Dry want to drink water, an article takes you to read the hard disk working principle!
2020-12-08 14:01:30 【osc_ t6qz550e】
I want to drink water , An article takes you to understand how hard drives work ！
One 、 The basic structure and working principle of hard disk
1956 year 9 month ,IBM An engineering team showed the world the first disk storage system Ramac,1968 year ,Winch? Juan ester technology （ Hotplate Technology ） Proposed , From then on, human beings began to move from sequential storage to random storage , after 50 The vicissitudes of the year , It has always been the prototype of modern hard drives . Modern hard disks are mainly made of 「 Disc body 」、「 The integrated circuit 」、「 Interface 」 And so on , Its appearance is shown in the figure below ：
If you remove the IC board from the picture , We can see the disk body , The disc body is a sealed cavity , There are magnetic disks in it 、 Read write head 、 Motor and other major components , Take the hard disk apart , Its internal structure is at a glance .
「 Disc 」 It's a disk storage medium used to hold a large amount of data , For high density 、 Highly stable aluminum alloy or glass material , The surface is smooth, smooth and flawless , A thin layer of high density magnetic powder was uniformly sprayed , It is then coated with graphite for protection and lubrication . At present, desktop hard disk mainly uses 「3.5 Inch plate 」. The disc is set on the main shaft of the motor , Driven by an electric motor, it rotates at high speed , The maximum speed can exceed 「15000 turn / minute 」, When obtaining evidence, we often encounter 7200 RPM or 5400 RPM.
At present, there are 「 Stepper motor 」、「 Torque motor 」 and 「 Voice coil motor 」 Three , Now we mainly use voice coil motor . The magnetic head is a thin film read-write head , Fixed to the head arm , When seeking, it moves with the arm of the magnetic head . The above is the simplest mechanism , Today's disks are basically double-sided magnetic plating , So magnetic heads are often divided into up read and write heads and down read-write heads , The disc is clamped on it 、 The bottom reading head rotates in the middle , If there is more than one disc （ Usually it is 3 Zhang , The middle is separated by a gasket ）, There are more heads of this kind , But they're all fixed to the same set of arms , When moving, the whole set of magnetic head arms moves as a whole , In this way, the disk capacity and read-write speed can be doubled .
We can use Winchester Principle to describe the working process of hard disk ：“ seal up 、 Fixed and high-speed rotating plated disk , The head moves radially along the disk , The head is suspended above the high-speed rotating disk without direct contact with the disk ”. This is the prototype of most modern hard drives .
The hard disk is 「 Delicate and fragile 」 Electronic equipment of , It's because of the above structure and working principle , So for hard drives that look solid , We also need to be careful about it when we take evidence . for example ： Before connecting the power supply , Keep it in an antistatic bag , When collecting evidence on the forensics machine, it should be fixed with a fixed device , And in the process of operation, it should be placed on the table which is not easy to shake , The working environment should be dry 、 Less dust 、 No static electricity , And there should be no strong magnetic field nearby , If we need to open the disk , You have to go in 「 Wind shower room 」（clean room） 了 .
Two 、 The storage principle and structure of hard disk
We all know that magnets have two polarities , One is 「 The South Pole 」（S extremely ）, One is 「 arctic 」（N extremely ）, Hard disks use the polarity of magnetic particles to record data . The magnetic particles on the surface of the disk are magnetic particles . The disc is divided into concentric circles （ It's called track ）, On the track of each concentric circle, there are countless small magnets arranged randomly , When these little magnets are affected by the magnetic field from the head , The direction of the alignment changes , Use the magnetic force of the magnetic head to unify the direction of small magnets in a certain area , So that the magnetic field in the region is of the same polarity , If you put S/N Two kinds of polarity and binary 0 and 1 Corresponding , You can represent binary data , These magnetic particles are permanent magnets , Even if the head leaves , It can still maintain its polarity for a long time , In this way, the purpose of storing information can be achieved . When the head reads data , It can sense the different polarity of magnetic particles , So it can be converted into different electrical pulse signals , These signals are translated by the decoder , It becomes data that computers can use .
Before explaining the storage structure of the hard disk , It is necessary to introduce the following pilot concepts ：
Disk surface ：
Every disc has 、 The bottom two sides （Side）, Both sides will be used to store data , Become an effective disk （ There are also individual hard disks with only one side ）. Each active disk has a disk number , From top to bottom “0” Start numbering in sequence , Because each effective disk corresponds to a read-write head , So the head number is equivalent to the disk number . Usually a hard disk has 3 The same disc , So magnetic number one （ Disk number ） The number is 0 to 5.
