Finding the Best M.2 SSD Drive
Under the hoods of the newest, skinniest laptops (and in the hollows of the latest PC motherboards), solid-state storage is undergoing 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) are migrating 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’re picking 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 need 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 are still a thing. (Samsung, for one, in spring 2015 released an mSATA version of its popular SSD 850 EVO). They remain on the market primarily because some laptop models of relatively recent vintage adopted the form factor, and residual demand exists there as capacity upgrades. But it’s definitely yesterday’s form factor, and mSATA saw only limited adoption on desktop systems. The exception is the subclass of mini-PCs made by companies such as Zotac and Gigabyte. Some of their Zotac Zbox and Gigabyte Brix mini-PCs, respectively, made use of mSATA slots to keep down the size of these tiny PCs.
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.” As it took shape, 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.
M.2: The Form Factor vs. the Bus
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.
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-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 (“M.2-2280”) and 60mm (“M.2-2260”). 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. The desktop motherboards we’ve used and seen with 22mm-wide M.2 slots have had 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. 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, of course, 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 512GB, though 1TB M.2 SSDs are now seeing the light of day. The typical capacity waypoints are 120GB or 128GB; 240GB, 250GB, or 256GB; and 480GB, 500GB, or 512GB. (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 25 to 75 cents per gigabyte (or more for the very highest-capacity drives), 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 chassis-enclosed bigger brothers. Many 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 same inner pathways inside the computer once it leaves the drive.
That’s not to say that’s a bad thing. Especially in the case of laptops, a machine might support only M.2 SATA-bus SSDs, and that will be the extent of your upgrade path…end of story. As a result, the only reason you’d upgrade the drive, in that situation, would be to get more capacity.
A few lean, premium laptops can make use of PCI Express-bus M.2 SSDs. (Many recent desktop mainboards with M.2 slots also support PCI Express M.2 SSDs.) 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.
Until a year or so ago, most of these 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 next-generation PCI Express x4 paired with a technology called NVMe (Non-Volatile Memory Express) to propel performance even further, especially with heavy, deeply queued workloads.
NVMe is another technical hurdle, because systems and motherboards need board-level support for these drives to be bootable. Many recent motherboards based around Intel’s Z170 chipset support PCI Express x4 NVMe M.2 drives. Gigabyte’s GA-Z170X-UD5, for one, was an early board that actually had two such connectors, and we’re seeing that more and more with late-model mainboards. But outside of new motherboards, these high-bandwidth, NVMe-capable connectors are still quite rare. 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.
Speaking of PCI Express x4 M.2 drives that support NVMe, those are getting more common. We’ve tested a growing number at this point, starting with the Samsung SSD 950 Pro in 2015 and its follow-up, late 2016’s Samsung SSD 960 Pro, as well as the lower-cost (and nearly as fast) Samsung SSD 960 EVO. Within that stretch, we also tested the Plextor M8Pe M.2 NVMe. These are indeed impressively fast drives, leaving the fastest SATA-based drives far behind. But apart from the aforementioned motherboards, and a slowly growing number of cutting-edge premium laptops and convertibles, few devices currently support these drives, or support them at their maximum speeds. So, as we said in the previous paragraph, make sure that your system supports this drive type 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.
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. Again, 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 Plextor (in the Plextor M6e PCI Express Black Edition) and Kingston (in the HyperX Predator PCIe SSD). Asus also offers an M.2 “carrier card” like these makers use. In essence, these products put your M.2 drive on a PCI Express expansion card and let you tap their speed (PCI Express 2.0 x2 or x4, today) through the PCI Express slots in a PC that lacks an M.2 slot. We actually like these because, at least in the case of the Plextor M6e PCI Express Black Edition, you get a heat sink on the M.2 drive. Some PCI Express-bus M.2 SSDs can run hot under sustained read/write loads, 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.
Shopping for an M.2 Drive Upgrade or Boot Drive
Welcome to the cutting edge! You’re shopping for a kind of drive that most 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.
CHECK THE PHYSICAL SIZE: 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.
KNOW WHICH BUS YOU’RE ON: 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 a 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 motherboards support either SATA-bus or PCI Express-bus M.2 drives. Others support only SATA, still others support only PCI Express. (And, in the case of PCI Express M.2, not all motherboards support PCIe x4.) You need to know what your board is optimized to use. All else being equal, PCI Express should give you a speed boost over a SATA model.
CHECK FOR BOOTABILITY: If you’re installing an M.2 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.
COMPARE THE COST PER GIG: 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. Divide the price (in dollars) by the capacity of the drive (in gigabytes) to get the cost per gig. For example, a 500GB drive that’s selling for $199 works out to about 40 cents per gigabyte. Use this as a value yardstick.
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.