Download Report

Hard disk drive
“Hard drive” redirects here. For other uses, see Hard The primary characteristics of an HDD are its capacity
drive (disambiguation).
and performance. Capacity is speciﬁed in unit preﬁxes
A hard disk drive (HDD), hard disk, hard drive corresponding to powers of 1000: a 1-terabyte (TB) drive
has a capacity of 1,000 gigabytes (GB; where 1 gigabyte
= 1 billion bytes). Typically, some of an HDD’s capacity
is unavailable to the user because it is used by the ﬁle system and the computer operating system, and possibly inbuilt redundancy for error correction and recovery. Performance is speciﬁed by the time required to move the
heads to a track or cylinder (average access time) plus
the time it takes for the desired sector to move under the
head (average latency, which is a function of the physical
rotational speed in revolutions per minute), and ﬁnally the
speed at which the data is transmitted (data rate).
The two most common form factors for modern HDDs
are 3.5-inch, for desktop computers, and 2.5-inch, primarily for laptops. HDDs are connected to systems by
standard interface cables such as SATA (Serial ATA),
USB or SAS (Serial attached SCSI) cables.
A disassembled and labeled 1997 HDD lying atop a mirror
As of 2015, the primary competing technology for secondary storage is ﬂash memory in the form of solid-state
drives (SSDs), but HDDs remain the dominant medium
for secondary storage due to advantages in price per unit
of storage and recording capacity.[5][6] However, SSDs
are replacing HDDs where speed, power consumption
and durability are more important considerations.[7][8]
1 History
An overview of how HDDs work
or ﬁxed disk[lower-alpha 2] is a data storage device used
for storing and retrieving digital information using one
or more rigid (“hard”) rapidly rotating disks (platters)
coated with magnetic material. The platters are paired
with magnetic heads arranged on a moving actuator arm,
which read and write data to the platter surfaces.[2] Data
is accessed in a random-access manner, meaning that individual blocks of data can be stored or retrieved in any
order rather than sequentially. An HDD retains its data
even when powered oﬀ.
Introduced by IBM in 1956,[3] HDDs became the dominant secondary storage device for general-purpose computers by the early 1960s. Continuously improved, HDDs
have maintained this position into the modern era of
servers and personal computers. More than 200 companies have produced HDD units, though most current units Video of modern HDD operation (cover removed)
are manufactured by Seagate, Toshiba and Western Digital. Worldwide disk storage revenues were US $32 billion Main article: History of hard disk drives
in 2013, down 3% from 2012.[4]
1
2
HDDs were introduced in 1956 as data storage for an
IBM real-time transaction processing computer and were
developed for use with general-purpose mainframe and
minicomputers. The ﬁrst IBM drive, the 350 RAMAC,
was approximately the size of two refrigerators and stored
ﬁve million six-bit characters (3.75 megabytes)[9] on a
stack of 50 disks.
In 1962 IBM introduced the model 1311 disk drive,
which was about the size of a washing machine and
stored two million characters on a removable disk pack.
Users could buy additional packs and interchange them as
needed, much like reels of magnetic tape. Later models
of removable pack drives, from IBM and others, became
the norm in most computer installations and reached capacities of 300 megabytes by the early 1980s. Nonremovable HDDs were called “ﬁxed disk” drives.
2 TECHNOLOGY
ufacturer’s name such as the Apple ProFile. The IBM
PC/XT in 1983 included an internal 10 MB HDD, and
soon thereafter internal HDDs proliferated on personal
computers.
External HDDs remained popular for much longer on the
Apple Macintosh. Every Mac made between 1986 and
1998 has a SCSI port on the back, making external expansion easy; also, “toaster” Compact Macs did not have
easily accessible HDD bays (or, in the case of the Mac
Plus, any hard drive bay at all), so on those models, external SCSI disks were the only reasonable option.
The 2011 Thailand ﬂoods damaged manufacturing
plants, and impacted hard disk drive cost adversely in
2011-2013.[17]
Driven by ever increasing areal density since their invention, HDDs have continuously improved their characterSome high-performance HDDs were manufactured with istics; a few highlights are listed in the table above. At the
one head per track (e.g. IBM 2305) so that no time was same time, market application expanded from mainframe
lost physically moving the heads to a track.[15] Known as computers of the late 1950s to most mass storage appliﬁxed-head or head-per-track disk drives they were very cations including computers and consumer applications
expensive and are no longer in production.[16]
such as storage of entertainment content.
In 1973, IBM introduced a new type of HDD codenamed
“Winchester”. Its primary distinguishing feature was that
the disk heads were not withdrawn completely from the 2 Technology
stack of disk platters when the drive was powered down.
Instead, the heads were allowed to “land” on a special area
of the disk surface upon spin-down, “taking oﬀ” again
Magnetic Field lines
when the disk was later powered on. This greatly reread head
strong ﬁeld and ﬁeld reversal
near boundary
duced the cost of the head actuator mechanism, but precluded removing just the disks from the drive as was done
with the disk packs of the day. Instead, the ﬁrst models
of “Winchester technology” drives featured a removable
grain
magnetic region
disk module, which included both the disk pack and the
R = reverse
head assembly, leaving the actuator motor in the drive
R
N
R
R
N = no reverse
State:
0
1
Binary Value Encoded:
upon removal. Later “Winchester” drives abandoned the
removable media concept and returned to non-removable
platters.
Like the ﬁrst removable pack drive, the ﬁrst “Winchester”
drives used platters 14 inches (360 mm) in diameter. A
few years later, designers were exploring the possibility
that physically smaller platters might oﬀer advantages.
Drives with non-removable eight-inch platters appeared,
and then drives that used a 5 1 ⁄4 in (130 mm) form factor (a mounting width equivalent to that used by contemporary ﬂoppy disk drives). The latter were primarily
intended for the then-ﬂedgling personal computer (PC)
market.
As the 1980s began, HDDs were a rare and very expensive additional feature in PCs, but by the late 1980s their
cost had been reduced to the point where they were standard on all but the cheapest computers.
Most HDDs in the early 1980s were sold to PC end users
as an external, add-on subsystem. The subsystem was not
sold under the drive manufacturer’s name but under the
subsystem manufacturer’s name such as Corvus Systems
and Tallgrass Technologies, or under the PC system man-
Magnetic cross section & frequency modulation encoded binary
data
2.1 Magnetic recording
See also: Magnetic storage
An HDD records data by magnetizing a thin ﬁlm of
ferromagnetic material[lower-alpha 4] on a disk. Sequential
changes in the direction of magnetization represent binary data bits. The data is read from the disk by detecting the transitions in magnetization. User data is encoded using an encoding scheme, such as run-length limited encoding,[lower-alpha 5] which determines how the data
is represented by the magnetic transitions.
