Hard Disk Drive
Hard Disk(English:Hard DiskDrive,abbreviation:HDD,sometimes called"mechanical hard
disk"or"traditional hard disk"in order to distinguish it from solid-state hard drives)is a
non-volatile memory based on hard rotating disks used on computers.It stores and stores on a
flat magnetic surface.To retrieve digital data,the data is written to the disk through the
magnetic head that is close to the magnetic surface and the polarity is changed by
electromagnetic current.The data can be read through the disk.The principle is that the disk
itself is when the head passes over the disk.The magnetic field causes the electrical signal in
the reading coil to change.Hard disk reads and writes adopt a semi-random access method,which
can read the data in the hard disk in any order,but the speed of reading data at different
locations is different.The hard disk consists of one or several high-speed rotating disks and a
magnetic head placed on the actuator cantilever.
Early hard disk storage media are replaceable,but now hard disk storage media generally cannot be
replaced.The disc and the magnetic head are sealed together in the hard drive.The hard disk has
an air hole with filtering measures to balance the pressure difference between the inside and
outside of the hard disk caused by the heat generated during work.
The hard disk was used by IBM in 1956 and became the main auxiliary storage
device(English:secondary storage)in general-purpose computers in the early 1960s.With the
advancement of technology,hard disks have also become the main components of servers and
According to different data interfaces,hard disks are roughly divided into ATA(also known as
IDE)and SATA,as well as SCSI and SAS.The interface speed is not the data transmission speed of
the actual hard disk.At present,the actual data transmission speed of an ordinary hard disk
generally does not exceed 300MB/s.
Full name Advanced TechnologyAttachment uses a traditional 40-pin parallel port data cable to
connect the motherboard and the hard disk.The maximum interface speed is 133MB/s.Because the
anti-interference of the parallel port cable is too poor,and the cable takes up a lot of
space,it is not good for the internal heat dissipation of the computer.Gradually replaced by
The full name is SerialATA,that is,the ATA interface that uses the serial port.It is
characterized by strong anti-interference,much lower requirements for data lines than ATA,and
supports hot plugging and other functions.The interface speed of SATA-II is 300MiB/s,and the new
SATA-III standard can reach a transfer speed of 600MiB/s.The data cable of SATA is also much
thinner than that of ATA,which is conducive to the air circulation in the case,and it is more
convenient to arrange the cables.
Full name Small Computer System Interface(minicomputer system interface),has experienced multiple
generations of development,from the early SCSI-II to the current Ultra320SCSI and
Fiber-Channel(fiber channel),the interface types are also diverse.SCSI hard disks are widely
used in workstation-class personal computers and servers.Therefore,more advanced technologies
are used,such as high-speed disk rotation of 15000rpm,and lower CPU usage during data
transmission,but the unit price is also higher than that of ATA and SATA of the same
capacity.Hard drives are more expensive.
Full name Serial AttachedSCSI is a new generation of SCSI technology,compatible with SATA hard
disks,and also supports hot-swappable.It adopts serial technology to obtain higher transmission
speed,which can reach 12Gb/s,and the disk rotation speed is also faster.The smaller connecting
line can improve the air circulation in the internal space of the system.Usually used in
enterprise products such as servers.In addition,because SAS hard disks can share the same
backplane with SATA hard disks,SATA hard disks can be used to replace some expensive SAS hard
disks in the same SAS storage system,saving overall storage costs.However,SATA storage systems
cannot connect to SAS hard drives.
The full name is FibreChannel(Fibre Channel Interface).The hard disk with this interface has the
characteristics of hot pluggability,high-speed bandwidth(4Gb/s or 10Gb/s),remote
connection,etc.when using optical fiber connection;the internal transmission rate is also higher
than ordinary The hard drive is higher.But its price is high,so FC interface is usually only
used in high-end server field.
3.5-inch desktop hard drives:ATA interface hard drives generally use a D-shaped 4-pin power
interface(commonly known as"big 4pin"),designed and patented by Molex;SATA hard drives use SATA
The 2.5-inch laptop hard drive can be directly powered by the data port,without the need for an
additional power interface.After the external portable hard disk box is plugged in,the external
USB interface of the computer provides the power source,and a single USB interface power supply
is about 4~5V500mA.If the mobile hard disk box has a high power demand,sometimes it is necessary
to connect two USB interfaces.Use,otherwise,need an external power supply.But now most new hard
disk enclosures(using 2.5-inch or smaller hard disks)can easily use a single USB port for power
The physical structure of a hard disk is generally composed of magnetic heads and
disks,motors,main control chips,and cables;when the main motor drives the disks to rotate,the
auxiliary motor drives a group(heads)to the corresponding disks and determines Read the front or
back side of the disk.The magnetic head is suspended on the disk surface to draw a circular
track(track or cylinder)concentric with the disk.At this time,the magnetic induction coil of the
magnetic head senses the magnetic and magnetic properties on the disk surface.Use the read time
or data interval specified by the hard disk manufacturer to locate the sector to obtain the data
content of the sector;
When the disk rotates,if the head is held in one position,each head will draw a circular track on
the surface of the disk.These circular tracks are called tracks.
