Comparison of the difference between solid state drive (SSD) and mechanical hard disk (HDD)

Source:   Editor: Sharpay Update Time :2019-01-13

    First, the evolution process

    From the moment that the computer was born, storage devices played an indispensable role. The original hard drives, such as the famous IBM RAMAC, were huge and heavy. Until around 1980, IBM introduced the thin-film magnetic head technology, which allowed us to bid farewell to those giants. Then we put more and more attention on storage density and speed, and certainly we did not forget the idea of pursuing smaller and more convenient. However, because of the innate design of the mechanical hard disk, we have to face many problems such as the stability and shock resistance of its mechanical components. In recent years, SSD, a new type of storage device has emerged, which has become a new star in the hard disk industry by virtue of its superior performance against HDD. But due to some controversy, it has not been able to shake the mainstream position of HDD in a short time.

    Second, the principle comparison of HDD and SSD

    (1) Principle of HDD

    HDD, is named as Hard Disk Drive, is one non-volatile storage device based on a hard rotating disk on the computer. It stores and retrieves digital data on a flat magnetic surface. The information is written to disk by changing polarity by electromagnetic current through a magnetic head close to the magnetic surface. At the same time, the information can be read in the opposite way, for example, when the read head passes over the recorded data, the magnetic field changes the electrical signal in the coil. It adopts random access to read and write, so the data in the hard disk can be read in any order. The inside of the HDD includes one to several high-speed rotating disks and a magnetic head placed on the cantilever of the actuator. According to its operating principle, it is easy to find that the modern mechanical hard disk works in the same way as its name, which is mechanically operated, that is, the electric motor drives the disk to rotate at a high speed, and then accesses data with the assistance of the operation of magnetic head.

    (2) Principle of SSD

    SSD, is named as Solid State Disk or Solid State Drive, is one computer storage device that use memory as a permanent storage. Although SSDs do not use "disc" to store data, nor do they use "driver" motors, people still called them as solid state drives or solid state drives according to naming convention. SSD can be divided into volatile and non-volatile. Here we focus on non-volatile SSD that is more suitable as the replacement for traditional hard drive. Data access in SSD is mainly implemented by NAND Flash and its master control chip, and there is no active mechanical component, which is absolute chip structure.

    Third, their respective advantages and disadvantages

    (1) Comparison of overall performance

    Advantage comparison chart of SSD and mechanical hard disk


Comparison of SSD and mechanical hard drive










Random access

Extremely fast


Times of write

SLC: 100,000 times / MLC: 10,000 times


Disk Array


Extremely difficult

Working noise



Operating temperature

Extremely low

More obvious

Shock resistance



Data Recovery




    (2) Comparison of reading and writing speed

    From the previous article, the HDD performs magnetic operation on the high-speed rotating disk by the magnetic head to read data, so the faster the disk rotates, the faster the read-write speed of mechanical hard disk is. At present, the mainstream mechanical hard disk platters in the consumer market mainly have two types of 5400 rpm and 7200 rpm, and the read-write speed under the SATA3 interface are about 50-90 MB/s and 90-190 MB/s respectively. It is easy to find that the impact of the increase in the speed of the HDD on its read-write speed is still very obvious. However, the rotation of mechanical hard disk depends on the driving of mechanical motor, and the increase in its speed will also cause problems such as heat generation and wear. It is still very difficult to greatly increase the rotational speed of the HDD with current available mechanical technology, so its read-write speed is also difficult to make a tremendous progress on the existing basis. On the contrast, SSD will not encounter the speed bottleneck of the HDD because it does not use any mechanical structure. At the same time, due to its chip-based flash memory access, the basic read-write speed is extremely fast. However, it should be pointed out that unlike most HDDs that the read-write speed is only related to the rotational speed, the read-write speed of SSDs is easily affected by various factors such as capacity and master control because of its special structure, so the range of change in read-write speed is also large. At present, the read-write speed of mainstream SSD is mainly concentrated in the range of 500MB/s to 1GB/s, and a few high-end models can reach more than 2GB/s. But no matter which model, it is an indisputable fact that the read-write speed of the SSD is higher than that of HDD. Because of the difference in the underlying technology, the read-write speed of the HDD can be said to have been lost at the beginning.