A typical HDD design consists of a spindle that holds
ﬂat circular disks, also called platters, which hold the
recorded data. The platters are made from a nonmagnetic material, usually aluminium alloy, glass, or ce-
2.2
Components
3
ramic, and are coated with a shallow layer of magnetic
material typically 10–20 nm in depth, with an outer
layer of carbon for protection.[19][20][21] For reference,
a standard piece of copy paper is 0.07–0.18 millimetres
(70,000–180,000 nm).[22]
Spindle
Platter
Head
Actuator Arm
Actuator Axis
Power Connector
Actuator
Jumper Block
IDE Connector
Diagram labeling the major components of a computer HDD
Recording of single magnetisations of bits on a 200 MB HDDplatter (recording made visible using CMOS-MagView).[23]
varying from 4,200 rpm in energy-eﬃcient portable devices, to 15,000 rpm for high-performance servers.[24]
The ﬁrst HDDs spun at 1,200 rpm[3] and, for many years,
3,600 rpm was the norm.[25] As of December 2013, the
platters in most consumer-grade HDDs spin at either
5,400 rpm or 7,200 rpm.
Information is written to and read from a platter as it rotates past devices called read-and-write heads that operate very close (often tens of nanometers) over the magnetic surface. The read-and-write head is used to detect
and modify the magnetization of the material immediately under it.
In modern drives 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 some older designs a stepper motor.
Early hard disk drives wrote data at some constant bits
per second, resulting in all tracks having the same amount
of data per track but modern drives (since the 1990s) use
zone bit recording—increasing the write speed from inner to outer zone and thereby storing more data per track
in the outer zones.
In modern drives, the small size of the magnetic regions creates the danger that their magnetic state might
be lost because of thermal eﬀects, thermally induced
magnetic instability which is commonly known as the
"superparamagnetic limit.” To counter this, the platters
are coated with two parallel magnetic layers, separated by
a 3-atom layer of the non-magnetic element ruthenium,
and the two layers are magnetized in opposite orientation, thus reinforcing each other.[26] Another technology
used to overcome thermal eﬀects to allow greater recording densities is perpendicular recording, ﬁrst shipped in
2005,[27] and as of 2007 the technology was used in many
HDDs.[28][29][30]
2.2 Components
A typical HDD has two electric motors; a spindle motor that spins the disks and an actuator (motor) that positions the read/write head assembly across the spinning
disks. The disk motor has an external rotor attached to
the disks; the stator windings are ﬁxed in place. Opposite the actuator at the end of the head support arm is the
read-write head; thin printed-circuit cables connect the
read-write heads to ampliﬁer electronics mounted at the
pivot of the actuator. The head support arm is very light,
but also stiﬀ; in modern drives, acceleration at the head
reaches 550 g.
The actuator is a permanent magnet and moving coil
motor that swings the heads to the desired position.
A metal plate supports a squat neodymium-iron-boron
The platters in contemporary HDDs are spun at speeds (NIB) high-ﬂux magnet. Beneath this plate is the movLongitudinal recording (standard) & perpendicular recording diagram
4
2 TECHNOLOGY
Currents along the top and bottom of the coil produce
radial forces that do not rotate the head.
HDD with disks and motor hub removed exposing copper colored
stator coils surrounding a bearing in the center of the spindle motor. Orange stripe along the side of the arm is thin printed-circuit
cable, spindle bearing is in the center and the actuator is in the
upper left
The HDD’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. Feedback of
the drive electronics is accomplished by means of special
segments of the disk dedicated to servo feedback. These
are either complete concentric circles (in the case of dedicated servo technology), or segments interspersed with
real data (in the case of embedded servo technology).
The servo feedback optimizes the signal to noise ratio of
the GMR sensors by adjusting the voice-coil of the actuated arm. The spinning of the disk also uses a servo motor. Modern disk ﬁrmware is capable of scheduling reads
and writes eﬃciently on the platter surfaces and remapping sectors of the media which have failed.
2.3 Error rates and handling
Modern drives make extensive use of error correction
codes (ECCs), particularly Reed–Solomon error correction. These techniques store extra bits, determined by
mathematical formulas, for each block of data; the extra
bits allow many errors to be corrected invisibly. The extra bits themselves take up space on the HDD, but allow
higher recording densities to be employed without causing uncorrectable errors, resulting in much larger storage
capacity.[31] For example, a typical 1 TB hard disk with
512-byte sectors provides additional capacity of about 93
GB for the ECC data.[32]
Head stack with an actuator coil on the left and read/write heads
on the right
ing coil, often referred to as the voice coil by analogy to
the coil in loudspeakers, which is attached to the actuator
hub, and beneath that is a second NIB magnet, mounted
on the bottom plate of the motor (some drives only have
one magnet).
The voice coil itself is shaped rather like an arrowhead,
and made of doubly coated copper magnet wire. The
inner layer is insulation, and the outer is thermoplastic,
which bonds the coil together after it is wound on a form,
making it self-supporting. The portions of the coil along
the two sides of the arrowhead (which point to the actuator bearing center) interact with the magnetic ﬁeld, developing a tangential force that rotates the actuator. Current
ﬂowing radially outward along one side of the arrowhead
and radially inward on the other produces the tangential
force. If the magnetic ﬁeld were uniform, each side would
generate opposing forces that would cancel each other
out. Therefore the surface of the magnet is half N pole,
half S pole, with the radial dividing line in the middle,
causing the two sides of the coil to see opposite magnetic
ﬁelds and produce forces that add instead of canceling.
In the newest drives, as of 2009, low-density parity-check
codes (LDPC) were supplanting Reed-Solomon; LDPC
codes enable performance close to the Shannon Limit and
thus provide the highest storage density available.[33]
Typical hard disk drives attempt to “remap” the data in
a physical sector that is failing to a spare physical sector
provided by the drive’s “spare sector pool” (also called
“reserve pool”),[34] while relying on the ECC to recover
stored data while the amount of errors in a bad sector
is still low enough. The S.M.A.R.T (Self-Monitoring,
Analysis and Reporting Technology) feature counts the
total number of errors in the entire HDD ﬁxed by ECC
(although not on all hard drives as the related S.M.A.R.T
attributes “Hardware ECC Recovered” and “Soft ECC
Correction” are not consistently supported), and the total
number of performed sector remappings, as the occurrence of many such errors may predict an HDD failure.
The “No-ID Format”, developed by IBM in the mid1990s, contains information about which sectors are bad
and where remapped sectors have been located.[35]
Only a tiny fraction of the detected errors ends up as not
correctable. For example, speciﬁcation for an enterprise
SAS disk (a model from 2013) estimates this fraction to
be one uncorrected error in every 1016 bits,[36] and another SAS enterprise disk from 2013 speciﬁes similar
5
error rates.[37] Another modern (as of 2013) enterprise
SATA disk speciﬁes an error rate of less than 10 nonrecoverable read errors in every 1016 bits.[38] An enterprise disk with a Fibre Channel interface, which uses 520
byte sectors to support the Data Integrity Field standard
to combat data corruption, speciﬁes similar error rates in
2005.[39]
The worst type of errors are those that go unnoticed, and
are not even detected by the disk ﬁrmware or the host
operating system. These errors are known as silent data
corruption, some of which may be caused by hard disk
drive malfunctions.[40]
2.4
Future development
Leading-edge hard disk drive areal densities from 1956 through
2009 compared to Moore’s law
HDD areal density's long term exponential growth has
been similar to a 41% per year Moore’s law rate; the
rate was 60–100% per year beginning in the early 1990s
and continuing until about 2005,[41][42] an increase which
Gordon Moore (1997) called “ﬂabbergasting” and he
speculated that HDDs had “moved at least as fast as
the semiconductor complexity.”[43] However, the rate decreased dramatically around 2006 and, during 2011–
2014, growth was in the annual range of 5–10%.[44] Disk
cost per byte improved nearly −45% per year during
1990–2010, and slowed after 2010 due to the Thailand
ﬂoods and diﬃculty in migrating from perpendicular
recording to newer technologies.[45][46][47] Moore (2005)
further observed that growth cannot continue forever.[48]
Increasing areal density corresponds to an ever decreasing
bit cell size. In 2013 a production desktop 3 TByte HDD
(4 platters) would have had an areal density of about 500
Gbit/in2 which would have amounted to a bit cell comprising about 18 magnetic grains (11 by 1.6 grains).[49]
Since the mid-2000s areal density progress has increasingly been challenged by a superparamagnetic trilemma
involving grain size, grain magnetic strength and ability
of the head to write.[50] In order to maintain acceptable
signal to noise smaller grains are required; smaller grains
may self-reverse (thermal instability) unless their magnetic strength is increased, but known write head mate-
rials are unable to generate a magnetic ﬁeld suﬃcient to
write the medium. Several new magnetic storage technologies are being developed to overcome or at least abate
this trilemma and thereby maintain the competitiveness
of HDDs with respect to products such as ﬂash memorybased solid-state drives (SSDs).