In a disc group composed of multiple discs,a cylindrical surface(Cylinder)composed of multiple
tracks with different disc faces but in the same radius circle.
Each track on the disk is equally divided into a number of arcs,and these arcs are the sectors of
the hard disk.The first sector of the hard disk is called the boot sector.
The speed of the hard disk platters is extremely fast,and the distance from the platters is
extremely small;therefore,the inside of the hard disk is dust-free,and the hard disk has a
filter to filter the air entering the hard disk.In order to prevent the head from hitting the
disc,manufacturers have devised various protection methods;at present,hard disks have good
protection against earthquakes(some hard disks in the 1990s,if they encounter a slightly larger
earthquake in use,they are likely to be damaged).The ability to fall has also been greatly
improved.When the power is turned off and large vibrations are encountered,the heads will
immediately move to the safe area(recent hard disks have also begun to prevent sudden power
failures);and many notebook computer manufacturers have also developed various notebook computer
structures.Strengthen the drop resistance of the hard disk.However,when the hard disk is powered
on,its resistance to drop(rotational inversion)will be reduced,and it can only be moved
gently.Many people have developed that they will not move the hard disk(and laptop)within 30
seconds to one minute after turning off the hard disk.habit.
After 2010,helium encapsulation technology was mass-produced.In the past,the filling medium of
hard disks was air,but it was easily affected by air.Therefore,the distance between the platters
must be sufficient.The density of helium is much smaller than that of air.The characteristic is
stability.Using it as a medium,the resistance and vibration are relatively small,so the distance
between the platters can be reduced,so more platters can be installed in the same space.The
advantage of using helium packaging is that the capacity is changed.In addition,the temperature
and power consumption can be further reduced,so the durability and stability can be further
When the operating system reads and writes to the hard disk,it needs to use the file system to
combine the sectors of the hard disk into clusters,and create a file and tree directory system
to make it easy for the operating system to access and find it because of the operation It would
be very troublesome for the system to directly address a large number of sectors.
MBR and GPT
Master Boot Record Record(abbreviation:MBR),also known as the master boot sector,is the first
sector that must be read when the computer is booted to access the hard disk.The master boot
sector records information about the hard disk itself and the size and size of each partition of
the hard disk.Location information is an important entry point for data information.If it is
damaged,the basic data structure information on the hard disk will be lost.It is necessary to
use a tedious way to tentatively reconstruct the data structure information before re-accessing
the original data.For those disks with 512-bit sectors,MBR partitioning The table does not
support partitions with a capacity greater than 2.2TB(2.2×1012 bytes).
Globally uniquely identify the partition table(GUID Partition Table(abbreviation:GPT)is a
standard for the structure and layout of the partition table of a physical hard disk.It is part
of the Extensible Firmware Interface(EFI)standard(used by Intel to replace the BIOS of personal
computers).GPT allocates 64 bits to the logical block address,thus making it possible for the
maximum partition size to be 264-1 sectors.For a disk with a sector size of 512 bytes,that means
there can be 9.4ZB(9.4x 1021 bytes)or 8 ZiB-512 bytes(9,444,732,965,739,290,426,880 bytes or
18,446,744,073,709,551,615(264-1)sectors x 512(29)bytes per sector)
The size and purpose of hard drives can be divided into:
- 0.85 inches,mostly used in portable devices such as mobile phones,and has been discontinued.
- 1 inch(micro hard drive,MicroDrive),mostly used in digital cameras(CF type II
interface),currently has been discontinued.
- 1.8 inches,mostly used in notebook computers and external hard disk enclosures,it is
- 2.5 inches,mostly used in notebook computers and external hard drive enclosures.External
hard disk enclosures with 2.5-inch hard disks generally do not require an external power
- 3.5 inches,mostly used in desktop computers.However,external hard disk enclosures with 3.5"
hard disks generally require an external power supply, because the power consumption exceeds
the upper limit of USB power supply, and the 3.5-inch hard disk requires 12v voltage.
- 5.25 inches, mostly used by early desktop computers, has been discontinued.
- 10.5 inches.
- 14 inches, such as NEC DKU800
In addition to the interface and size, the hard disk has the following parameters:
||The most important parameters of hard disks. At present, the capacities of hard
disks are 36GB, 40GB, 45GB, 60GB, 75GB, 80GB, 120GB, 150GB, 160GB, 200GB, 250GB,
300GB, 320GB, 400GB, 500GB, 640GB, 750GB, 1TB, 1.5TB, 2TB, 2.5TB, 3TB, 4TB, 5TB,
6TB, 8TB, 10TB, 12TB, 14TB, 16TB, 18TB and many other specifications, but the
|| The number of revolutions per minute of the hard disk, in rpm (Revolutions Per
Minute, the number of revolutions per minute), there are 4200rpm, 5400rpm, 5900rpm,
7200rpm, 10000rpm, 15000rpm, 18000rpm and other specifications. Generally speaking,
the higher the rotation speed, the better the data transmission rate, but at the
same time the higher the noise, power consumption and heat generation.
||There are mainly 2MB, 8MB, 16MB, 32MB, 64MB, 128MB, 256MB and other specifications.
|Average seek time The unit of|| is ms (milliseconds), with 5.2ms,
8.5ms, 8.9ms, 12ms, etc.
|Internal transmission speed
|| includes the speed at which the head reads data from the disk into the cache, and
the speed at which the head writes data from the cache to the disk. It can be used
to evaluate the read and write speed and overall performance of the hard disk.
