This article offers detailed introduction to hard disk, including its types, main types of interface, physical structure, logical structure, and so on.

Hard disk is one of the computer’s main storage medias. It is composed by one or more of aluminum or glass platters. The disk is covered with ferromagnetic materials. The vast majority of the hard disks are permanently fixed in the hard disk drivers.

Brief Introduction

Types of Hard Disk

Hard disk can be divided into three types:

1. Solid-state drives (SSD, the new hard disk), which adopt flash particles to store.

2. Mechanical hard disk (HDD, traditional hard disk) usually uses magnetic Disk to keep data.

3. Mixed hard disk (HHD or Hybrid Hard Disk, a new hard drive which is based on the traditional mechanical hard disk). It is the hard disk which integrates the magnetic disk and flash memory together.

Tip: Considering that you may want to migrate OS to a new SSD or HDD, we recommend MiniTool Partition Wizard.


1. Head reset and energy saving technology:do head restoration at leisure to reach the goal of energy conservation.

2. Multi-head technology (often applied in server and database center): adding multiple heads on the same disk to accelerate disk read/write speed. Or using multiple magnetic heads on multiple disks to improve read and write speed.


As a data memorizer in computer system, disk’s main parameter is capacity. Hard disk capacity units: megabytes (MB/MiB), gigabyte (GB/GiB), terabyte (TB/TiB) 

Note: Conversion formula: 1 TB = 1024 GB, 1 GB = 1024 MB, 1 MB = 1024 KB 

Manufacturers often use GB (1 g = 1000 MB) as a hard disk unit. But in Windows operating system, it is still using the word”GB” to represent the”GiB”. So, when in the BIOS or in the process of formatting, we can see the disk capacity is smaller than the manufacturer’s nominal value.

Hard disk capacity indicator also includes single disk capacity. The larger the single disk capacity is, the lower the unit cost is. As a result, the average access time will be shorter.

Usually, the greater the hard drive capacity is, the cheaper the unit byte is (except for the hard disk which owns larger capacity than the mainstream’s).

Rotational Speed/Spindle Speed(R/M)

The rotational speed is an important parameter to mark the hard disk class. It is the key factor to decide the internal transfer rate. What’s more, it directly affects the speed of the hard disk. If the speed is high, the access time will be shorter and the hard disk overall performance can also be better.

Rotational speed of household hard disk is 5400 R/M or 7200 R/M. Laptop users often use the disk with rotational speed of 4200 R/M or 5400 R/M. Some companies have released the notebook hard disk with 10000 R/M (relatively rare to see in current market).

Server users ask for the highest performance of hard disk, and its SCSI’s rotational speed always adopts10000 R/M or even 15000 R/M. Rotational speed in server requires higher performance than in household products.

High spindle speed can shorten the average seek time and the actual reading and writing time. With the constant improvement of the hard disk rotational speed, some problems (like motor spindle wear and working noise) also appear.

Average Access Time

This concept is used to measure the time head takes to travel the disk track until needed data are found. It embodies the hard disk read and write speed. The average access time includes hard disk seek time and waiting time.

The Average Seek Time starts when the head moves and ends when the specified track is found. The shorter the better.

Note: The disk average seek time usually ranges from 8 to 12 ms, and the average seek time of SCSI hard disk should be less than or equal to 8 ms.

Waiting time or latency is the time used for bringing the required sector under the read-write mechanism. The average latency is one-half of the rotational period.

Data Transfer Rate (MB/s)

Data Transfer Rate means the hard disks’ read and write speed. It can be divided into internal and external data transfer rate.

Internal Transfer Rate, also known as Sustained Transfer Rate, can reflect the performance when hard disk buffer is not available. It mainly depends on the hard disk rotational speed.

External Transfer Rate, or Burst Data Transfer Rate, is the transfer rate produced by system bus and hard disk buffer. It is associated with hard disk interface type and the cache’s size.

For Fast ATA interface, the biggest external hard drive transmission rate is 16.6 MB/s. And as for Ultra ATA interface, the speed can reach to 33.3 MB/s. 

In 2012, two young men developed a SSD with the transmission speed of 1.5 GB per second.

Cache Memory

Cache memory lies in the hard disk controller. It is the buffer between hard disk internal storage and external interface. Size and speed of cache can directly affect the hard disk transmission rate. Cache can greatly improve the hard drive overall performance. When hard disk gives access to data, constantly exchanging data between the disk and memory is a must. If there is a large cache, you can store the temporary data into the cache to reduce the system load and improve the data transmission speed.

Types of Interface

1. IDE (Integrated Drive Electronics)

It is commonly known as PATA parallel port.

Hard Disk 3

2. ATA (Advanced Technology Attachment)\

It uses the traditional 40-pin parallel port cable to connect the motherboard and hard disk. The maximum speed of external interface is up to 133 MB/s. Because of the poor anti-jamming and bad computer cooling, parallel line will be gradually replaced by SATA.

