As one of PC Gamer’s hardware writers and reviewers, I cover many different PC parts. But there is one part that bothers me especially every time I use it. I’m talking about M.2 SSDs. I actually hate them. It has so many unnecessary disadvantages. I’ll admit the form factor is well suited to laptops, but for a desktop? No.
What’s really frustrating is that there is a readily available alternative that has all the advantages of M.2, with essentially no disadvantages. This is called U.2 (while U.3 waits in the wings). Unfortunately, despite making a temporary appearance on some motherboards a few generations ago, U.2 never caught on in the consumer space. And I want it back.
When the first SSDs were introduced, it became clear that aging SATA and mSATA interfaces were inadequate to handle the increasing speeds of these flashy new flash drives. A new standard was needed. NVM Express was developed specifically for non-volatile memory (NVM), but NVMe is a specification or protocol, not a connector. NVMe devices come in various form factors with different connections. These include PCI Express add-in cards or have SATA Express, M.2 or U.2 connectors.
SATA Express was never caught on. Some high-end Intel Z97 and X99 motherboards came with SATA Express ports, but I didn’t test any of them and all support disappeared soon after.
My champion, U.2, made brief appearances on some high-end consumer motherboards a few years ago, but has always been more of an enterprise-focused solution. It still exists, and many workstation motherboards still have U.2 ports.
Height of M.2
For some logical reason someone decided that connecting the SSD directly to the motherboard was the best way to go. M.2 has quickly become the most widely adopted connection, and to date nearly every performance consumer SSD is a 2280 form factor NVMe M.2 drive.
So why do I think M.2 SSDs suck? Where do I start? A typical 2280 size drive is very small both physically and in capacity. They run hot and are prone to suffocation. They are usually located right next to (though not directly below) the graphics card with heat dump. Coincidentally, this week I reviewed the Teamgroup Siren Duo360 AIO cooler, which comes with an integrated SSD water block. Unfortunately, it highlights a growing problem with SSDs. It’s a shame that PCIe 5.0 SSDs need large coolers mounted on the motherboard, let alone water cooling.
PCIe 4.0 and especially PCIe 5.0 M.2 slots add complexity to motherboards, making them more expensive. They take up a lot of PCB space. Installation is difficult and fiddly, sometimes requiring removing the GPU and removing half a dozen small screws; Most of the time I drop these and lose them to the seventh circle of safe hell. You then have to put it all back together and hope that the weak, flimsy or crumbling thermal pad lines up and the drive is actually securely inserted into the M.2 slot. There are a few reasons to start.
Why is U.2 great?
U.2 disks eliminate all these problems while maintaining all the advantages. A U.2 drive can be considered a modernized 2.5-inch SATA drive that supports NVMe PCIe connectivity. In my opinion, they are superior to M.2 drives in basically every way. Here’s why:
The U.2 driver can be isolated from other heat-generating components, especially the graphics card. A physically separate drive is easier to cool. Most computer cases have 2.5-inch or 3.5-inch drive bays, and placing three or four U.2 drives in an area cooled by a 120mm intake fan will keep them cool at all times. This prevents them from shrinking, ensuring a longer lifespan and therefore keeping your data safer. The second point can often be overlooked.
A 2.5-inch form factor drive can easily include a fairly large heat sink either internally or by forming part of the drive enclosure (as seen in the example above). Moreover, SSD manufacturers are not limited to M.2 2280 form factor PCB. This means more PCB space is available for more dies and physically larger controllers with larger capacities or improved heat dissipation properties. They can even use cheaper production nodes.
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And of course, getting rid of a row of M.2 slots frees up motherboard PCB space and eliminates the need to cover half the motherboard with sheets of metal to keep drives cool.
It’s easier to route signals from stacked connectors rather than having electrically sensitive traces all over the motherboard. I’m sure a motherboard with one M.2 slot and four stacked U.2 ports would be cheaper to produce. Is it any wonder that a high-end motherboard costs more than $500?
A less known but important fact is that U.2 drives use 12V power, while M.2 only uses 3.3V. There is some industry momentum towards shifting PCs to 12V-only designs. Intel released the ATX12VO standard in 2019 but it has not yet caught on. A 12V-only computer is more efficient, simpler in design, and hopefully cheaper to manufacture. There is another point in favor of U.2.
Do I care about seeing an inch of cable coming out the side of my motherboard before it disappears through a hole? Negative. One. A little.
The 2.5-inch U.2 SSD is easy to install and hot-swappable. It can be installed in one of the million chassis with tool-free 2.5-inch drive bays. Plug in the cable and power connector and you’re good to go. Maybe some smaller systems would be at a disadvantage, but it’s not like a 2.5-inch drive bay or three would require a monster-sized case. Only the smallest NUC-type systems will be at a disadvantage, and they are more likely to use dedicated motherboards and may still include M.2 slots.
Are there any disadvantages to using U.2 over M.2? You need to use a cable to connect them. Some might say M.2 drives are a more elegant solution. No cables means a cleaner build. But do I care about seeing an inch of cable coming out the side of my motherboard before it disappears through a hole? Negative. One. A little. Someone can make an RGB U.2 cable.
Oh, I can’t believe I went there.
I’m sorry, but I can’t fall in love with M.2 SSDs. They are small, cumbersome, hot, harder to install, add cost and complexity to motherboards, and have limited capacity. U.2 addresses all of these weaknesses at the expense of requiring slightly more chassis space and cable usage. Something important. These are trades I’m more than willing to accept.
U.2 drivers clearly have the upper hand. Give me the option and I will follow. But no matter what happens, whether you are or not, the insatiable desire for fast flash storage will not go away. I hope the future isn’t all about lemon M.2 drives. It will be a good day if U.2 makes a comeback.