Shulou(Shulou.com)11/24 Report--

Today, with the continuous progress of science and technology, computers have long come into our lives as a productivity tool. Everyone must have encountered the problem of slow start-up and stutter. If you look up the solution on the Internet, you will always see someone suggest changing the computer to a solid-state hard drive. So you go to the shopping software to search the solid state drive, and what comes into view is SATA, M.2, PCIe, AHCI, NVMe.

What do these parameters mean? Through these parameters, how to choose a suitable solid state disk from a dazzling array of products? Today, we will bring you a little popular science about the buses, protocols and interfaces of solid-state drives, so that you can become an "old driver" of solid-state drives in a second.

Bus (BUS) bus is the path of data exchange between different functional components of a computer. For SSDs, bus is the way data is sent from SSDs to CPU.

The bus is based on physical criteria, so its carrying capacity has a certain upper limit.

The total amount of data transmitted by a bus per unit time is called bandwidth.

There are three kinds of buses of solid state disk: SATA bus, PCIe bus and SAS bus. Their transmission rate and bandwidth data are shown in the following table.

(the commonly used rate unit of the transmission bandwidth of the PCIe bus indicates that X is a multiple of X1.)

The data in the above table is a little complex, and the SAS bus is often used for servers and will not be discussed. SATA3.0, PCIe3.0 and PCIe4.0 bus are often involved in our life. To give a simple example, when a car is driving on the road, there are three roads: SATA3.0, PCIe3.0, and PCIe4.0, as shown in the figure below.

It can be seen that at the same time, the SATA3.0 bus transmits the least traffic, just like a country road. PCIe3.0, PCIe4.0 bus transmission of more vehicles, is two more spacious roads, of course, PICe4.0 this road is wider.

In short, in terms of data transmission rate performance, we can simply understand that PCIe4.0 is the eldest brother, PCIe3.0 is the second brother, and SATA3.0 is the younger brother.

Protocol protocols are the rules agreed upon by both parties to communicate, including how to connect, how to identify each other, etc.

If two electronic devices want to transmit data effectively, they must have the same protocol or compatible protocols.

Efficient protocols require hardware support

There are three protocols involved in SSDs: AHCI protocol, NVMe protocol and SCSI protocol. The SCSI protocol is commonly used on the server and is not expanded here. The protocols often involved in solid state drives in life are AHCI and NVMe, and their specific principles are more complicated. Here, we still take the vehicle driving on the road as an example to explain. AHCI protocol is equivalent to a speed limit 30 sign, while NVMe is equivalent to a speed limit 60 sign.

As shown in the figure above, the AHCI protocol can be used for both SATA and PCIe buses. At this time, although the path represented by PCIe bus is "wider", due to the limitation of AHCI protocol, the speed improvement of PCIe bus is limited compared with SATA bus.

NVMe protocol can be used in PCIe bus. With the "high speed" NVMe protocol and the "wide" PCIe bus, the data transmission rate is greatly increased.

In a word, in terms of data transmission rate performance, we can simply understand that NVMe protocol is faster than AHCI protocol.

Interface (Interface) interface is the bridge between hard disk and motherboard

Interface, bus and protocol complement each other in solid state disk products. The theoretical rate limit of solid state disk interface can be judged by the carrying capacity of the bus.

The actual speed of the interface is also related to the use of materials and technology.

The following figure summarizes the common solid state disk interfaces and the corresponding protocol buses.

What is noteworthy in this table is:

PCIe can be used not only as bus to carry data information, but also as interface. As an interface, it is called a PCIe slot

SATA bus can only use AHCI protocol, while PCIe bus can use AHCI, NVMe and SCSI protocols.

For M.2 interface, it is divided into B&M-Key interface and M-Key interface, their appearance often has the difference of gap, usually there is a gap on the left and right sides of B&M-Key hard disk, while the solid-state disk gap of M-Key interface is on the right. But what we need to pay special attention to is that the type of M.2 interface can not be judged simply by the position of the gap shape.

Summary Today, we introduce the concepts of bus, protocol and interface of solid state disk.

The data transmission ability of PCIe bus is stronger than that of SATA bus.

The transmission speed of NVMe protocol is higher than AHCI protocol.

Different interfaces have matching buses and protocols, and the theoretical speed of the interface can be judged by the bus type.

So how to buy a solid-state hard drive that suits your computer? Once you know these concepts, here are three steps to tell you the solution

Step1: learn about the interfaces and protocol types supported by your computer motherboard

Step2: check the bus types supported by your computer interface according to the table summarized above

Step3: find the SSDs that meet the index relationship and choose them according to price and actual needs.

The above selection method is how to choose a solid state disk that matches your own computer. in fact, the actual transmission speed and quality of the solid state disk are also related to the following concepts:

Sequential reading and writing speed & 4K random reading and writing speed

Flash memory particle quality

Caching

Hard disk master control

This article comes from the official account of Wechat: ZTE documents (ID:ztedoc)

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