stiction
and wear performance. This technology is still largely in use today
(2007), predominantly in desktop and enterprise (3.5 inch) drives. In
general, CSS technology can be prone to increased stiction (the
tendency for the heads to stick to the platter surface), e.g. as a
consequence of increased humidity. Excessive stiction can cause
physical damage to the platter and slider or spindle motor.

technology relies on the heads being lifted off the platters into a
safe location, thus eliminating the risks of wear and stiction
altogether. The first HDD RAMAC and most early
disk drives used complex mechanisms to load and unload the heads.
Modern HDDs use ramp loading, first introduced by Memorex in 1967, to
load/unload onto plastic "ramps" near the outer disk edge.

HDDs today still use one of these two technologies. Each has a list of
advantages and drawbacks in terms of loss of storage area on the disk,
relative difficulty of mechanical tolerance control, cost of
implementation, etc.

Addressing shock robustness, IBM also created a technology for their ThinkPad line of laptop computers called the Active Protection System. When a sudden, sharp movement is detected by the built-in accelerometer
in the Thinkpad, internal hard disk heads automatically unload
themselves to reduce the risk of any potential data loss or scratch
defects. Apple later also utilized this technology in their PowerBook, iBook, MacBook Pro, and MacBook line, known as the Sudden Motion Sensor. Toshiba has released similar technology in their laptops.

Disk failures and their metrics

Most major hard disk and motherboard vendors now support self-monitoring, analysis and reporting technology (S.M.A.R.T.), which attempts to alert users to impending failures.

However, not all failures are predictable. Normal use eventually can lead to a breakd

in the inherently fragile device, which makes it essential for the user
to periodically back up the data onto a separate storage device.
Failure to do so can lead to the loss of data. While it may be possible
to recover lost information, it is normally an extremely costly
procedure, and it is not possible to guarantee success. A 2007 study
published by Google suggested very little
correlation between failure rates and either high temperature or
activity level. While several S.M.A.R.T. parameters have an impact on
failure probability, a large fraction of failed drives do not produce
predictive S.M.A.R.T. parameters. S.M.A.R.T. parameters alone may not
be useful for predicting individual drive failures.

SCSI, SAS and FC drives are typically more expensive and are traditionally used in servers and disk arrays, whereas inexpensive ATA and SATA drives evolved in the home computer market and were perceived to be less reliable. This distinction is now becoming blurred.

The mean time between failures (MTBF) of SATA drives is usually about 600,000 hours (some drives such as Western Digital Raptor
have rated 1.2 million hours MTBF), while SCSI drives are rated for
upwards of 1.5 million hours. However, independent research indicates
that MTBF is not a reliable estimate of a drive's longevity. MTBF is
conducted in laboratory environments in test chambers and is an
important metric to determine the quality of a disk drive b

efore it enters high volume production. Once the drive product is in production, the more valid metric is annualized failure rate (AFR). AFR is the percentage of real-world drive failures after shipping.

SAS drives are comparable to SCSI drives, with high MTBF and high reliability.

SATA drives designed and produced for enterprise markets, unlike
standard SATA drives, have reliability comparable to other enterprise
class drives.

enterprise drives (all enterprise drives, including SCSI, SAS,
enterprise SATA and FC) experience between .70%-.78% annual failure
rates from the total installed drives.
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PostSubject: Re: What is Hard disk drive?   Fri Aug 01, 2008 9:35 am


technological resources and know-how required for modern drive
development and production mean that as of 2007, over 98% of the
world's HDDs are manufactured by just a handful of large firms: Seagate
(which now owns Maxtor), Western Digital, Samsung, and Hitachi (which
owns the former disk manufacturing

division of IBM). Fujitsu continues to make mobile- and server-class
disks but exited the desktop-class market in 2001. Toshiba is a major
manufacturer of 2.5-inch and 1.8-inch notebook disks. ExcelStor is a
small HDD manufacturer.