Hard Disk 4

3. SATA (Serial ATA)

It adopts serial connection mode. The Serial ATA bus uses embedded clock signal, and it has stronger ability of error correction. Compared with the previous ones, it can check the transferring instruction and correct errors automatically.


Unlike SATA, SATA II’s external transfer rate has been improved from 150 MB/s to 300 MB/s. What’s more, it also owns other features like NCQ (Native Command Queuing), Port Multiplier, Staggered Spin-up and so on. But not all of the SATA hard disks can support NCQ technology. Not only the hard drive, but also the SATA controller of mainboard chipset should support NCQ.

SATA III (SATARevision3.0)

The transmission speed has been doubled to 6 Gbps. It is compatible with “SATARevision2.6” (or SATA3Gbps). The interface and data line don’t get changed.

4. SAS (Serial Attached SCSI)

It adopts the serial technology to gain higher transmission speed. And it improves the internal space by shortening the link line. This interface is designed to optimize the efficiency of storage system, availability and expandability. And it also provides compatibility with SATA hard disk.

5.SCSI (Small Computer System Interface)

It is completely different from IDE ATA). The IDE Interface is ordinary PC standard Interface. And SCSI is not specially designed for hard disk. It features a high speed data transmission technology widely used in small machines. SCSI interface has many advantages like wide application range, multitasking, large bandwidth, low CPU usage and hot plug. Due to the high price, it is hard to get popularized. Therefore, SCSI is mainly applied in medium or high-end servers and high grade workstations.


Seagate– productions are mainly used for enterprises, desktop computers, mobile devices and Consumer Electronics (CE).

(Note: Seagate has launched the world’s thinnest 2TB mobile hard drive in 2016. )

Western Digital – providing storage products for all five continents.

(Note: It is said that Western Digital® Corporation has completed the acquisition of SanDisk Corporation on May 12, 2016.)

The post – Free WD External Hard Drive Data Recovery Is Under Control is ready to tell you the details on WD HDD recovery whenever you want to know.

HITACH – mainly produces desktop computer hard disks and notebook hard disks. Then it was acquired by Western Digital.

TOSHIBA – main productions are mobile storage devices.

(Note: A Toshiba external hard drive may fail to be recognized by computer, you should deal with the problem calmly and patiently.)

Samsung – its hard disks are used for desktop computers, mobile devices and electronics products. In 2011, Seagate purchased Samsung’s hard drive business.

(Note: Data may be lost from a Samsung device suddenly; here, we take Samsung Galaxy S6 data recovery as an example to show you how to recover data from Samsung device.)

Different Sizes

  • 5 inch desktop hard drive– it is widely used in all kinds of desktop computers.
  • 5 inch notebook hard disk– used in notebook, all-in-one computer, mobile hard disk player and portable hard disk.
  • 8 inch micro hard disk– it is applied in ultrathin laptop, mobile hard disk and apple player.
  • 1.3 inch micro hard disk– this is only for Samsung mobile hard disk.
  • 0 inch micro hard disk (developed by IBM) – Satisfying the CF II standards, MicroDrive micro hard disks (or MD) can be found in digital SLR camera.
  • 85 inch micro hard disk– it is used only by Hitachi.

Fiber Channel

It is developed for improving the speed and flexibility of the hard disk storage systems. It is developed to greatly improve the communication speed of multi-hard disk system. Its main features are hot plug, high-speed bandwidth, remote connection, and support on large quantity equipments. 

Fiber channel is designed for server hard disk system. It can meet the needs for high data transmission in high-end workstations, servers, mass storage sub-network, and peripherals through hubs, switches and point-to-point connection between two-way or serial data communication system.

Tip: Hard drive crashes easily, no matter what kind of interface it has (IDE, ATA, SATA, SCSI, etc.). Therefore, we think it’s necessary to show you how to recover important data after hard drive crash.

Physical Structure and Logical Structure of Hard Disk

Physical Structure

Magnetic Head:

Heads are not only the most expensive part of hard disk but also the most crucial link in hard drive technology. Traditional head is electromagnetic induction head which is a combination of reading and writing. But the operations on reading and writing are totally different from each other, which lead to the limitation in the hard disk design.

Magneto resistive heads use a separate head structure: write head still adopts the traditional induction head and read head uses the new type MR head. In addition, through the changes of resistance, the MR heads can induct the changes in signal amplitude. It is quite sensitive to signal changes, and also can increase the data reading accuracy.

Reading signal amplitude has nothing to do with the track width, so the track can be made narrow so as to improve the density (to 200MB per cubic inches) of the disk. MR heads have been widely used. The GMR (Giant Magneto resistive) heads which use the multi-layer structure and materials with better magnetic resistance effect) also began to spread.


On a hard disk drive, the circular part which can be used without moving the drive’s access arm is called track. There are concentric circles in the disk surface and information is stored in them. Each circle equals to a track. A few hundred to a few thousand tracks exist on a disk range (a modern hard disk even has tens of thousands of tracks on each platter<).


A disk track can be divided into many arcs, and these arcs are called disk sector. Data can be located by knowing the number of the sector and the concentric track that passes through that sector.