One such technology, shingled magnetic recording
(SMR), was introduced in 2013 by Seagate as “the ﬁrst
step to reaching a 20 TB HDD by 2020";[51] starting
from the 8 TB SMR hard disk drives available in 2015,
the pace of advancement would be 20% per year. Additionally, SMR comes with design complexities that
may cause reduced write performance.[52][53] Other new
recording technologies that, as of 2015, still remain under
development include heat-assisted magnetic recording
(HAMR),[54][55] microwave-assisted magnetic recording (MAMR),[56] two-dimensional magnetic recording
(TDMR),[49][57] bit-patterned recording (BPR),[58] and
“current perpendicular to plane” giant magnetoresistance
(CPP/GMR) heads.[59][60][61]
Depending upon assumptions on feasibility and timing
of these technologies, the median forecast by industry
observers and analysts for 2016 and beyond for areal
density growth is 20% per year with a range of 10%
to 40%.[49][62][63][64][65] The ultimate limit for the BPR
technology may be the superparamagnetic limit of a single particle that is estimated to be about two orders of
magnitude higher than the 500 Gbits/in2 density represented by 2013 production desktop HDDs.[49]
3 Capacity
The capacity of a hard disk drive, as reported by an operating system to the end user, is smaller than the amount
stated by a drive or system manufacturer; this can be
caused by a combination of factors: the operating system
using some space, diﬀerent units used while calculating
capacity, or data redundancy.
3.1 Calculation
Modern hard disk drives appear to their interface as a
contiguous set of logical blocks, so the gross drive capacity may be calculated by multiplying the number of
blocks by the block size. This information is available
from the manufacturer’s speciﬁcation and from the drive
itself through use of special utilities invoking low level
commands.[66][67]
The gross capacity of older HDDs may be calculated as
the product of the number of cylinders per zone, the
number of bytes per sector (most commonly 512), and
the count of zones of the drive. Some modern SATA
drives also report cylinder-head-sector (CHS) values, but
these are not actual physical parameters since the reported numbers are constrained by historic operating sys-
6
4 FORM FACTORS
tem interfaces. The C/H/S scheme has been replaced by
logical block addressing. In some cases, to try to “forceﬁt” the CHS scheme to large-capacity drives, the number
of heads was given as 64, although no modern drive has
anywhere near 32 platters: the typical 2 TB hard disk as
of 2013 has two 1 TB platters, and 4 TB drives use four
platters.
system and inodes in many UNIX ﬁle systems, as well
as other operating system data structures (also known as
metadata). As a consequence, not all the space on an
HDD is available for user ﬁles, but this system overhead
is usually negligible.
In modern HDDs, spare capacity for defect management 3.3 Units
is not included in the published capacity; however, in
many early HDDs a certain number of sectors were re- See also: Binary preﬁx § Disk drives
served as spares, thereby reducing the capacity available
to end users.
The total capacity of HDDs is given by manufactur[lower-alpha 9]
such as gigabytes (1
For RAID subsystems, data integrity and fault-tolerance ers in SI-based units
GB
=
1,000,000,000
bytes)
and
terabytes (1 TB =
requirements also reduce the realized capacity. For ex[72][74][75][76][77][78]
1,000,000,000,000
bytes).
The pracample, a RAID1 subsystem will be about half the total
tice
of
using
SI-based
preﬁxes
(denoting
powers
of 1,000)
capacity as a result of data mirroring. RAID5 subsystems
in
the
hard
disk
drive
and
computer
industries
dates
back
with x drives, would lose 1/x of capacity to parity. RAID
[79]
to
the
early
days
of
computing;
by
the
1970s,
“milsubsystems are multiple drives that appear to be one drive
used in the decor more drives to the user, but provides a great deal of lion”, “mega” and “M” were consistently
[80][81][82]
imal
sense
for
drive
capacity.
However,
capacifault-tolerance. Most RAID vendors use some form of
ties
of
memory
(RAM,
ROM)
and
CDs
are
traditionally
checksums to improve data integrity at the block level.
For many vendors, this involves using HDDs with sec- quoted using binary preﬁxes, meaning powers of 1,024.
tors of 520 bytes per sector to contain 512 bytes of user Computers internally do not represent either hard drive
data and eight checksum bytes or using separate 512-byte or memory capacity in powers of 1,024; reporting it in
sectors for the checksum data.[68]
this manner is a convention.[83] Microsoft Windows famIn some systems, there may be hidden partitions used for ily of operating systems uses the binary convention when
system recovery that reduce the capacity available to the reporting storage capacity, so a HDD oﬀered by its manufacturer as a 1 TB drive is reported by these operatend user.
ing systems as a 931 GB HDD. Mac OS X 10.6 ("Snow
Leopard") uses decimal convention when reporting HDD
capacity.[83]
3.2
System use
Main article: Disk formatting
The presentation of a hard disk drive to its host is determined by the disk controller. The actual presentation may
diﬀer substantially from the drive’s native interface, particularly in mainframes or servers. Modern HDDs, such
as SAS[66] and SATA[67] drives, appear at their interfaces
as a contiguous set of logical blocks that are typically 512
bytes long, though the industry is in the process of changing to the 4,096-byte logical blocks layout, known as the
Advanced Format (AF).[69]
The process of initializing these logical blocks on the
physical disk platters is called low-level formatting, which
is usually performed at the factory and is not normally
changed in the ﬁeld.[70][lower-alpha 6] As a next step in
preparing an HDD for use, high-level formatting writes
partition and ﬁle system structures into selected logical
blocks to make the remaining logical blocks available to
the host’s operating system and its applications.[71] The
ﬁle system uses some of the disk space to structure the
HDD and organize ﬁles, recording their ﬁle names and
the sequence of disk areas that represent the ﬁle. Examples of data structures stored on disk to retrieve ﬁles
include the File Allocation Table (FAT) in the DOS ﬁle
The diﬀerence between the decimal and binary preﬁx
interpretation caused some consumer confusion and led
to class action suits against HDD manufacturers. The
plaintiﬀs argued that the use of decimal preﬁxes effectively misled consumers while the defendants denied
any wrongdoing or liability, asserting that their marketing and advertising complied in all respects with the
law and that no class member sustained any damages or
injuries.[84][85][86]
4 Form factors
IBM’s ﬁrst hard drive, the IBM 350, used a stack of
ﬁfty 24-inch platters and was of a size comparable to
two large refrigerators. In 1962, IBM introduced its
model 1311 disk, which used six 14-inch (nominal size)
platters in a removable pack and was roughly the size
of a washing machine. This became a standard platter
size and drive form-factor for many years, used also by
other manufacturers.[99] The IBM 2314 used platters of
the same size in an eleven-high pack and introduced the
“drive in a drawer” layout, although the “drawer” was not
the complete drive.