Dozens of former HDD manufacturers have gone out of business, merged, or closed their HDD

as capacities and demand for products increased, profits became hard to
find, and the market underwent significant consolidation in the late
1980s and late 1990s. The first notable casualty of the business in the
PC era was Computer Memories Inc. or CMI; after an incident with faulty
20 MB AT disks in 1985, CMI's reputation never recovered, and they
exited the HDD business in 1987. Another notable failure was
MiniScribe, who went bankrupt in 1990 after it was found that they had
engaged in accounting fraud and inflated sales numbers for several
years. Many other smaller companies (like Kalok, Microscience, LaPine,
Areal, Priam and PrairieTek) also did not survive the shakeout, and had
disappeared by 1993; Micropolis was able to hold on until 1997, and
JTS, a relative latecomer to the scene, lasted only a few years and was
gone by 1999, after atte

to manufacture HDDs in India. Their claim to fame was creating a new 3"
form factor drive for use in laptops. Quantum and Integral also
invested in the 3" form factor; but eventually gave up as this form
factor failed to catch on. Rodime was also an important manufacturer
during the 1980s, but stopped making disks in the early 1990s amid the
shakeout and now concentrates on technology licensing; they hold a
number of patents related to 3.5-inch form factor HDDs.

* 1988:
Tandem Computers sold its disk manufacturing division to Western
Digital (WDC), which was then a well-known controller designer.
* 1989: Seagate Technology bought Control Data's high-end disk business, as part of CDC's exit from hardware manufacturing.
* 1990: Maxtor buys MiniScribe out of bankruptcy, making it the core of its low-end disk division.
* 1994: Quantum bought DEC's storage division, giving it a high-end disk range to go with its more consumer-oriented ProDrive range, as well as the DLT tape drive range.
* 1995:
Conner Peripherals, which was founded by one of Seagate Technology's
co-founders along with personnel from MiniScribe, announces a merger
with Seagate, which was completed in early 1996.
* 1996:
JTS merges with Atari, allowing JTS to bring its disk range into
production. Atari was sold to Hasbro in 1998, while JTS itself went
bankrupt in 1999.
* 2000: Quantum sells its disk division to Maxtor to concentrate on tape drives and backup equipment.
* 2003:
Following the controversy over mass failures of its Deskstar 75GXP
range, HDD pioneer IBM sold the majority of its disk division to
Hitachi, who renamed it Hitachi Global Storage Technologies (HGST).
* December
21, 2005: Seagate and Maxtor announced an agreement under which Seagate
would acquire Maxtor in an all stock transaction valued at $1.9
billion. The acquisition was approved by the appropriate regulatory
bodies, and closed on May 19, 2006.
* 2007

o April: Hitachi releases the 1 TB Hitachi Deskstar 7K1000 (1TB = 1 trillion bytes, roughly 931.5 GiB).
o July: Western Digital (WDC) acquires Komag U.S.A, a thin-film media manufacturer, for USD 1 Billion.
o September: Hitachi releases 2.5-inch 320 GB hard disk.

* 2008

o January:
Hitachi releases 2.5-inch 500 GB hard disk and it was demonstrated by
Asus with a laptop at 1 TB storage in CES event, Las Vegas


many years, HDDs were large, cumbersome devices, more suited to use in
the protected environment of a data center or large office than in a
harsh industrial environment (due to their delicacy), or small office
or home (due to their size and power consumption). Before the early
1980s, most HDDs had 8-inch (20 cm) or 14-inch (35 cm) platters,
required an equipment rack or a large amount of floor space (especially
the large removable-media disks, which were often referred to as
"washing machines"), and in many cases needed high-current or even
three-phase power hookups due to the large motors they used. Because of
this, HDDs were not commonly used with microcomputers until after 1980,
when Seagate Technology introduced the ST-506, the first 5.25-inch HDD, with a capacity of 5 megabytes. In fact, in its factory configuration, the original IBM PC (IBM 5150) was not equipped with a hard disk drive.

Most microcomputer HDDs in the early 1980s were not sold under their manufacturer's names, but by OEMs as part of larger peripherals (such as the Corvus Disk System and the Apple ProFile). The IBM PC/XT had an internal HDD, however, and this started a trend toward buying "bare" disks (often by mail order)
and installing them directly into a system. Hard disk drive makers
started marketing to end users as well as OEMs, and by the mid-1990s,
HDDs had become available on retail store shelves.

While internal disks became the system of choice on PCs, external HDDs remained popular for much longer on the Apple Macintosh
and other platforms. The first Apple Macintosh built between 1984 and
1986 had a closed architecture that did not support an external or
internal hard drive. In 1986, Apple added a SCSI port on the back, making external expansion easy. External SCSI drives were also popular with older microcomputers such as the Apple II series, and were also used extensively in servers, a usage which is still popular today. The appearance in the late 1990s of high-speed external interfaces such as USB and FireWire has made external disk systems popular among PC users once again, especially for laptop users, users who install Linux
in the additional external unit and users who move large amounts of
data between two or more areas. Most HDD makers now make their disks
available in external cases.
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What is Hard disk drive?
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