M.2 SSD vs. SATA SSD? Which One is the Best?


SATA SSD is an SSD with SATA (Serial Advanced Technology Attachment) interface. So far, SATA interface has three versions. The currently popular version is SATA III, which was published by Serial ATA International Organization (SATA-IO) in 2009.

SATA interface mainly uses AHCI (Advanced Host Controller Interface) protocol. The Throughput (Transfer Rate) value of SATA III is 6 Gb/s (600MB/s).

What Is M.2 SSD?

M.2 SSD is an SSD with M.2 interface. M.2 interface is also called Next Generation Form Factor (NGFF), which is a new generation interface standard tailored for Ultrabook to replace the mSATA interface. Compared with mSATA SSD, M.2 SSD has advantages of smaller size and better transmission performance.

M.2 interface has two types of forms: B-key (Socket 2) and M-key (Socket 3). B-key interface can support SATA bus standard or PCI-E3.0X2 bus standard, and therefore it may support AHCI protocol or NVMe protocol.

When it supports AHCI protocol, its throughput can only reach 6 Gbps at most. When it support NVMe protocol, its throughput can be up to 16 Gbps.

As for M-key interface, it only supports PCI-E 3.0X4 bus standard and NVMe protocol. The theoretical read-write speed can be up to 4 GB/s (32 Gbps).


SATA and PCI-E Bus Standard

A Bus is a common communication trunk that transmits information between various functional components (such as CPU, memory, hard disk, and various input and output devices) of a computer.

A hard drive Bus standard stipulates hard drive’s technical specifications like pin location, etc. Thus, manufacturers can produce hard disks according to the bus standards and specifications.

SATA Bus standard is an external bus standard for hard disk, which adopts serial connection mode to make the interface have advantages of simple structure, fast transfer speed, high execution efficiency, stronger error correcting capacity, and support for hot plug.

PCI-E Bus standard is an internal local bus standard, which is put forward to replace PCI (Peripheral Component Interconnect) bus. It is a high-speed serial point-to-point dual-channel high-bandwidth transmission.

PCI-E Bus standard mainly supports active power management, error reporting, end-to-end reliable transmission, hot plug, quality of service (QOS) and other functions. Above all, it has a very high transfer rate. PCI-E bus standard is superior to SATA bus standard in read-write speed.

bandwidth and transfer rate of different bus standards

However, the read-write speed is not only related to bus standard, but also is affected by data transfer protocols such as AHCI and NVMe.

AHCI and NVMe Protocol

AHCI and NVMe are data transfer protocols, which work above interface to determine data transfer method.

AHCI is a technical standard made by Intel Corporation, which stipulate a hardware mechanism that allows software to communicate information with SATA storage devices. AHCI can make SATA storage device activate advanced SATA functions such as support for 32 ports, elimination of master / slave handling, hot plug, etc.

In other words, AHCI protocol can realize the most potential of SATA interface. However, AHCI protocol is designed for traditional HHD, so it can’t realize the potential of SSD. Even if the M.2 SSD uses PCI-E bus, the read-write speed can’t still exceed 600 MB/s when it uses AHCI protocol. Hence, NVMe protocol comes out.

NVMe (Non-Volatile Memory express) protocol is first published in 2011. Compared with AHCI, it can reduce latency time greatly owing to no need for accessing register when giving a command.

Besides, it can support 64 queues and each queue can carry 64000 instructions, so that the IOPS ability is improved greatly. In a word, NVMe can extremely activate the potential of SSD.

bandwidth and transfer rate in AHCI mode and NVMe mode

Let’s make a conclusion. If an M.2 SSD only supports AHCI protocol, its read-write performance is same as that of SATA SSD. If an M.2 SSD uses NVMe protocol, its performance will be much better than that of SATA SSD. Therefore, if you want to buy an M.2 SSD, please pay attention to the data transfer protocol.

Switch from AHCI to NVMe Protocol

If you have installed an M.2 SSD in your computer, you should switch the data transfer protocol to NVMe. Here is a brief tutorial on how to change data transfer protocol in BIOS to improve computer performance.

Step 1: Restart your computer and follow the guide that appears on your computer to enter firmware. Please concentrate on your computer screen because that guide just appears for a short time.

Step 2: Please find an item with “Bus” or “SATA” and then change this item from SATA to NVMe Protocol.

To know more information about M.2 SSD vs. SATA SSD, please click the original text: M.2 SSD vs. SATA SSD: Which One Is Suitable for Your PC?

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