Later drives were designed to ﬁt entirely into a chassis
7
mm × 203 mm). This smaller form factor, ﬁrst
used in an HDD by Seagate in 1980,[100] was the
same size as full-height 5 1 ⁄4 -inch-diameter (130
mm) FDD, 3.25-inches high. This is twice as high as
“half height"; i.e., 1.63 in (41.4 mm). 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 format was standardized
as EIA−741 and co-published as SFF−8501 for
disk drives, with other SFF-85xx series standards
covering related 5.25 inch devices (optical drives,
etc.)[101] 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 versions.
8-, 5.25-, 3.5-, 2.5-, 1.8- and 1-inch HDDs, together with a ruler
to show the length of platters and read-write heads
3.5-inch 4 in × 1 in × 5.75 in (101.6 mm × 25.4 mm
× 146 mm) = 376.77344 cm³. This smaller form
factor is similar to that used in an HDD by Rodime
in 1983,[102] which was the same size as the “half
height” 3½" FDD, i.e., 1.63 inches high. Today,
the 1-inch high (“slimline” or “low-proﬁle”) version
of this form factor is the most popular form used
in most desktops. The format was standardized in
terms of dimensions and positions of mounting holes
as EIA/ECA-740, co-published as SFF−8301.[103]
2.5-inch 2.75 in × 0.275–0.75 in × 3.945 in (69.85
mm × 7–19 mm × 100 mm) = 48.895–132.715
cm3 . This smaller form factor was introduced by
PrairieTek in 1988;[104] there is no corresponding
FDD. The 2.5-inch drive format is standardized
in the EIA/ECA-720 co-published as SFF−8201;
when used with speciﬁc connectors, more detailed
A modern 2.5-inch (63.5 mm) 6,495 MB HDD compared to an
speciﬁcations are SFF-8212 for the 50-pin (ATA
older 5.25-inch full-height 110 MB HDD
laptop) connector, SFF-8223 with the SATA, or
SAS connector and SFF-8222 with the SCA-2
that would mount in a 19-inch rack. Digital’s RK05 and
connector.[105]
RL01 were early examples using single 14-inch platters
in removable packs, the entire drive ﬁtting in a 10.5-inch- It came to be widely used for HDDs in mobile devices (laptops, music players, etc.) and for solidhigh rack space (six rack units). In the mid-to-late 1980s
state drives (SSDs), by 2008 replacing some 3.5
the similarly sized Fujitsu Eagle, which used (coincideninch enterprise-class drives.[106] It is also used in the
tally) 10.5-inch platters, was a popular product.
PlayStation 3[107] and Xbox 360 video game conSuch large platters were never used with microprocessorsoles.
based systems. With increasing sales of microcomputers having built in ﬂoppy-disk drives (FDDs), HDDs
Drives 9.5 mm high became an unoﬃcial standard for
that would ﬁt to the FDD mountings became desirable.
all except the largest-capacity laptop drives (usually
Thus HDD Form factors, initially followed those of 8having two platters inside); 12.5 mm-high drives,
inch, 5.25-inch, and 3.5-inch ﬂoppy disk drives. Because
typically with three platters, are used for maximum
there were no smaller ﬂoppy disk drives, smaller HDD
capacity, but will not ﬁt most laptop computers.
form factors developed from product oﬀerings or indusEnterprise-class drives can have a height up to 15
try standards.
mm.[108] Seagate released a 7 mm drive aimed at
entry level laptops and high end netbooks in December 2009.[109] Western Digital released on April 23,
8-inch 9.5 in × 4.624 in × 14.25 in (241.3 mm × 117.5
2013 a hard drive 5 mm in height speciﬁcally aimed
mm × 362 mm). In 1979, Shugart Associates'
at UltraBooks.[110]
SA1000 was the ﬁrst form factor compatible HDD,
having the same dimensions and a compatible inter1.8-inch 54 mm × 8 mm × 78.5 mm[lower-alpha 12] =
face to the 8” FDD.
33.912 cm³. This form factor, originally introduced
5.25-inch 5.75 in × 3.25 in × 8 in (146.1 mm × 82.55
by Integral Peripherals in 1993, evolved into the
8
5
ATA-7 LIF with dimensions as stated. For a time
it was increasingly used in digital audio players and
subnotebooks, but its popularity decreased to the
point where this form factor is increasingly rare and
only a small percentage of the overall market.[111]
There was an attempt to standardize this format as
SFF-8123, but it was cancelled in 2005.[112] SATA
revision 2.6 standardized the internal Micro SATA
connector and device dimensions.
PERFORMANCE CHARACTERISTICS
An HDD’s Average Access Time is its average seek time
which technically is the time to do all possible seeks divided by the number of all possible seeks, but in practice
is determined by statistical methods or simply approximated as the time of a seek over one-third of the number
of tracks.[119]
Defragmentation is a procedure used to minimize delay
in retrieving data by moving related items to physically
proximate areas on the disk.[120] Some computer operating systems perform defragmentation automatically. Although automatic defragmentation is intended to reduce
access delays, performance will be temporarily reduced
while the procedure is in progress.[121]
1-inch 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. Samsung calls the
same form factor “1.3 inch” drive in its product
literature.[113]
Time to access data can be improved by increasing rotational speed (thus reducing latency) or by reducing the
0.85-inch 24 mm × 5 mm × 32 mm. Toshiba antime spent seeking. Increasing areal density increases
nounced this form factor in January 2004[114] for
throughput by increasing data rate and by increasing the
use in mobile phones and similar applications, inamount of data under a set of heads, thereby potentially
cluding SD/MMC slot compatible HDDs optimized
reducing seek activity for a given amount of data. The
for video storage on 4G handsets. Toshiba mantime to access data has not kept up with throughput inufactured a 4 GB (MK4001MTD) and an 8 GB
creases, which themselves have not kept up with growth
(MK8003MTD) version and holds the Guinness
in bit density and storage capacity.
World Record for the smallest HDD.[115][116]
As of 2012, 2.5-inch and 3.5-inch hard disks were the 5.2
most popular sizes.
Seek time
By 2009 all manufacturers had discontinued the devel- See also: Hard disk drive performance characteristics:
opment of new products for the 1.3-inch, 1-inch and Seek time
0.85-inch form factors due to falling prices of ﬂash memory,[117][118] which has no moving parts.
Average seek time ranges from under 4 ms for high-end
While these sizes are customarily described by an approx- server drives[122] to 15 ms for mobile drives, with the most
imately correct ﬁgure in inches, actual sizes have long common mobile drives at about 12 ms[123] and the most
common desktop type typically being around 9 ms. The
been speciﬁed in millimeters.
