Why SSDs use PCI-E interface
It has been more than 60 years since the development of computers. As people's requirements for storage speeds continue to increase, the storage media has changed dramatically from the initial punch cards to the current SSDs. Nowadays, more and more high-end SSDs are beginning to be selected. PCI-E interface to connect the SSD to the motherboard to improve read/write speed.
As an ordinary user, should we choose high-end PCI-E SSD or SATA SSD? What is the difference between the two? So in this article, the author will introduce in detail the advantages and disadvantages of PCI-E channel SSD and PCI-E channel SSD. Let everyone know what to do when installing SSDs, buy on demand.
Why use PCI-E channel?
So why should the SSD be discarded from the SATA 3.0 interface and use the PCI-E interface? Let's first look at how the two interface hard disks work:
In the traditional SATA hard disk, when we perform data operations, the data will be read from the hard disk to the memory first, and then the data will be extracted to the CPU for calculation. After the calculation, the data will be written to the memory and stored to the hard disk; PCI-E is not the same The data is directly connected to the CPU directly via the bus, close to the maximum transfer speed, and the maximum amount of data, eliminating the need for memory to call the hard disk.
Simply put, we can understand the two channels into two identical cars, The PCI-E channel car is like driving at high speed, while the SATA channel car is like driving on a rugged mountain road Which speed do you say?
Different Interface SSD Speed Meters
From the above figure, we can see that the current mainstream SATA 3.0 channel has a maximum transmission speed of 6Gbps, and the actual maximum speed is 560MB/s. The SATA channel can no longer meet the growing read/write speed of the SSD, so the PCI-E SSD Came into being.
However, some readers may have questions about why my SSD is an M.2 interface, but the speed is not fast?
M.2 was originally called NGFF and its full name was Next Generation Form Factor. This interface is very special. It supports both SATA and PCI-E channels. It is very easy to misunderstand.
In fact, not all M.2 SSDs read and write speeds are very fast. If you use an SATA channel M.2 interface SSD, the read and write speed will not exceed 550MB/s.
To be careful of, Some of the motherboard manufacturers' M.2 interfaces have selected the native PCI-E channel of the CPU, and some have been extended through the PCH south bridge. This may affect the speed of the SSD.
2PCI-E protocol and speed advantages
AHCI and NVMe protocols
After talking about the interface, let's talk about the two solid-state drive protocols. It's as if the IDE is always on its way and AHCI seems to have a bottleneck.
The SATA interface and AHCI standard used today are actually designed for high-latency mechanical hard disks. Currently mainstream solid-state hard disks still continue to use them. Early solid-state hard disks may not have any problems with low performance, but with the performance of solid-state hard disks. Increasingly, these standards have become a major bottleneck in limiting solid-state drives. The AHCI standard designed for mechanical hard drives is not very suitable for low-latency solid state drives.
Picture from internet
One of the advantages of NVMe is low latency. This is mainly due to the streamlined memory stack. NVMe can issue commands without reading registers. Each AHCI command needs to read 4 non-cacheable registers, resulting in an additional delay of approximately 2.5μs.
The advantage of low latency and good parallelism is that it can greatly improve the random performance of the SSD, and it can play an excellent speed at any queue depth.
NVMe's IOPS performance on SSDs is also relatively large. Because the idea of parallelism was not fully incorporated into the specification when the AHCI specification was developed, the transmission capabilities can be optimized using the NCQ function, but the interface does not allow the SSD to truly maximize its parallelism.
In addition, for mobile device users, the use of NVMe storage devices can greatly help battery continuation. NVMe joins automatic power state switching and dynamic power management functions. The device can be quickly idle after 50 ms of energy consumption. Switch to energy consumption state 1 and enter the lower energy consumption state after 500ms idle.
Although switching energy consumption will cause a short delay, the power consumption under these two conditions when idle can be controlled at a very low level. Therefore, compared with the mainstream SATA interface solid-state drives, it also has a greater advantage in energy consumption management. .
Speed comparison
Here we look at the speed comparison of two solid state drives:
The left picture shows the SATA solid state drive, and the right picture shows the PCI-E solid state drive.
The gap between the speed of AS SSD running between the two is obvious. Whether it is continuous reading and writing, or 4K testing, PCI-E solid state drives are far ahead of SATA solid state drives. Overall score PCI-E solid state drives are more than three times higher than SATA solid state drives.
How to select ordinary users when installing
Having said so much, some readers may be confused. In order to help everyone understand, the author draws various interfaces and speed comparisons into tables so that they can be seen at a glance.
Different Interface SSD Protocols
Purchase suggestion:
Seeing this you may find that PCI-E has many benefits, but not everyone is suitable for purchase. Because of PCI-E SSD flash memory particles and mastering reasons, PCI-E SSDs are very expensive.
Such as 512GB SATA protocol SSD price is about 800 yuan, while the same capacity of the PCI-E protocol SSD price is as high as 2,000 yuan.
In addition, PCI-E will occupy the bus channel, and the entry and mid-end platforms have fewer CPU channels. They are not suitable for adding PCI-E SSDs. Only flagship platforms such as Z270 or X99 can fully utilize PCI-E SSDs. Performance.
