Hard disk


A hard drive shortened in HD in English is a physical storage medium that allows you to keep all your data (photos, music, movies, files, folders, …).


It is called “mass memory” because it can hold a very large amount of data. It is also called “ROM” because, in case of power off your computer, the information stored there is not erased and therefore remain.


It is used on the computer but also in other devices such as a camera, video game consoles.


Since its invention, the hard drive has undergone many transformations as well from the point of view storage capacity as the design.


In this article, we will talk about the features, the mode of operation and many other things related to the hard drive.


Internal structure and operation of a hard disk.


A hard disk consists not only of a single disk but of several disks called trays acting as a storage medium and superimposed on each other at a very short distance can be glass, ceramic or metal.


These discs, called platters, revolve around an axis and can go up to thousands of revolutions per minute.


To read the data stored on your hard disk more on the storage medium, the latter uses what is called reading head. The latter is placed on the superimposed platters in rotation and reads or writes the data on the disk. The movement of the read head during reading or writing is handled by the disk controller. The data are written in a binary form in a sequence of 0 and 1 because the computer can only understand this language.


What are the characteristics of a hard disk?


There are five main features of hard disk:

  • Storage capacity

It means neither more nor less than the amount of digital data (photo films, video files, folders) that can hold your hard drive. Depending on the capacity, you can have hard drives up to hundreds of terabytes.

  • Speed of access time

This is the average time between moving the read head from one data block to another.

  • Speed of rotation of trays

This is the speed at which the platters rotate. We express it in the number of revolutions per minute.

  • Transfer rate.

This is the amount of data that can be read or written per unit of time.

  • Cache or cache memory.

Located inside the hard drive itself, it is a memory that allows the driver to keep copies of data from other sources such as RAM to minimize access time.


Types of hard drives.


Depending on the format, there are internal hard drives that are connected to the motherboard and external hard drives that can be added to the computer through an external USB port.


Depending on the size, we can categorize them in three:


  • The 5 inches (ca. 13 cm).
  • The 3.5 inches (ca. 9 cm).
  • The 2.5 inches (6.35 cm).


We categorize hard drives into three types, traditional HDD, electronic hard drives or SSD, and finally hybrid or SSHD disks.


Traditional HDD.


Characterized by their mechanical components, there are several types namely:


IDE Hard Disk.


Looking closely at the motherboard of your computer, the big, blurred circuit board on which all the internal elements are connected, you can see two big notches, one close to the other. These are the IDE-ports to which connectors are connected in the form of a web called IDE web. Each of these layers is equipped with two IDE connectors the first or main called master and the secondary slave.


The hard disk connected to the main connector will be the master, i.e. the fastest hard disk and the hard disk connected to the second connector will be the slave, i.e. the hard disk. Slower. The operating system is installed on the master hard disk for reasons of speed.


SCSI hard disk.


The motherboards equipped with the SCSI controller are more efficient than those equipped with the IDE controller. The SCSI layers are wider than the IDE layers and can accommodate up to seven hard drives each with a number called SCSI ID to differentiate them from each other.

SATA hard drive.


The advantage of this hard disk is the absence of a cumbersome sheet, as with IDE hard disk.


There are two connectors, one for powering the hard drive and the SATA connector for transferring data from the hard drive to the main memory that is the RAM. Another significant advantage found here is the speed of data transfer, which is important.


SSD hard drive.


Unlike all the other types mentioned above, an SSD is not mechanical. A hard disk is said to be mechanical when it comprises trays used as a storage medium and a read head that moves with each reading or writing on the disk.


It uses electronic storage media much like for RAM, except that unlike RAM, the SSD stores data sustainably.


The latter has a huge speed because it has flash memory. Given the absence of a mechanical component, this disc produces virtually no noise and almost no heat or very little less than a conventional disc.


SSD hard drives are faster (both reading and writing) have some disadvantages; However, the most important is probably the very high volume/price ratio. Often 10 or 20 times higher than a conventional disk for the same capacity.


SSHD Hard Disk (Hybrid Disk)


They feature both mechanical storage components and conventional hard drives and electronic storage components and SSD.


Operation of a conventional hard disk.


In hard disks, the read heads are said to be inductive; They can generate a magnetic field. When writing when the read head writes the data to the hard disk, it creates a positive or negative field as the case and this mechanism creates a current which will then be converted by a converted digital-analog is in 0 or 1 as appropriate and written on the disc.


The writing or writing of the data is done on the disc from the edge to the center of the disc. The inscribed data form a concentric circle having the same center called tracks. The smallest area that can occupy data on the hard disk is called “allocation unit” or “cluster” in English.


Likewise, conventional hard drives having mechanical components, although less rapid than SSD, have a huge advantage in terms of resistivity and durability.


To couple or integrate both the advantages of the SSD and conventional hard disks having mechanical components, SSHD or hybrid hard drives were invented.


Operation of an SSHD hard disk.


How does a hard drive with both electronic and mechanical components work? How can the disk know if it should write the data on the mechanical part that is to say the trays or the electronic part that is the flash memory? You will need to know first that it is not the hard disk that decides to write the data on the storage medium, whether mechanical or electronic. This choice is made by an element called the “disk controller”.


With SSHD, two scenarios can occur:


Scenario 1


When you write (store) something like a movie you just had on your hard drive, the hard disk controller stores that data on the mechanical part of your SSHD drive. Keep in mind that when the film is stored in the mechanical part, the access time can be large.


Scenario 2


When you have often accessed data for example when you often follow the same music on your computer, the disk controller will take this music and write it or store it in the electronic support to reduce the access time and increase the speed of reading. From now on when you read your music, you notice that it starts faster.