ﬁrst HDD had an average seek time of about 600 ms;[3]
by the middle of 1970s HDDs were available with seek
times of about 25 ms.[124] Some early PC drives used a
5 Performance characteristics
stepper motor to move the heads, and as a result had seek
times as slow as 80–120 ms, but this was quickly imMain article: Hard disk drive performance characteristics proved by voice coil type actuation in the 1980s, reducing
seek times to around 20 ms. Seek time has continued to
improve slowly over time.
5.1
Time to access data
Some desktop and laptop computer systems allow the
user to make a tradeoﬀ between seek performance and
drive noise. Faster seek rates typically require more energy usage to quickly move the heads across the platter,
causing louder noises from the pivot bearing and greater
device vibrations as the heads are rapidly accelerated during the start of the seek motion and decelerated at the end
of the seek motion. Quiet operation reduces movement
speed and acceleration rates, but at a cost of reduced seek
performance.
The factors that limit the time to access the data on an
HDD are mostly related to the mechanical nature of the
rotating disks and moving heads. Seek time is a measure
of how long it takes the head assembly to travel to the
track of the disk that contains data. Rotational latency
is incurred because the desired disk sector may not be
directly under the head when data transfer is requested.
These two delays are on the order of milliseconds each.
The bit rate or data transfer rate (once the head is in the
right position) creates delay which is a function of the
number of blocks transferred; typically relatively small, 5.3 Latency
but can be quite long with the transfer of large contiguous
ﬁles. Delay may also occur if the drive disks are stopped Latency is the delay for the rotation of the disk to bring
the required disk sector under the read-write mechanism.
to save energy.
9
It depends on rotational speed of a disk, measured in
revolutions per minute (rpm). Average rotational latency
is shown in the table on the right, based on the statistical
relation that the average latency in milliseconds for such
a drive is one-half the rotational period.
5.4
Data transfer rate
As of 2010, a typical 7,200-rpm desktop HDD has a
sustained “disk-to-buﬀer" data transfer rate up to 1,030
Mbits/sec.[125] This rate depends on the track location;
the rate is higher for data on the outer tracks (where there
are more data sectors per rotation) and lower toward the
inner tracks (where there are fewer data sectors per rotation); and is generally somewhat higher for 10,000-rpm
drives. A current widely used standard for the “buﬀer-tocomputer” interface is 3.0 Gbit/s SATA, which can send
about 300 megabyte/s (10-bit encoding) from the buﬀer
to the computer, and thus is still comfortably ahead of
today’s disk-to-buﬀer transfer rates. Data transfer rate
(read/write) can be measured by writing a large ﬁle to
disk using special ﬁle generator tools, then reading back
the ﬁle. Transfer rate can be inﬂuenced by ﬁle system
fragmentation and the layout of the ﬁles.[120]
HDD data transfer rate depends upon the rotational speed
of the platters and the data recording density. Because
heat and vibration limit rotational speed, advancing density becomes the main method to improve sequential
transfer rates. Higher speeds require a more powerful
spindle motor, which creates more heat. While areal density advances by increasing both the number of tracks
across the disk and the number of sectors per track, only
the latter increases the data transfer rate for a given rpm.
Since data transfer rate performance only tracks one of
the two components of areal density, its performance improves at a lower rate.
Inner view of a 1998 Seagate HDD that used Parallel ATA interface
2.5-inch SATA drive on top of a 3.5-inch SATA drive, close-up
of data and power connectors
of the computer, no matter what data encoding scheme
is used internally. Typically a DSP in the electronics inside the HDD takes the raw analog voltages from the read
head and uses PRML and Reed–Solomon error correction[126] to decode the sector boundaries and sector data,
then sends that data out the standard interface. That DSP
also watches the error rate detected by error detection
and correction, and performs bad sector remapping, data
collection for Self-Monitoring, Analysis, and Reporting
Technology, and other internal tasks.
Modern interfaces connect an HDD to a host bus interface adapter (today typically integrated into the "south
bridge") with one data/control cable. Each drive also has
5.5 Other considerations
an additional power cable, usually direct to the power supOther performance considerations include power con- ply unit.
sumption, audible noise, and shock resistance.
6
Access and interfaces
Main article: Hard disk drive interface
HDDs are accessed over one of a number of bus types,
including as of 2011 parallel ATA (PATA, also called
IDE or EIDE; described before the introduction of SATA
as ATA), Serial ATA (SATA), SCSI, Serial Attached
SCSI (SAS), and Fibre Channel. Bridge circuitry is
sometimes used to connect HDDs to buses with which
they cannot communicate natively, such as IEEE 1394,
USB and SCSI.
Modern HDDs present a consistent interface to the rest
• Small Computer System Interface (SCSI), originally named SASI for Shugart Associates System
Interface, was standard on servers, workstations,
Commodore Amiga, Atari ST and Apple Macintosh
computers through the mid-1990s, by which time
most models had been transitioned to IDE (and later,
SATA) family disks. The range limitations of the
data cable allows for external SCSI devices.
• Integrated Drive Electronics (IDE), later standardized under the name AT Attachment (ATA, with
the alias P-ATA or PATA (Parallel ATA) retroactively added upon introduction of SATA) moved the
HDD controller from the interface card to the disk
drive. This helped to standardize the host/controller
10
7
interface, reduce the programming complexity in
the host device driver, and reduced system cost and
complexity. The 40-pin IDE/ATA connection transfers 16 bits of data at a time on the data cable.
The data cable was originally 40-conductor, but later
higher speed requirements for data transfer to and
from the HDD led to an “ultra DMA” mode, known
as UDMA. Progressively swifter versions of this
standard ultimately added the requirement for an 80conductor variant of the same cable, where half of
the conductors provides grounding necessary for enhanced high-speed signal quality by reducing cross
talk.
INTEGRITY AND FAILURE
7 Integrity and failure
• EIDE was an unoﬃcial update (by Western Digital)
to the original IDE standard, with the key improvement being the use of direct memory access (DMA)
to transfer data between the disk and the computer
without the involvement of the CPU, an improvement later adopted by the oﬃcial ATA standards.
Close-up of an HDD head resting on a disk platter; its mirror
By directly transferring data between memory and reﬂection is visible on the platter surface.
disk, DMA eliminates the need for the CPU to copy
byte per byte, therefore allowing it to process other Main articles: Hard disk drive failure and Data recovery
tasks while the data transfer occurs.
• Fibre Channel (FC) is a successor to parallel SCSI
interface on enterprise market. It is a serial protocol.
In disk drives usually the Fibre Channel Arbitrated
Loop (FC-AL) connection topology is used. FC has
much broader usage than mere disk interfaces, and it
is the cornerstone of storage area networks (SANs).
Recently other protocols for this ﬁeld, like iSCSI
and ATA over Ethernet have been developed as well.
Confusingly, drives usually use copper twisted-pair
cables for Fibre Channel, not ﬁbre optics. The latter
are traditionally reserved for larger devices, such as
servers or disk array controllers.
