Under the hoods of the newest, skinniest laptops (and in the hollows of the latest desktop-PC motherboards), solid-state storage has undergone a transformation. Even if you’re a close observer of all things tech, it’s understandable if you didn’t even realize it was happening.
That’s because the whole idea is to make the storage hardware itself close to invisible. Solid-state drives (SSDs) have largely migrated from the slab-like shapes of familiar hard drives into little sticks of memory that offer much the same capacities. And, in some cases, they have picked up speed along the way.
The traditional SSD that you buy and install in a desktop PC, or in place of a hard drive in a laptop, uses what’s known as the “2.5-inch drive” form factor. (In actuality, the drives are about 2.75 inches wide.) These SSDs have the same dimensions that laptop-style hard drives do. SSD makers adopted this standard size to make SSDs compatible with existing laptop designs. (They could configure laptops with the choice of a hard drive or an SSD without any retooling.) Desktop PCs, meanwhile, could accommodate SSDs of this size with little fuss. You could mount them in a 3.5-inch drive bay using a simple bracket. Over time, too, desktop PC chassis have evolved to gain their own bays and mounting points for 2.5-inch drives.
However, from an engineering point of view, SSDs didn’t to be that big. The enclosure an SSD comes in has a lot of dead space inside. It’s designed in that 2.5-inch size and shape to make the drive fit into those existing bays. So when mobile-device designers, challenged with slimming down laptops and tablets, reassessed this issue, the consensus was clear: The bulky 2.5-inch form factor, eventually, would have to go.
At the core, an SSD is just a thin circuit board studded with flash-memory and controller chips. Why not design around that?
In the Beginning, There Was mSATA…
The first attempt was a new form factor called mini-SATA, or mSATA. The boiled-down essence of an SSD with the shell removed, an mSATA drive is a bare, rectangular circuit board. (Most mSATA drives relevant to upgraders measure about 1×2 inches.) mSATA drives fit into a special slot in a laptop’s logic board or on a PC motherboard. As the name suggests, the slot is a conduit to the Serial ATA bus in the system. The interface on the drive end is an edge connector on the PCB, as opposed to the usual SATA cabling. The mSATA drive also draws all the power it needs through the slot.
By being reliant on SATA, mSATA drives gained all of the advantages and limitations of that interface, including the upper speed limit of SATA 3.0, the latest revision of Serial ATA. That’s not a bad thing, mind you. mSATA was also unusual in that it piggybacked on an existing connector, known as Mini-PCI, often used for installing small onboard components such as compact Wi-Fi cards.
Now, mSATA drives still linger on the market, primarily because some laptop models adopted the form factor years back, and residual demand exists as capacity upgrades. But it’s definitely a fading form factor, and mSATA saw only slight adoption on desktop systems.
Even in mSATA’s heyday, though, a replacement was in the works. During development, it was known by the prosaic name NGFF, for “Next-Generation Form Factor,” which still lingers. As it took shape, though, it took on its current, final name: M.2. The drives would be smaller, potentially more capacious, and, most important, not necessarily reliant on SATA.
So, What Is an M.2 SSD?
M.2 drives are as utilitarian as upgrades come: They look like sticks of gum studded with NAND modules and a controller chip. (“NAND” is the generic term for the flash-memory chips that make up the actual storage on the SSD; the term refers, technically, to the type of logic gates used in the underlying memory structure. See our primer Buying an SSD: 20 Terms You Need to Know for more SSD lingo explained.)
The key thing to remember about M.2 is that it is a form factor, a shape. The bus—the data pathway over which the data travels to and from an M.2 drive—is distinct from M.2 itself and can vary. And it can make all the difference.
But first, the shape issue. Any M.2 drive you are looking at will be labeled with a four- or five-digit number as part of its specifications or model name. It’s a measurement, in millimeters: The first two numbers define the drive’s width, the second two the length.
The market has settled on 22mm wide as the standard for desktop and laptop implementations; the aftermarket drives available and the accessible slots we’ve seen have all been that width. The most common lengths we’ve seen are 80mm (“Type-2280”) and 60mm (“Type-2260”). The lengthier the drive, the more NAND chips you can tend to stuff on it (plus, M.2 drives can be single- or double-sided), though know that length isn’t an absolute measure of capacity.
Now, why does length matter? Fit, especially in the case of laptops. Most desktop motherboards with M.2 slots have screw-mounting points for several lengths of M.2 drive (usually, 80mm, 60mm, and 42mm), so length hasn’t been an issue there. But it’s a different matter in a laptop with a user-accessible M.2 slot. The bay may be space-limited to M.2 drives of a certain size, or to only single-sided modules, if the thickness tolerances are really tight. You’ll want to check the space available before you shop.