In addition to voltage, current, etc., solid state drives also have parameters such as master
control and particle type (SLC, MLC, TLC, QLC). Generally, 3.5-inch hard disks in mechanical
hard disks require 5V and 12V voltage, and 2.5-inch hard disks only need 5V voltage. However,
because of the mechanical structure, the power consumption is usually higher than that of
solid-state hard disks; the voltage of solid-state hard disks is generally 5V or 3.3V, and at
the same time The power consumption of solid-state hard drives is usually low (power consumption
is about 2.5W, current is about 500mA), and it is more energy-efficient than mechanical hard
History of Development
||IBM'sIBM 305 RAMACIBM 305 RAMAC) is the prototype of a modern hard disk,
which is equivalent to the volume of two refrigerators, but its storage capacity is
||This year IBM 3340 came out, it has the nickname "Winchester", derived from its two
30MB storage units, which happened to be the caliber and filling of the famous
"Winchester Rifle" at the time the amount. So far, the basic structure of the hard
disk has been established.
||The company founded by two former IBM employees has developed a 5.25-inch 5MB hard
drive ST506, which is the first desktop-oriented product, and the company is
||IBM launched MR (Magneto Resistive magnetoresistance) technology greatly improves
the sensitivity of the magnetic head, and increases the storage density of the disk
by dozens of times compared with the previous 20Mbpsi (bit/square inch). This
technology lays the foundation for a huge increase in hard disk capacity. In 1991,
IBM applied this technology to launch the first 3.5-inch 1GB hard drive.
|From 1970 to 1991
||The storage density of hard disk platters has been increasing at a rate of 25% to
30% per year; it has increased to 60% to 80% since 1991; so far, the speed has
increased to 100% or even 200%. The amazing speed increase since 1997 has benefited
from IBM's GMR (Giant Magneto Resistive (Giant Magneto Resistance) technology, which
further improves the sensitivity of the magnetic head, thereby increasing the
||Conner Peripherals launched the CP30344 hard drive with a capacity of 340MB.
||In order to cooperate with Intel's LX chipset, Quantum and Intel jointly release
UDMA 33 interface-EIDE standard increased the original interface data transmission
rate from 16.6MB/s to 33MB/s. In the same year, Seagate developed fluid dynamic
bearings (FDB, Fluid Dynamic Bearing) electric motor. The so-called FDB refers to
the introduction of the technology on the gyroscope into the production of hard
disks, replacing metal bearings with an oil film that is one-tenth of the diameter
of a hair to reduce the noise and heat generation of the hard disk.
||Seagate acquired Conner Peripherals.
||UDMA 66 parameters are available.
||Maxtor acquires Quantum.
||Hitachi announced the completion of the US$2.05 billion acquisition of the IBM hard
disk business unit and the establishment of Hitachi Global Storage Technologies
a> (Hitachi Global Storage Technologies, Hitachi GST).
||Hitachi Central Storage and Seagate have both announced that they will begin to
adopt disk vertical writing technology (perpendicular recording), the principle is
to change the direction of the magnetic field parallel to the disc to vertical (90
degrees) to make fuller use of storage space.
|December 21, 2005
||Seagate announced the acquisition of Maxtor.
||Hitachi Global Storage Technology announced that it will sell the world's first
1Terabyte hard drive, more than a year later than the original schedule. The price
of the hard drive is $399, and an average of 27.5MB of hard drive space can be
purchased for every cent.
||Western Digital acquired Hitachi Global Storage Technology for $4.3 billion.
||Seagate announced that it has strengthened its strategic partnership with Samsung,
and traditional hard drives are gradually being replaced by solid state drives.
||Seagate announced the acquisition of Samsung's hard drive business.
Existing major hard drive manufacturers
- Western Digital (Western Digital) and its subsidiary Qantas Global Storage (HGST)
- Hitachi Global Storage Technology: In 2011, it was acquired byWestern Digital
and renamed Yuke Global Storage (HGST).
- IBM: In 2003, the hard disk division was acquired by Hitachi.
- Conner: Acquired by Seagate in 1996.
- Maxtor: Acquired by Seagate in 2006.
- Quantum: In 2000, the hard drive division was acquired by Maxtor.
- Samsung: In 2013, the hard disk business was acquired by Seagate.
- Fujitsu: On February 18, 2009, the hard disk division was acquired by Toshiba.