• Serial Attached SCSI (SAS). The SAS is a new generation serial communication protocol for devices
designed to allow for much higher speed data transfers and is compatible with SATA. SAS uses a mechanically identical data and power connector to
standard 3.5-inch SATA1/SATA2 HDDs, and many
server-oriented SAS RAID controllers are also capable of addressing SATA HDDs. SAS uses serial
communication instead of the parallel method found
in traditional SCSI devices but still uses SCSI commands.
• Serial ATA (SATA). The SATA data cable has one
data pair for diﬀerential transmission of data to the
device, and one pair for diﬀerential receiving from
the device, just like EIA-422. That requires that
data be transmitted serially. A similar diﬀerential
signaling system is used in RS485, LocalTalk, USB,
FireWire, and diﬀerential SCSI.
Due to the extremely close spacing between the heads and
the disk surface, HDDs are vulnerable to being damaged
by 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, contamination of the drive’s internal
enclosure, wear and tear, corrosion, or poorly manufactured platters and heads.
The HDD’s spindle system relies on air density inside the
disk enclosure to support the heads at their proper ﬂying height while the disk rotates. HDDs require a certain range of air densities in order to operate properly.
The connection to the external environment and density
occurs through a small hole in the enclosure (about 0.5
mm in breadth), usually with a ﬁlter on the inside (the
breather ﬁlter).[127] If the air density 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 (9,800 ft).[128] Modern disks
include temperature sensors and adjust their operation to
the operating environment. Breather holes can be seen on
all disk drives—they usually have a sticker next to them,
warning the user not to cover the holes. The air inside
the operating drive 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 humid-
11
ity present for extended periods of time can corrode the
heads and platters.
8 Market segments
For giant magnetoresistive (GMR) heads in particular, Desktop HDDs They typically store between 60 GB and
4 TB and rotate at 5,400 to 10,000 rpm, and have a
a minor head crash from contamination (that does not
media transfer rate of 0.5 Gbit/s or higher (1 GB
remove the magnetic surface of the disk) still results in
= 109 bytes; 1 Gbit/s = 109 bit/s). As of August
the head temporarily overheating, due to friction with
2014, the highest-capacity desktop HDDs store 8
the disk surface, and can render the data unreadable for
TB.[87][133]
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 sigMobile (laptop) HDDs
nal).
When the logic board of a hard disk fails, the drive can
often be restored to functioning order and the data recovered by replacing the circuit board of one of an identical
hard disk. In the case of read-write head faults, they can
be replaced using specialized tools in a dust-free environment. If the disk platters are undamaged, they can be
transferred into an identical enclosure and the data can
be copied or cloned onto a new drive. In the event of
disk-platter failures, disassembly and imaging of the disk
platters may be required.[129] For logical damage to ﬁle
systems, a variety of tools, including fsck on UNIX-like
systems and CHKDSK on Windows, can be used for data
recovery. Recovery from logical damage can require ﬁle Two enterprise-grade SATA 2.5-inch 10,000 rpm HDDs,
factory-mounted in 3.5-inch adapter frames
carving.
A common expectation is that hard disk drives designed
for server use will fail less frequently than consumergrade drives usually used in desktop computers. A study
by Carnegie Mellon University[130] and an independent
one by Google[131] both found that the “grade” of a drive
does not relate to the drive’s failure rate.
A 2011 summary of research into SSD and magnetic disk
failure patterns by Tom’s Hardware summarized research
ﬁndings as follows:[132]
• MTBF does not indicate reliability; the annualized
failure rate is higher and usually more relevant.
Smaller than their desktop and enterprise counterparts, they tend to be slower and have lower capacity. Mobile HDDs spin at 4,200 rpm, 5,200 rpm,
5,400 rpm, or 7,200 rpm, with 5,400 rpm being typical. 7,200 rpm drives tend to be more expensive
and have smaller capacities, while 4,200 rpm models usually have very high storage capacities. Because of smaller platter(s), mobile HDDs generally
have lower capacity than their greater desktop counterparts.
There are also 2.5-inch drives spinning at 10,000 rpm,
which belong to the enterprise segment with no intention to be used in laptops.
• Magnetic disks do not have a speciﬁc tendency to fail
during early use, and temperature only has a minor Enterprise HDDs Typically used with multiple-user
computers running enterprise software. Examples
eﬀect; instead, failure rates steadily increase with
are: transaction processing databases, internet inage.
frastructure (email, webserver, e-commerce), scientiﬁc computing software, and nearline storage man• S.M.A.R.T. warns of mechanical issues but not
agement software. Enterprise drives commonly opother issues aﬀecting reliability, and is therefore not
erate continuously (“24/7”) in demanding environa reliable indicator of condition.
ments while delivering the highest possible performance without sacriﬁcing reliability. Maximum capacity is not the primary goal, and as a result the
• Failure rates of drives sold as “enterprise” and
drives are often oﬀered in capacities that are rela“consumer” are “very much similar”, although custively low in relation to their cost.[134]
tomized for their diﬀerent environments.
• In drive arrays, one drive’s failure signiﬁcantly increases the short-term chance of a second drive failing.
The fastest enterprise HDDs spin at 10,000 or 15,000
rpm, and can achieve sequential media transfer
speeds above 1.6 Gbit/s[135] and a sustained transfer rate up to 1 Gbit/s.[135] Drives running at 10,000
12
10 EXTERNAL HARD DISK DRIVES
or 15,000 rpm use smaller platters to mitigate increased power requirements (as they have less air
drag) and therefore generally have lower capacity
than the highest capacity desktop drives. Enterprise
HDDs are commonly connected through Serial Attached SCSI (SAS) or Fibre Channel (FC). Some
support multiple ports, so they can be connected to
a redundant host bus adapter.
Worldwide revenues for disk storage were $32 billion in
2013, down about 3% from 2012.[4] This corresponds to
shipments of 552 million units in 2013 compared to 578
million in 2012 and 622 million in 2011.[4] The estimated
2013 market shares are about 40–45% each for Seagate
and Western Digital and 13–16% for Toshiba.
Enterprise HDDs can have sector sizes larger than 512 10 External hard disk drives
bytes (often 520, 524, 528 or 536 bytes). The additional per-sector space can be used by hardware
RAID controllers or applications for storing Data See also: USB mass storage / USB drive and Disk
Integrity Field (DIF) or Data Integrity Extensions enclosure
(DIX) data, resulting in higher reliability and prevention of silent data corruption.[136]
Consumer electronics HDDs They include drives embedded into digital video recorders and automotive
vehicles. The former are conﬁgured to provide a
guaranteed streaming capacity, even in the face of
read and write errors, while the latter are built to resist larger amounts of shock.
9
Toshiba 1 TB 2.5” external USB 2.0 hard disk drive
Manufacturers and sales
20
02
IBM
Hitachi
Fujitsu
20
11
2.5
"
09
20
12
20 "
5
3.
Toshiba
WD
Seagate
1989
Tandon
88
19
1
96
Samsung
19
06
20
Conner
3.0 TB 3.5” Seagate FreeAgent GoFlex plug and play
external USB 3.0-compatible drive (left), 750 GB 3.5”
Seagate Technology push-button external USB 2.0 drive
(right), and a 500 GB 2.5” generic brand plug and play
external USB 2.0 drive (front).