Magnetic track ：
The disc is divided into many concentric circles in low-level format , These concentric circles are called tracks （Track）. The track is outward and the center is from 0 Start sequence number , There are usually thousands of tracks on a disk . Pay attention here , Tracks are invisible , It's just some polarized magnetized regions on the disk , But a disk with data can be identified under a magnetic microscope . When the disc rotates , Track angular velocity is the same , But because of the different radii , Its linear velocity is different . What we usually say is 0 A track is the outermost ring of a disk's effective area .
When there are more than one disc , In three dimensions , All tracks of the same radius on the disk form a cylinder , It's called a cylinder （Cylinder）, So the number of cylinders in a hard disk is equal to the number of tracks on each disk . for example , Three hard disks of ,0 The cylinder refers to the three disks 0 A cylinder of magnetic tracks .
Physical sector ：
Low level formatting divides tracks at the same time , Each track is divided into segments 「 arc 」, Each arc is called a 「 Physical sector 」（Sector）, from 1 Numbered starting （ The previous concepts are all derived from 0 Numbered starting ）, In the current industry standard , A track is often divided into 63 Physical sectors , Of course, a track can also be divided into more or fewer sectors , But generally it should be odd , It's mainly out of consideration of the interval factor （ It's also called cross factor ） Why , Limited to space , I won't go into details here . The operating system doesn't record data continuously on tracks , Instead, the data in each physical sector is read out or written as a basic unit , So the sector is the basic unit of read and write data on the hard disk （ The unit of data storage is “「 cluster 」”, The contents of a logical part of a file system , It's not discussed here ）. Each sector contains two main parts ： Data address segments and data segments , Under normal circumstances , Each sector includes 512Byte The data and 4Byte Other information .
After clarifying the above concepts , How do we represent our own hard disk space . The hard disk stores the first few bytes of each physical sector CHS Number , there C、H、S They are cylindrical 、 head 、 Sector the first letter of three English words . in other words , In the three-dimensional space of a hard disk , According to the previous numbering rules , We just need to know the cylinder where the physical sector is 、 Head and sector numbers , We can determine its unique location , You can also use their values to calculate the total capacity of the entire hard disk . The calculation formula is as follows ： Disk capacity ＝ Cylinders × Number of tracks per cylinder × Number of physical sectors per track × Number of sector bytes per physical sector, e.g ： A hard disk has 3 Aluminum alloy disks , Data is stored on both sides of the disk , Each side is low-level formatted as 2048 Tracks , And each track is divided into 63 Physical sectors , Each physical sector can store 512 Bytes , The total capacity of this hard disk is ：2048×6×63×512=396361728 Bytes , about 378MB（ In this case ① The relevant parameters are not actual hard disk parameters , Just to explain the principle ;② Here we assume that a cluster contains only one sector . Hereby explain .）
at present , The capacity of hard disk can reach hundreds of GB, And the level of data storage has reached TB level . For units of measurement , It is necessary to explain here ,1Bit I.e. storage 0 or 1 A binary bit of ,1Byte Of a byte , The common conversion relations are as follows ：
1Byte=8bit 1KB＝210B＝1024 Byte 1MB＝210KB＝220B＝1048576 Byte 1GB＝210MB＝220KB＝230B =1073741824 Byte 1TB＝210GB＝220MB＝230KB＝240B =1099511627776 Byte 1PB＝210TB＝220GB＝230MB＝240KB =250B =1125899906842624 Byte 1EB＝210PB＝220TB＝230GB＝240MB =250KB =260B =152921504606846976 Byte
About hard disk capacity , We often have this problem ： Why the same hard disk , Sometimes it shows 60GB, Sometimes it's just 56GB？ This is caused by the disunity of measurement units , When the operating system makes statistics 1KB=1024 Byte, But hard disk manufacturers use 1KB=1000Byte To calculate , This leads to the above problems , It's not the loss of space in the hard disk , Or the criminals have hidden the space .
3、 ... and 、 Summary
The above content introduces the basic structure of hard disk from the point of view of physical characteristics 、 Working process and storage principle , I hope to further understand the principles and procedures of electronic forensics , And skilled operation of forensics and data recovery software can help .
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