How to buy SSDs?

Source:   Editor: Ella Maclin Update Time :2019-10-18

How to buy SSDs?

The SSD can really affects the computer’s operation speed in some extend, but many people fell puzzled that whether we can make the best use of the SSD, or how much speed can SSD improve. Today, we will talk about how to use the SSD and how to buy it correctly.

Firstly, we will interpreter some nouns about the SSD, which are SATA、M.2、NVMe、PCI-e and AHCI.

Because the SSD should insert to the motherboard, the SSD has interface. The most commonly used interface are SATA and M.2.

SATA and M.2 are just like the entrance of highway. When the SATA is narrow, the throughput is also greatly limited. When M.2 is wider, the throughput is more.

But just the entrance can not decide the speed, the speed is also limited by the width of the following road. When the highway is wider, the more cars can pass at the same time that is the data transmission speed is faster.

The SSD entrance is also called SATA channel, which is relatively narrow and has a theoretical transmission bandwidth of 6 Gbps. In other words, it can reach 768mb / s in theory when using the SSD to test the reading and writing speed, but it can only reach 520mb / s actually.

The M.2 port can be compatible with SATA channel and has faster PCI-e channel.

Just like Samsung 970 EVO 250G, whose interface type is PCI-e Gen 3.0 x4. Which means that it has a theoretical transmission bandwidth of 32 Gbps. It can reach 4000MB/ s in theory when using the SSD to test the reading and writing speed. Which is considerably faster than SATA, but it can only reach 3200MB / s actually.

We have already known about SATA, M.2 and PCI-e, then what are NVMe and AHCI?

You can not move ahead fast just with the entrance of highway and road.

The transport protocols that is NVMe and AHCI decide the speed. The transport protocol is just like the speed limit sign in highway.

The SATA interface has no choice, it only has one channel. Therefore, its speed is limited in around 520MB/s.

Though M.2 has PCI-e channel. When the product you bought can’t support, the speed of M.2 can not reach 3200MB/s. Because the speed in SATA is limited in 500MB/s.

If you want to get faster speed, you must go in from the M.2 gate then go in the direction of PCI-e and support NVMe. At this time, the speed is fastest. Let’s sum up with product examples.

Toshiba Q200EX series 240G with 54$.

Type: M.2 SATA

Interface Type: SATA

Sequential Read Speed: less than 550MB/s

Sequential write speed: less than 510MB/s

Samsung 970 EVO 250G with 95$.

Type: M.2 PCIe Gen3.0 x4

Interface Type: NVMe 1.3

Sequential read speed: less than 3400 MB/s

Sequential write speed: less than 1500MB/s

These two products with the similar capacity, but the speed and price is very different. This is why the speed doesn’t improve even slower after using the SSD. If you want to have fast speed, M.2 +, PCI-e + and NVMe should be equipped completely.

Isn't it a little surprising? When buying the SSD , You don’t think that the speed is faster after using it. In fact, the difference between good SSD and ordinary SSD is much larger than you think. Some computers or mobile phones obviously have similar parameters, but the price is much different. The reason is that SSD or flash memory is just one of the factors.

Why my SSD becomes slower.

There are many factors affecting the speed of SSD, but the most obvious factor is the capacity of SSD.

This is the comparison of basic parameters of Samsung SSD with the same type and different capacity. We can find that the sequential read speed of two different capacities is about 3400MB/s, but the sequential write speed is obviously different with the speed gap of 800MB/s. Therefore, the capacity can obviously affect the speed.  

In fact, there is no deep principle in it. We still use the schematic diagram to explain it.

The SSD data are stored in memory chips. There are four chips in SSD with 250G capacity, the data can be put in these four chips when writing data. There are eight chips in SSD with 500GB capacity, the data can be put in theses eight chips. So the speed is certainly faster, even if it is less than double, it will be about 70% faster.

What I said above is to write on four or eight chips at the same time. It means the new SSD, if it has been used? The answer is the speed is going to be faster and faster.

Let's look at the figure above. When your SSD starts to store things, as more and more things are stored, the number of chips that can be written at the same time decreases. So the speed decreases dramatically. When your SSD is almost full, the speed may not be faster than that of the mechanical hard disk.

Therefore, we can put some unnecessary things into mechanical hard disk, when using laptops with 128G SSD. And we can put some necessary applications into SSD like Media Editor and games to saving more space and improve speed.

We evaluated a game book before. Its hard disk reading speed is good. Although it's not a top-notch game book, it's at least much better than those so-called game books with the speed of 400MB/s to 500MB/s.

It seems to have taught you how to discriminate SSD . It's still intuitive to measure the parameters of the hard disk with the method taught you today. The above test software is called AS SSD, which is easy to understand.


The aim of the passage is to tell you that the factor affecting SSD speed is not just only capacity. If you really understand this passage, you may get the answer of those questions of speed that bother you all the time.

In addition, if you want to update your laptop or desk computer, you can change SSD, which is the most effective and economical solution in theory.

I suggest you can collect this article, you can use it sooner or later.

If you don’t want to read the passage, you can remember these three words.

1.The speed of M.2 supporting NVMe is fastest, that is PCI-e.

2.The space of hard disk is larger, the write speed is faster.

3.The speed is slower, when the hard disk space is fuller.

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