201
CDC
0
0
20
19
90
Maxtor
MiniScribe
19
Diagram of HDD manufacturer consolidation
94
Plus
19
92
Quantum
DEC
External hard disk drives[lower-alpha 14] typically connect
via USB; variants using USB 2.0 interface generally have
slower data transfer rates when compared to internally
mounted hard drives connected through SATA. Plug and
play drive functionality oﬀers system compatibility and
features large storage options and portable design. As of
January 2015, available capacities for external hard disk
drives range from 500 GB to 6 TB.
See also: History of hard disk drives and List of defunct External hard disk drives are usually available as prehard disk manufacturers
assembled integrated products, but may be also assembled by combining an external enclosure (with USB
More than 200 companies have manufactured HDDs over or other interface) with a separately purchased drive.
time. But consolidations have concentrated production They are available in 2.5-inch and 3.5-inch sizes; 2.5into just three manufacturers today: Western Digital, inch variants are typically called portable external drives,
Seagate, and Toshiba.
while 3.5-inch variants are referred to as desktop exter-
13
nal drives. “Portable” drives are packaged in smaller and
lighter enclosures than the “desktop” drives; additionally,
“portable” drives use power provided by the USB connection, while “desktop” drives require external power
bricks.
Features such as biometric security or multiple interfaces
(for example, Firewire) are available at a higher cost.[137]
There are pre-assembled external hard disk drives that,
when taken out from their enclosures, cannot be used internally in a laptop or desktop computer due to embedded
USB interface on their printed circuit boards, and lack of
SATA (or Parallel ATA) interfaces.[138][139]
11
Visual representation
Hard disk drives are traditionally symbolized as a stylized stack of platters or as a cylinder, and are as such
found in various diagrams; sometimes, they are depicted
with small lights to indicate data access. In most modern
graphical user environments (GUIs), hard disk drives are
represented by an illustration or photograph of the drive
enclosure.
13 Notes
[1] This is the original ﬁling date of the application which led
to US Patent 3,503,060, generally accepted as the deﬁnitive disk drive patent.[1]
[2] Further terms used to describe hard disk drives include
disk drive, disk ﬁle, direct access storage device (DASD),
CKD disk, and Winchester disk drive (after the IBM 3340).
The term “DASD” includes other devices beside disks.
[3] Comparable in size to a large side-by-side refrigerator.
[4] Initially gamma iron oxide particles in an epoxy binder,
the recording layer in a modern HDD typically is domains
of a granular Cobalt-Chrome-Platinum based alloy physically isolated by an oxide to enable perpendicular recording.[18]
[5] Historically a variety of run-length limited codes have
been used in magnetic recording including for example,
codes named FM, MFM and GCR which are no longer
used in modern HDDs.
[6] However, some enterprise SAS drives have other block
sizes such as 520, 524 and 528 bytes, which can be
changed in the ﬁeld.
[7] Expressed using decimal multiples.
• In GUIs, hard disk drives are commonly symbolized
with a drive icon
• Two cylinders in a RAID diagram, symbolizing an
array of disks
12
See also
[8] Expressed using binary multiples.
[9] The International System of Units (SI), formerly known as
the “metric system”, does not deﬁne units for digital information but notes that the SI-deﬁned preﬁxes (such as kilo,
mega, etc.) may be applied outside the contexts where
SI-deﬁned base units or derived units would be used.
[10] Five platters for a conventional hard disk drive, and seven
platters for a hard disk drive ﬁlled with Helium.
[11] Most common.
• Automatic acoustic management
• Cleanroom
• Click of death
• Data erasure
• Drive mapping
[12] This dimension includes a 0.5 mm protrusion of the Micro
SATA connector from the device body.
[13] The Quantum Bigfoot TS used a maximum of three platters, other earlier and lower capacity product used up to
four platters in a 5.25-inch HH form factor, e.g., Microscience HH1090 circa 1989.
[14] These diﬀer from removable disk media, e.g., disk packs
or data modules, in that they include, for example, actuators, drive electronics, motors.
• Hybrid drive
• Microdrive
14 References
• RAID
[1] Kean, David W., “IBM San Jose, A quarter century of
innovation”, 1977.
• S.M.A.R.T.
[2] Arpaci-Dusseau, Remzi H.; Arpaci-Dusseau, Andrea C.
(2014). “Operating Systems: Three Easy Pieces [Chapter: Hard Disk Drives]". Arpaci-Dusseau Books.
• Solid-state drive
• Write precompensation
[3] “IBM Archives: IBM 350 disk storage unit”. Retrieved
2012-10-19.
14
14
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[4] IDC report: Worldwide Disk Storage Systems Quarterly
Tracker (2014-06-19). “Any Future for Worldwide Storage Industry?" (Press release). StorageNewsletter.com.
IDC. Retrieved 2014-07-14. Worldwide global disk storage systems revenue 2012 = $32,564 million; 2013 =
$31,688 million
[24] Blount, Walker C. (November 2007). “Why 7,200 RPM
Mobile Hard Disk Drives?". Archived from the original
on 2012-04-19. Retrieved 17 July 2011.
[5] Fullerton, Eric (March 2014). “5th Non-Volatile Memories Workshop (NVMW 2014)". IEEE. Retrieved April
23, 2014.
[26] Hayes, Brian. “Terabyte Territory”. Vol 90 (No 3 (May–
June 2002)). American Scientist. p. 212.
[6] Handy, James (July 31, 2012). “For the Lack of a Fab...”.
Objective Analysis. Retrieved November 25, 2012.
[7] Hutchinson, Lee. (2012-06-25) How SSDs conquered
mobile devices and modern OSes. Ars Technica. Retrieved on 2013-01-07.
[8] Santo Domingo, Joel (May 10, 2012). “SSD vs HDD:
What’s the Diﬀerence?". PC Magazine. Retrieved
November 24, 2012.
[9] “Time Capsule, 1956 Hard Disk”. Oracle Magazine. Oracle. July 2014. Retrieved September 19, 2014. IBM 350
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[10] “Toshiba Storage Solutions – MK3233GSG”.
[11] Ballistic Research Laboratories “A THIRD SURVEY OF
DOMESTIC ELECTRONIC DIGITAL COMPUTING
SYSTEMS,” March 1961, section on IBM 305 RAMAC
(p. 314-331) states a $34,500 purchase price which calculates to $9,200/MB.
[25] “Ref — Hard Disk Spindle Motor”. PC Guide. Retrieved
2013-01-07.
[27] “Press Releases December 14, 2004”. Toshiba. Retrieved
13 March 2009.
[28] “Seagate Momentus 2½" HDDs per webpage January
2008”. Seagate.com. 24 October 2008. Retrieved 13
March 2009.
[29] “Seagate Barracuda 3½" HDDs per webpage January
2008”. Seagate.com. Retrieved 13 March 2009.
[30] “Western Digital Scorpio 2½" and Greenpower 3½"
HDDs per quarterly conference, July 2007”. Wdc.com.
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[31] Error Correcting Code, The PC Guide
[32] Curtis E. Stevens (2011). “Advanced Format in Legacy
Infrastructures: More Transparent than Disruptive”
(PDF). idema.org. Retrieved 2013-11-05.
[33] “Iterative Detection Read Channel Technology in Hard
Disk Drives”, Hitachi
[12] “Farming hard drives: 2 years and $1M later”. Backblaze
Blog - The Life of a Cloud Backup Company.