Hard disk usually consists of a set of disk platters, and each of them is divided into equal number of tracks.

When the head for one surface is on a track, the heads for the other surfaces are also on the corresponding tracks. All the corresponding tracks taken together are called a cylinder. A cylinder, composed by tracks, is a division of data in disk. The amount of disk cylinders is the same as the amount of tracks. 

Logical Structure

3D Disk Geometry:

Many years ago, people used structure which similar to that of the floppy disk drive to produce hard disks. It means that each track of the hard disk has the same number of sectors.

Then there comes the 3D Disk Geometry, namely the Heads (255 to the largest number-with 8 binary storage), Cylinders (1023 to the largest number-with 10 binary storage), Sectors (63 to the largest number-with six binary storage) and the corresponding way of addressing.

BIOS interrupt call 13hex:

It is used to transfer interrupt information in the process of inputting and outputting. It can complete many functions like disk reset, reading and writing, calibration, positioning, diagnosis, formatting and so on. It adopts the CHS addressing mode, so it can only access 8 GB hard drive at most (1mb = 1048576 bytes).

In order to break the limitation of 8 GB, West Phoenix and Digital Technologies jointly launched the EDD standard (BIOS Enhanced Disk Drive Services) to support 64-bit LBA. It also can support the removable media (such as active hard Disk).

Modern Structure:

In the old fashionable hard disk, each track shares with the number of sectors. The recording density of the outer track is much lower than inner track which will waste a lot of disk space (like the floppy disks)

In order to solve this problem to improve the hard drive capacity, people changed the density structure. That is to say, the number of outer track sectors is larger than that of inner track. After that, the hard drive no longer owns the 3D Disk Geometry. And the addressing mode is also changed to linear addressing (or using sector for addressing).

In order to be compatible with the old software which uses the 3D Disk Geometry, an address translator (responsible for translating the old 3D Disk Geometry into new linear parameters) is installed into the hard disk controller.

Since a RAID card may employ different types of interface, so here we give a brief introduction to the advantages of RAID. 

1. Fast transmission rate

It can make many disk drives transmit data at the same time in some RAID mode. And these disk drives are logically grouped in a disk drive. Therefore, RAID can achieve a rate that is much faster than single disk drives. The speed of the CPU is growing rapidly but disk data transmission cannot be significantly improved, so you need to have a plan to solve the contradiction between them.

2. Higher security.

Compared with ordinary disk drives, RAID mode provides a variety of data repair functions. When a disk drive suffered severe fault, you can use other disk drive in RAID to restore the data.

Maintenance Information About Hard Disk

Signs of Hard Disk Failure

S.M.A.R.T troubleshooting tips.

1. This is a built-in automatic detect program in hard disk. It means that there are some physical faults in your hard disk.

2. Frequent but irregular crashes, especially while booting up Windows.

3. Error occurs when we are running a program, or the OS even gets crashed when we are scanning disk.

4. A number of errors or bad sectors are scanned out. And the checking procedure of Windows will report in detail.

5. Hard disk cannot be recognized in BIOS. Or it can be found in BIOS but Windows cannot find it. This is the most serious breakdown.

Note: Please get to know the 10 signs that may lead to hard disk failure.

Maintenance Tips of Hard Disk

1. Be careful about the surrounding environment

Hard disk uses breathing hole which has a super-fine filter to communicate with the outside world. And it can work in the indoor environment that doesn’t have a purification device. Using it in hot, cold, dusty or humid circumstances will make the disk suffer from damage.

2. Shut down the computer in right order

Please pay attention to hard drive light in the panel. Only when the light stops flicking, you can turn down the computer. Preventing the machine from being shut down improperly may make the hard disk get rid of destroy.

3. Don’t move the hard disk when it is running.

When the disk runs at high speed, gentle shake may generate friction between head and disk platter. In the process of mounting or dismounting, behaviors like violent shaking or collision should be avoided.

4. Reduce frequent operations on a program or on an operation system

Reading and writing on the same part of a hard disk will produce bad tracks. You can install two operation systems to avoid reading and writing on a sector for a long time. 

5. Properly use the hard disk

Under the environment of high temperature in summer, you’d better make your hard disk work for less than 10 hours. What’s more, it shouldn’t work continuously for 8 hours.

6. Defragment that drive at fixed period

Due to frequent operations, free sectors in disks will be scattered to discontinuous parts of the disk. Therefore, the files cannot be kept to continuous sectors. When reading and writing, the head will move back and forth, which will slow down the disk access speed and influence disk service time. Making defragmentation at regular intervals is really a must.

Note: Since the writing way is different from Windows, Linux or Mac OS don’t need to clean up the fragments.

Please click here to know the benefits of defragmentation and how to defrag in Windows

7. Provide stable power supply

Users should use the power with stable performance. Once the power supply is not stable or insufficient, it will be easy to cause data loss or damage to hard disk.

8. Don’t force the computer to shut down

This will produce strong friction between the hard disk and the head pointer. After a long time, the hard drive track will get damaged.

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