Mainboard Slot M2

What's Best? U.2, M.2, SATA Express, & SATA

• ASRock updated its Fatal1ty branded socket AM3+ motherboard. The new ASRock 990FX Fatal1ty Killer gives AMD platform gamers most advancements in onboard connectivity. To begin with, the board is based on the AMD 990FX chipset, with SB950 southbridge. It draws power from a combination of 24-pin ATX a.
• GIGABYTE B450 AORUS PRO WIFI (rev. 1.0) AM4 AMD B450 SATA 6Gb/s ATX AMD Motherboard. Number of Memory Slots: 4×288pin; Memory Standard: Support for DDR4 3600(O.C.)/ 3466(O.C.)/ 3200(O.C.)/ 2933/ 2667/ 2400/ 2133 MHz memory modules; PCI Express 3.0 x16: 1 x PCI Express x16 slot, running at x16 (PCIEX16). Actual support may vary by CPU.

Below is the transcript for the video, which reads as a complete article for folks who prefer the written form:

Replacement M.2 Mounting Screw for M2 Size SSD's. Guaranteed fit for M.2 slot. Perfect for when you lost your motherboard or adapter’s M.2 screw. Package includes 2 screws. Please click the Thumbs up + button if I have helped you and click Accept as Solution if your problem is solved. The best performing Z390 ITX board is the Asrock Phantom, two M.2 slots, and a cut down TB3 port. The Strix is the more popular board based of name recognition probably but doesn’t overclock as well as the Phantom but has an integrated shield, two M.2 slots and supports 64GB of memory. Either one of these are really great choices for Z390 ITX. Another way to add a M.2 SSD to it is through a PCI adapter. However, this motherboard has only 2.0 PCI slots. The M.2 SSD is designed to perform best with 3.0 slots. Am I correct that a M.2 SSD will work in a PCI 2.0 slot? And if so, does the performance, though less than optimal, justify the upgrade, or should I invest in a new motherboard?

PAX East heralded a strong re-emergence of another new storage interface – this time, it's the U.2 interface that we saw on Gigabyte's unreleased Broadwell-E motherboards. This TLDR video recaps the differences between U.2 and M.2 storage devices as quickly as we can, with some additional information on SATA Express – like where it's gone.

First up, an extremely abbreviated recap of current chipsets: Intel's 100-series chipsets have high-speed IO lanes that are almost entirely addressable by the motherboard vendor, allowing for more differentiation between products. These are called HSIO lanes. Z170 has 26 HSIO lanes that can be assigned to GbE, SATA, PCI-e, or PCI-e enabled devices – like U.2 and M.2.

What is U.2? The U.2 interface was originally called SFF-8639, but has been renamed. The U.2 interface connects directly to PCI-e lanes on the motherboard, rather than going through the SATA interface, and that makes U.2 an expansion on SATA Express. U.2's pin-out allows use of 4 total PCI-e lanes. As such, its maximum theoretical throughput on Gen3 is 4GB/s. The U.2 pin-out resembles the SAS connector, but with way more pins for the lanes. Several of the pins are reserved for the refclock, lanes 0-3, the SMBus, and Dual Port. The remainder of the pins are used for signaling, power and control, and the other refclock.

(Above: Can't fit many of these on a motherboard).

(Above: A U.2 SSD)

On the motherboard, U.2 is a double-decker connector that receives a similarly double-decker cable from the SSD. On the other end, a much wider cable plugs into the SSD for the U.2 multi-lane interface, with an additional cable for power. This is the fastest 2.5” SSD interface currently available to consumers, but that doesn't mean the drives are inherently faster. More on that momentarily.

SATA Express, meanwhile, communicates maximally through 2 PCI-e lanes on the motherboard, limiting the interface to 2GB/s on Gen3. SATA Express will become a dead and abandoned standard in short order, as the industry continues to ignore its existence and moves fully to M.2 and U.2 interfaces. SATA Express cannot communicate through 4 PCI-e lanes.

For reference, SATA has a maximum theoretical throughput of 600MB/s, which comes down to about 550MB/s after the overhead is accounted for. SATA does not utilize PCI-e, which is a small advantage for anyone maxing-out their chipset's lane count – but keep in mind that chipset storage lanes are not the same as GPU lanes, so even multi-GPU configurations may not conflict with NVMe or PCIe SSDs. Depends on the configuration, though.

(Above: U.2 adapter for M.2 slots allows for connection to U.2 SSDs -- some of which use faster controllers than M.2 SSDs)

M.2, then, is the most comparable to U.2. It's capable of the same four-lane throughput for storage devices, but takes a significantly larger footprint on the motherboard and limits users purely by physical space. U.2 interests us because it can be stacked where current SATA connectors are, PCI-e lanes allowing, and you could theoretically run several 2.5” U.2 SSDs.