As we mentioned, M.2 drive length isn’t always an indicator of drive capacity, but there are limits to NAND-chip density and how many memory modules engineers can stuff onto a PCB of a given size. As a result, most of the M.2 drives we’ve seen to date have topped out at 2TB, though you can find a few 4TB and 8TB models at lofty prices. The typical capacity waypoints are 120GB or 128GB; 240GB, 250GB, or 256GB; 480GB, 500GB, or 512GB; 960GB or 1TB; and 2TB. (Smaller-capacity 32GB and 64GB M.2 SSDs are also available for use in embedded applications or for SSD caching, but these will be of only marginal interest to upgraders or PC builders.) Pricing on these drives ranges anywhere from 10 to 75 cents per gigabyte, and the biggest factor affecting price is the bus type of the drive.
Now, to reiterate an important point: A drive may come in the M.2 form factor, but that says nothing about the bus that it makes use of. Determining that is just as important as making sure it fits.
The Bus-Interface Issue
This is the trickiest part of an M.2 upgrade. Most of the early M.2 drives were really just ordinary SATA drives stripped down to their fundamentals: a bare circuit board with a different physical connector, but at heart the same drives as their 2.5-inch bigger brothers. Some of them still are. You won’t see substantially better performance with these M.2 SATA drives versus their 2.5-inch SATA equivalents, because ultimately your data is traveling along the exact same inner pathways inside the computer once it leaves the drive.
That’s not a bad thing. Especially in the case of laptops, a machine might support only M.2 SATA-bus SSDs, and that will be the boundary of your upgrade path…end of story. As a result, the only reasons you’d upgrade the drive, in that situation, would be to get more capacity, or if the old one failed.
Nowadays, though, many lean, premium laptops can make use of PCI Express-bus M.2 SSDs. (Just about all new desktop motherboards with M.2 slots also support PCI Express M.2 SSDs, too.) With these, you may see a substantive increase in performance in benchmark testing, but in most real-world usage, they’ll just feel like a fast, premium SATA SSD.
The earliest versions of M.2 PCI Express SSDs made use of the PCI Express Gen 2.0 x2 interface, which defines a throughput ceiling that’s higher than SATA 3.0’s, but not enormously so. That’s changed. Most new, high-end M.2 drives, nowadays, support what’s called PCI Express Gen 3.0 x4, paired with a technology called Non-Volatile Memory Express (NVMe) to propel performance even further, especially with heavy, deeply queued workloads.
Beyond that is PCI Express 4.0. We’ve tested a few SSDs that support the newer 4.0 version of the bus, and the read and write speeds for a few (such as Samsung’s flagship SSD 980 Pro) are rated as high as 7,000MBps. These drives are a peek at the future, but for the moment PCI Express 4.0 is supported only on desktop systems employing the AMD X570 and B550 chipsets (for mainstream Ryzen) and the AMD TRX40 (for third-generation Ryzen Threadripper). You can use these PCIe 4.0-based in Intel-chipset systems, but they’ll just bounce down to slower PCIe 3.0 speeds.
Meet NVMe: The Speed Booster
NVMe is another technical hurdle, because systems and motherboards need board-level support for these drives to be bootable. Here in 2020, almost all late-model motherboards now support PCI Express 3.0 x4 NVMe M.2 drives, but older boards are not guaranteed to support booting from an NVMe-based drive. Outside of new motherboards, these high-bandwidth, NVMe-capable slots are also found in some recent laptops. Also note that in some cases, a laptop may support a PCI Express NVMe drive, but it may be soldered to the motherboard and thus not upgradable. So, if you’re thinking of upgrading a recent laptop or convertible, be sure to consult your manual very closely before buying one of these drives.
Among M.2 drives, PCI Express x4 M.2 drives that support NVMe are increasingly the norm among aftermarket purchases. We’ve tested a growing number, led by Samsung’s field-leading and pioneering SSD Pro and SSD EVO families. Ever since those Samsung drives pioneered the way, though, we’ve also seen fine NVMe-capable models from ADATA, Seagate, WD, and many others.
These are indeed impressively fast drives, leaving the fastest SATA-based drives well behind. But know that they are more relevant for PC builders or folks upgrading very recent systems rather than older PCs, which may not have an M.2 slot, or may have an M.2 slot but not one that supports PCI Express and/or NVMe—only SATA-based M.2. So, as we said in the previous paragraph, make sure that your system supports this kind of drive before picking one up. You don’t want to bring home one of the fastest consumer drives available, only to find your system won’t boot with it installed.