[34] MjM Data Recovery Ltd. “MJM Data Recovery Ltd:
Hard Disk Bad Sector Mapping Techniques”. Datarecovery.mjm.co.uk. Archived from the original on 2014-0201. Retrieved 2014-01-21.
[13] “Magnetic head development”. IBM Archives. Retrieved
August 11, 2014.
[35] Charles M. Kozierok. “The PC Guide: Hard Disk: Sector
Format and Structure”. 1997–2004.
[14] “Seagate ST5000DM000 Desktop HDD Product Manual”. Seagate. Retrieved August 11, 2014.
[36] “Enterprise Performance 15K HDD: Data Sheet” (PDF).
Seagate. 2013. Retrieved 2013-10-24.
[15] Microsoft Windows NT Workstation 4.0 Resource Guide
1995, Chapter 17 – Disk and File System Basics
[37] “WD Xe: Datacenter hard drives” (PDF). Western Digital. 2013. Retrieved 2013-10-24.
[16] Computer Organization and Design, 2nd Ed., P. Pal
Chaudhuri, 2006,p. 635
[38] “WD Re: Datacenter Capacity HDD” (PDF). Western
Digital. 2013. Retrieved 2013-11-14.
[17] “Farming hard drives: how Backblaze weathered the
Thailand drive crisis”. blaze.com. 2013. Retrieved 201405-23.
[39] “Cheetah 10K.7 FC Product Manual”. Seagate. August
5, 2005. Archived from the original on June 12, 2009.
Retrieved August 29, 2013.
[18] New Paradigms in Magnetic Recording
[19] “Hard Drives”. escotal.com. Retrieved 16 July 2011.
[40] David S. H. Rosenthal (October 1, 2010). “Keeping Bits
Safe: How Hard Can It Be?". ACM Queue. Retrieved
2014-01-02.
[20] “What is a “head-crash” & how can it result in permanent
loss of my hard drive data?". data-master.com. Retrieved
16 July 2011.
[41] Whyte, Barry (September 18, 2009). “A brief History of
Areal Density]". IBM DeveloperWorks. Retrieved July 25,
2014.
[21] “Hard Drive Help”. hardrivehelp.com. Retrieved 16 July
2011.
[42] Walter, Chip (August 2005). “Kryder’s Law”. Scientiﬁc
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[22] Elert, Glenn. “Thickness of a Piece of Paper”. HyperTextbook.com. Retrieved 9 July 2011.
[43] “Gallium Arsenide”. PC Magazine. March 25, 1997. Retrieved August 16, 2014. Gordon Moore: ... the ability of
the magnetic disk people to continue to increase the density is ﬂabbergasting--that has moved at least as fast as the
semiconductor complexity.
[23] CMOS-MagView is an instrument that visualizes magnetic ﬁeld structures and strengths.
15
[44] Coughlin, Tom (2014-12-22). “HDD Areal Density And
$/TB Trends”. Coughlin Associates www.tomcoughlin.
com (Atascadero, CA: Forbes). Retrieved 2014-12-23.
graph is 5%/yr for 2011–2014. Current HDD areal density growth trends are in the range of 10% annually.
[54] “Xyratex no-go for bit-patterned media”. The Register.
24 April 2010. Retrieved 21 August 2010.
[45] Mellor, Chris (2014-11-10). “Kryder’s law craps out:
Race to UBER-CHEAP STORAGE is OVER”. theregister.co.uk (UK: The Register). Retrieved 2014-11-12. The
2011 Thai ﬂoods almost doubled disk capacity cost/GB
for a while. Rosenthal writes: “The technical diﬃculties
of migrating from PMR to HAMR, meant that already
in 2010 the Kryder rate had slowed signiﬁcantly and was
not expected to return to its trend in the near future. The
ﬂoods reinforced this.”
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0-201-59616-4.
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[128] “Ruggedized Disk Drives for Commercial Airborne Computer Systems”.
16 External links
• Computer History Museum’s HDD Working Group
Website
• Hard Disk Drives Encyclopedia
• Video showing an opened HD working
[129] Grabianowski, Ed. “How To Recover Lost Data from
Your Hard Drive”. HowStuﬀWorks. pp. 5–6. Retrieved
24 October 2012.
• Average seek time of a computer disk
[130] “Everything You Know About Disks Is Wrong”. Storagemojo.com. 2007-02-22. Retrieved 2010-08-24.
• HDD from inside: Tracks and Zones. How hard it
can be?
• Timeline: 50 Years of Hard Drives
18
• Hard disk hacking (ﬁrmware modiﬁcations, in eight
parts, going as far as booting a Linux kernel on an
ordinary HDD controller board)
• Hiding Data in Hard Drive’s Service Areas, February 14, 2013, by Ariel Berkman
16
EXTERNAL LINKS
19
17
17.1
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Text
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20
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17.2
Images
• File:2.5-inch_SATA_drive_on_top_of_a_3.5-inch_SATA_drive,_close-up_of_data_and_power_connectors.jpg
Source:
http://upload.wikimedia.org/wikipedia/commons/8/89/2.5-inch_SATA_drive_on_top_of_a_3.5-inch_SATA_drive%2C_close-up_
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17.3
Content license
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• File:Full_History_Disk_Areal_Density_Trend.png Source:
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• File:HardDisk1.ogg Source: http://upload.wikimedia.org/wikipedia/commons/c/cf/HardDisk1.ogg License: CC BY 3.0 Contributors:
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• File:HardDiskAnatomy.jpg Source: http://upload.wikimedia.org/wikipedia/commons/3/3b/HardDiskAnatomy.jpg License: Public domain Contributors: Transferred from en.wikipedia Original artist: Original uploader was Ben pcc at en.wikipedia
• File:Hard_disk_dismantled.jpg Source: http://upload.wikimedia.org/wikipedia/commons/1/1e/Hard_disk_dismantled.jpg License:
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• File:Hard_disk_head.jpg Source: http://upload.wikimedia.org/wikipedia/commons/7/75/Hard_disk_head.jpg License: CC BY 2.0 Contributors: ? Original artist: ?
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Contributors: Own work, based on the public domain image Image:Hdd od srodka.jpg. Image renamed from Image:Hard drive.svg Original
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• File:Harddrive-engineerguy.ogv Source: http://upload.wikimedia.org/wikipedia/commons/f/f8/Harddrive-engineerguy.ogv License:
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• File:MagneticMedia.svg Source: http://upload.wikimedia.org/wikipedia/commons/f/f3/MagneticMedia.svg License: CC BY-SA 3.0
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• File:Seagate_ST33232A_hard_disk_inner_view.jpg Source:
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• File:Toshiba_1_TB_External_USB_Hard_Drive.jpg Source: http://upload.wikimedia.org/wikipedia/commons/9/91/Toshiba_1_TB_
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• File:Two_Western_Digital_VelociRaptor_1_TB_SATA_10,000_rpm_3.5-inch_HDDs.jpg Source: http://upload.wikimedia.org/
wikipedia/commons/3/38/Two_Western_Digital_VelociRaptor_1_TB_SATA_10%2C000_rpm_3.5-inch_HDDs.jpg License: CC BYSA 4.0 Contributors: Own work Original artist: Dsimic
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