Host, Video Editing: Steve 'Lelldorianx' Burke
B-Roll: Keegan 'HornetSting' Gallick
Supporting Research: Patrick 'Mocalcium' Stone

Most solid-state drives released within the last year or so have been too fast for the bus they're connected to. The 6Gbps SATA III spec was finalized in the days when rotational hard drives still ruled and SSDs were rare, ludicrously expensive, and relatively unreliable.

There are a couple of different standards that have been created to solve this problem, and they both solve it in the same basic way. One, SATA Express, uses the same physical connector as older SATA drives but uses PCI Express lanes rather than the SATA bus to boost storage speeds. The other, which will be more common in space-constrained mini-desktops, all-in-ones, and Ultrabooks, is called M.2 (previously NGFF, for 'Next-Generation Form Factor').

M.2 is interesting not just because it can speed up storage with PCI Express lanes, but because it can use a whole bunch of different buses too; it stands to replace both mSATA and mini PCI Express, two older standards that have been used for SSDs and Wi-Fi cards in laptops for a while now. Intel's new Broadwell CPUs and their chipsets include native support for M.2 and PCI Express boot drivers—neither PCIe-connected storage (hi Apple) nor the M.2 connector itself are new, but beginning with Broadwell systems each of those two things will become much more common.

Let's start with the physical connector and the things that connect to it. There's a lot to unpack, starting with the fact that there's more than one kind of M.2 connector, more than one type of interface that can be used with M.2, and more than one kind of M.2 card.

Getting to know M.2

Pictured at the top of this article are four different M.2 cards. The one on the left is a combo Wi-Fi and Bluetooth card. The next one to the right is a Sandisk SSD that uses the SATA bus. The next one is an Intel SSD that also uses SATA. The one on the right is a Samsung SSD that can use up to four PCI Express lanes.

Pay attention to two things as you compare and contrast these cards. First, the physical connector on each card is different; each card has different cutouts in the bottom and exposes different pins. Second, the cards are of different lengths and widths. All of this is accounted for in the M.2 spec (PDF).

The different connectors signify different M.2 'module keys.' Each key exposes a different set of interfaces to each card—M.2 can connect directly to the PCI Express bus, but different pins can be used to connect to the USB 2.0 and 3.0 buses, SATA III, DisplayPort, and a variety of other less-prevalent storage buses. Cards with one notch at the bottom are keyed for one specific kind of connector. Cards with two notches can be used in two different kinds of connectors.

Above is a picture of two M.2 slots on the motherboard of an HP Stream Mini. The slot on the left uses module key E, and the one on the right uses module key B. The Wi-Fi card is keyed for slots A and E, so it fits in the left slot with no problems. The Intel SSD is keyed for slots B and M, so it fits in the right slot. The Samsung SSD is keyed for slot M, so it won't fit in either of the Stream's slots.

The table above lays out the keys in common use today—there are others, mostly placeholders to be called into service as newer buses and interfaces are introduced.

Note the four- or five-digit numbers paired with each slot. These are actually codes to refer to the physical dimensions of each card; the first two digits specify the width in millimeters and the second two or three digits specify the length. Our Wi-Fi module is 16mm wide and 30mm long, or 1630. Two of our SSDs are 22mm wide and 80mm long, or 2280. The other SSD is 22mm wide and 42mm long, or 2242. All motherboard slots are 22mm in width, even the ones attached to 30mm-wide cards.

All current keys can give cards access to two PCI Express lanes, but otherwise interface compatibility is all over the place—so far, it's been pretty easy to guess what kind of peripheral you're dealing with based on the key it uses. Wi-Fi and WWAN cards tend to use keys A and/or E, since they only need the PCI Express or USB 2.0 buses and only need 30mm in length to fit all their key components. SATA SSDs and SSDs that use two PCI Express lanes tend to use keys B and M to maximize compatibility, since both connectors can deliver both SATA III and two PCIe lanes. The very fastest SSDs tend to be M-keyed since it's the only one that delivers four PCIe lanes.

This is a lot to digest, but it's most of what you need to know to understand M.2. There are some other stipulations around the physical thickness of the cards that you can read about in the documentation, but they aren't as important to our discussion today.

Mainboard Slots

The key system isn't always foolproof—our A- and E-keyed Wi-Fi module will physically fit into the B-keyed SSD slot even though the computer won't recognize it there. M.2 is certainly more confusing than the mPCIe and mSATA specs, but in the end it's more flexible. Components can access many different buses through one small internal connector, and you've got a lot of different physical card sizes to play with instead of being tied to either a 'full-height' or 'half-height' card.

Motherboard M2 Slot Screw

The worst thing about M.2 right now is a general scarcity of components. OEMs buying parts directly from manufacturers probably have more choices, end users buying M.2 cards from Newegg or Amazon will find that they have few options, especially compared to the selection of mSATA and mPCIe components. That will change as M.2 goes mainstream and those older connectors begin to fade. Broadwell is a big step forward in that transition.