NVMe drives are a big deal in computer storage right now, and for good reason. Not only does an NVMe solid-state drive (SSD) leave most older SSDs in the dust, it’s also blazing fast compared to standard 3.5- and 2.5-inch drives.
NVMe vs. SATA III
Take, for example, the 1 TB Samsung 860 Pro, a 2.5-inch SSD with a maximum sequential read speed of 560 megabytes per second (MB/s). Its successor, the NVMe-based 960 Pro, is more than six times faster than that, with a top speed of 3,500 MB/s.
This is because the pre-NVMe drives connect to a PC via SATA III, the third revision of the Serial ATA computer bus interface. NVMe, meanwhile, is the host controller interface for newer, more advanced SSDs.
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SATA III and NVMe are the terms most commonly used to differentiate between old-school drives and the new hotness everyone wants. NVMe is not, however, the same type of technology as SATA III.
We’ll get into why we use the terms “SATA III” and “NVMe” to compare the technologies later.
What is SATA III?
In 2000, SATA was introduced to replace the Parallel ATA standard that preceded it. SATA offered higher speed connections, which meant vastly improved performance compared to its predecessor. SATA III rolled out eight years later with a maximum transfer rate of 600 MB/s.
SATA III components use a specific type of connector to slot into a laptop, and a specific type of cable to connect to a desktop PC motherboard.
Once a drive is connected to the computer system via SATA III, the work is only half done. For the drive to actually talk to the system, it needs a host controller interface. That job belongs to AHCI, which is the most common way for SATA III drives to talk to a computer system.
For many years, SATA III and AHCI performed admirably, including during the early days of SSDs. However, AHCI was optimized for high-latency rotating media, not low latency, non-volatile storage like SSDs, a representative from drive manufacturer Kingston explained.
Solid-state drives became so fast, they eventually saturated the SATA III connection. SATA III and AHCI simply couldn’t provide enough bandwidth for increasingly capable SSDS.
With drive speeds and capabilities expanding, the search was on for a better alternative. And, luckily, it was already in use on PCs.
What Is PCIe?
PCIe is another hardware interface. It’s best known as the way a graphics card slots into a desktop PC, but it’s also used for sound cards, Thunderbolt expansion cards, and M.2 drives (more on those later).
If you look on a motherboard (see above), you can easily see where the PCIe slots are. They mostly come in x16, x8, x4, and x1 variants. These numbers indicate how many lanes of data transmission a slot has. The higher the number of lanes, the more data you can move at any one time, which is why graphics cards use x16 slots.
There’s also an M.2 slot in the image above, right under the top x16 slot. M.2 slots can use up to four lanes, thus, they’re x4.
The key PCIe slots in any computer have lanes connected to the CPU for the best performance possible. The rest of the PCIe slots connect to the chipset. This also supports a fairly speedy connection to the CPU, but not as fast as the direct connections.
Currently, there are two generations of PCIe in use: 3.0 (the most common) and 4.0. As of mid-2019, PCIe 4.0 was brand-spanking-new and only supported on AMD’s Ryzen 3000 processors and X570 motherboards. Version 4, as you would expect, is faster.
However, most components are not yet saturating the maximum bandwidth of PCIe 3.0. So, while PCIe 4.0 is impressive, it’s not yet a necessity for modern computers.
NVMe Over PCIe
PCIe, then, is like SATA III; they’re both used to connect individual components to a computer system. Just like SATA III needs AHCI before a hard drive or SSD can communicate with a computer system, PCIe-based drives rely on a host controller, called non-volatile memory express (NVMe).
But why don’t we talk about SATA III versus PCIe drives, or AHCI versus NVMe?
The reason is pretty straightforward. We’ve always referred to drives as being SATA-based, like SATA, SATA II, and SATA III—no surprise there.
When drive manufacturers started making PCIe drives, there was a short period during which we talked about PCIe SSDs.
However, the industry didn’t have any standards to rally around as it did with SATA drives. Instead, as Western Digital explained, companies used AHCI and built their own drivers and firmware to run those drives.
That was a mess, and AHCI still wasn’t good enough. As Kingston explained to us, it was also more difficult for people to adopt drives that were faster than SATA because, rather than a plug-and-play experience, they also had to install special drivers.
Eventually, the industry rallied around the standard that became NVMe and replaced AHCI. The new standard was so much better, it made sense to start talking about NVMe. And the rest, as they say, is history.
NVMe was built with modern, PCIe-based SSDs in mind. NVMe drives are able to accept vastly more commands at once than SATA III mechanical hard drives or SSDs. That, combined with lower latency, makes NVMe drives faster and more responsive.
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What Do NVMe Drives Look Like?
If you go shopping for an NVMe-based drive today, what you want is an M.2 gumstick. M.2 describes the drive’s form factor—or, for our purposes, how it looks. M.2 drives usually have up to about 1 TB of storage, but they’re small enough to hold between your thumb and index finger.
M.2 drives connect to special M.2 PCIe slots that support up to four lanes of data transfer. These drives are usually NVMe based, but you can also find M.2 drives that use SATA III—just read the packaging carefully.
SATA III-based M.2s aren’t all that common these days, but they do exist. Some popular examples are the WD Blue 3D NAND and the Samsung 860 Evo.