Basic Compatibility, Card-Based M.2, and Optane Memory
Okay, back from Planet NVMe. Today, the real choice if you’re M.2-shopping will be between basic SATA and PCI Express M.2 drives, and for most users, those options will be dictated simply by what your motherboard or laptop can accept. A careful browse of support forums or a call to the vendor’s support line should unravel the M.2 bus-compatibility details. On the desktop side of the aisle, many recent M.2-equipped mobos support both kinds.
If you’re looking to upgrade a desktop but your PC’s motherboard doesn’t have an M.2 slot at all, one incidental option is what we call an “M.2 drive on a card.” We’ve seen solutions like this from storage stalwarts such as Intel, OWC, and Kingston. Asus and MSI also offer an M.2 “carrier card” like these makers use with some of their high-end motherboards. In essence, these products put your M.2 drive on a PCI Express expansion card and let you tap their speed through the PCI Express slots in a PC that lacks an M.2 slot. Some such cards support multiple M.2 drives, too. A few of the latest high-end AMD motherboards supporting PCI Express 4.0 even bundle such cards, supporting two or four M.2 drives, to supplement onboard M.2 slots.
We actually like these because often, you get a heat sink on the M.2 drive. Some PCI Express-bus M.2 SSDs can run hot under sustained read/write tasks and throttle their speed. That said, unless you’re running a server or something similar, where a drive is constantly getting hammered, that’s usually not something you have to worry about. That’s because many of these drives are so fast, they get their transfer duties done before they have a chance to get all that hot.
One last caveat to drop in before we get to our product recommendations surrounds Intel’s SSD line. Intel sells a family of M.2-based storage products under the brand name Optane. Know that there are two very distinct types of drives here, which may look identical. Intel’s Optane SSDs are SSDs like any other, bootable drives that can serve as a stand-alone boot drive or as secondary storage.
Intel’s Optane Memory, however, is a different animal. This is an M.2-format module that looks like an SSD, but serves as an accelerating cache for another drive, usually a hard drive. Again, these are not the same thing; if you’re buying an Optane drive, make sure you know what you are buying. You can read a lot more about Optane Memory in our deep-dive review of the first generation.
M.2 Upgrades and Boot Drives: What to Look For
Welcome to the cutting edge! You’re shopping for a kind of drive that many folks don’t even realize exists. As a result, you need to pay attention to several factors that may not be documented very well while you shop. Let’s recap.
Make sure the width and especially the length (expressed in millimeters) will work in the space available for the drive. (This is mainly an issue with laptops.) Most will be 22mm wide, but the length varies: 42mm, 60mm, 80mm, 110mm are the most common sizes.
In a laptop-upgrade scenario, you’re almost certainly swapping out one M.2 drive for another, with the intent of gaining capacity. Make sure you know the specifications of the drive coming out of your system—and whether it’s reliant on the SATA or PCI Express bus—so you can install the same, presumably roomier kind going in.
For a desktop, it’s a bit trickier. Some motherboard M.2 slots support either SATA-bus or PCI Express-bus M.2 drives on the same slot. Others support only SATA M.2 drives, still others support only PCI Express M.2 drives. (And, in the case of PCI Express M.2, not all older motherboards support PCIe x4 or NVMe!) You need to know what your board is able to use and buy accordingly. All else being equal, PCI Express should give you a speed boost over a SATA model, but for everyday tasks, a SATA SSD will serve just as well, and be indistinguishable in cases from a PCI Express one.
Also, with the very latest drives, look for PCI Express 4.0 support. You’ll want to have a compliant late-model AMD motherboard if you buy one of those.
If you’re installing an M.2 SSD in a desktop board for the first time, verify with the board maker that an M.2 SSD of the bus type you are considering will be bootable. Though unlikely, a BIOS upgrade may be necessary with an older motherboard.
Cost per gigabyte is the main yardstick whereby you can price-compare similar M.2 drives from different makers. Expect to pay more for PCI Express bus models, all else being equal, and more for PCIe 4.0 drives than PCIe 3.0 ones. But the cost differences are narrowing in both cases. Divide the price (in dollars) by the capacity of the drive (in gigabytes) to get the cost per gig. For example, a 1TB (1,000GB) drive that’s selling for $99 works out to about 10 cents per gigabyte. Use this as a value yardstick when looking at different drives.
So, Which M.2 SSD Should I Buy?
Below are the top M.2 solid-state drives that we’ve reviewed. You can also check out our roundups of the best external SSDs, as well as the best external hard drives for Mac, and the overall best external hard drives.
If you’re also interested in factoring larger 2.5-inch drives into the equation, check out our roundup of the best internal SSDs overall, which factors in 2.5-inch models. And if you want to see strictly PCI Express-based ones, see our roundup of the best PCI Express NVMe drives.
