First of all, let's take a look at the working principle of mechanical hard disk.
1 Working principle of mechanical hard disk
The internal structure of a mechanical hard disk is mainly composed of a motor, a disk, a magnetic head arm, and a magnetic head.
When the mechanical hard disk is working, the magnetic head will be suspended a few nanometers above the disk surface. There are many small grids on the surface of the disk, and there are many small magnetic particles in the small grids.
The magnetic particles on these disks have a certain polarity. When the polarity of the magnetic particles is facing down, it is recorded as 0, and when the polarity of the magnetic particles is facing up, it is recorded as 1. In this way, the magnetic head can read the data by identifying the polarity of the magnetic particles of the disk. The data is fetched.
The magnetic head can also use its changing magnetic field to change the polarity of the magnetic particles of the disk, so that the data on the disk can be written and rewritten.
In order to accurately locate the position of the data on the disk surface, the disk itself is divided into numerous sectors and tracks.
Assumptions:
The data is stored on the seventh sector of the fifth track of the disk:
the head will first swing to the fifth track, and then wait for the seventh sector to turn around. Data can only be read when the seventh sector turns to the bottom of the magnetic head.
This is the working principle of the mechanical hard disk, and it is precisely because the mechanical hard disk uses magnetic pole particles to store data, so the mechanical hard disk is often called a magnetic disk.
Next, let's look at the principle of solid state drives.
The working principle of solid-state hard disk is completely different from that of mechanical hard disk. Solid-state hard disk adopts pure electronic structure .
2 How solid state drives work
The basic unit of a solid-state hard disk to store data is called a floating gate transistor . The basic structure includes: a floating gate layer for storing electrons, a control electrode G, a substrate P, a source D, and a drain S.
We count the number of electrons in the floating gate layer as 0 if it is higher than a certain value, and as 1 if it is lower than a certain value.
How does a solid state drive work? Then look down~
data input
When writing data, a high voltage needs to be applied to the control electrode G, so that electrons can pass through the tunneling layer and enter the floating gate layer. Because of the existence of the insulating layer, the electrons can no longer move forward and are trapped in the floating gate layer. gate layer.
And when we remove the voltage, these electrons will still be imprisoned in the floating gate layer, because the tunneling layer is essentially an insulator, so the electrons can only be imprisoned, so that one bit of data is stored in it.
How long these electrons can be "imprisoned" is the number of years that the solid state drive can store data. Generally, a new solid state drive can store data for 10 years. Because over time, electronic "jailbreaks" continue to succeed.
When there are a certain number of "jailbreak" electrons, the data we saved will disappear.
erase data
When we erase the data on the solid-state drive, we are actually releasing these poor electrons, that is, applying high voltage on the substrate, so that the electrons are sucked out and the information is erased.
Through the above description, we understand the process of writing and erasing data.
So how to read the data?
read data
The principle of reading data is also very simple.
When there are no electrons in the floating gate layer (stored data is 1), we give the control stage a low voltage. Due to the low voltage, electrons can only be attracted to the position close to the tunneling layer, but cannot pass through the tunneling layer, so the source The drain can be turned on to form a current.
If a current is detected, then it is not storing electrons, and the read data is 1.
When there are electrons in the floating gate layer (stored data is 0), we also give the control electrode a low voltage. Since the electrons in the floating gate layer have a repelling effect on these electrons, the electrons cannot be attracted to the position close to the tunneling layer. The source-drain will not conduct and no current will flow.
If the current cannot be detected, it means that the floating gate layer stores a certain amount of electrons, and the read data is 0.
Countless floating-gate transistors can store a large number of 0 and 1 when stacked together. They are like bookshelves in a library, storing unlimited 0101 data.
Compared with the mechanical structure of the mechanical hard disk, the pure electronic structure of the solid-state hard disk has very prominent advantages in terms of access speed.
Before the mechanical hard disk reads data, it needs to swing the head arm above the corresponding track, and then wait for the corresponding sector to turn around.
Although most of the current mechanical hard drives are 7200 rpm or 5400 rpm, which seems to be very fast, but these two operations will still cause a delay of about ten milliseconds.
This delay is really insignificant for humans, but for computer memory and CPU, it does have a significant impact.
The solid-state hard drive is electronically interactive throughout, and the speed of electronic signals is far faster than the mechanical structure of the head arm and disk.
If your data is randomly scattered in all corners of the disk, the mechanical hard disk needs to go through multiple seeks and addressing, and wait for the sector to rotate under the head many times, so when the mechanical hard disk reads scattered files, the performance It is very weak and slow, that is, the random read and write performance is low.
Finally, there is a small question to test everyone:
Two solid-state drives of the same model, with a capacity of 1TB and a capacity of 500GB, which one has a longer service life and why?
Welcome to answer in the comment area~~~