[TOPIC] Basic knowledge you want to know! Let’s understand speed and performance of HDD and SSD

Basically, HDDs and SSDs have been installed in a PC when you buy it. How much do users understand about this HDD and SSD? Although there is an understanding that stores data somehow, there may be many people who do not understand the transfer speed and the performance.
An HDD and an SSD are indispensable points for creating a comfortable personal computer environment. If you deepen your understanding of its speed and performance, you will be able to create more suitable personal computer environment.


  1. HDD and SSD storage capacity
  2. Performance related to HDD and SSD speed
    2-1. Number of platters (HDD only)
    2-2. Rotation speed (HDD only)
    2-3. Cache capacity (HDD / SSD)
    2-4. SSD type (SSD only)
  3. Conclusion

・1. HDD and SSD storage capacity
Regarding performance of HDD and SSD, a storage capacity is inevitable. If you want to handle a lot of files, or save music and videos on your computer and enjoy them, you need a large HDD and SSD capacity or an external HDD. Usually, an internal HDD are 500GB to 1TB, and SSDs are 240GB to 500GB. Please refer to the following to select the optimum storage capacity.

1TB = 1000GB

Photos / Images (4MB/1pcs) : 1TB = 250,000 pcs

Movies (720pixcels) : 1TB = 167 hours

TV recording: 1TB = 120 hours

・2. Performance related to HDD and SSD speed
Regarding the speed of HDD and SSD, the following points are greatly related.

・2-1. Number of platters (HDD only)
A platter is a magnetic disk inside an HDD that reads and writes data. In other words, the number of platters indicates how many magnetic disks are in an HDD. It is said that the transfer speed of a normal HDD is faster when the capacity per platter is larger. If the capacity per platter is small, the amount of data that can be read in one rotation is also small, therefore, a larger number of rotations is inevitably required. From that point of view, if there are HDDs that have the same capacity, the one with less platter can read and write more data in one rotation. That means the one has higher transfer speed than the other.

・2-2. Rotation speed (HDD only)
Example: 7200 rpm = 7200 rpm / 1 minute = 7200 rpm / 60 seconds = 120 rpm / 1 second

The rotation speed indicates how fast the platter rotates. It is expressed in units called Rpm, and the higher the number, the faster it is.

・2-3. Cache capacity (HDD / SSD)
The cache is a place to temporarily store the data to be written to an HDD or an SSD. The more data you write, the slower the data saving speed, since there are many data waiting to be saved. By temporarily saving them in a cache location, you can free up space on your computer and the speed become faster. In other words, the larger the cache capacity, the faster the processing can be performed even when writing a large amount of data.

・2-4. SSD type (SSD only)
There are three types of SSD: SLC (single level cell), MLC (multi-level cell), and TLC (triple level cell). SSD writes data to flash memory (flows it with electricity), and this data writing is classified according to how much information is stored in one cell. In terms of speed, SLC is the fastest, followed by MLC, and slowest is TLC.

・3. Conclusion
The performance of an HDD and SSD cannot be judged only by these capacity. The transfer speed also has a big influence on how comfortable you can handle your work on your computer. Of course, speed is very important not only when purchasing a personal computer but also when choosing an external HDD or SSD. The higher the performance, the higher the price of most products. It is important to determine the required performance in consideration of your own usage and environment.

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