You know M.2 SSDs suck, right?

As one of PC Gamer's hardware writers and reviewers, I handle a lot of different PC parts. But there's one part in particular that manages to irk me every time I use one. I'm referring to M.2 SSDs. In fact, I hate them. They have so many unnecessary drawbacks. I'll admit the form factor is well suited to laptops, but for a desktop PC? Nope.

What's really frustrating is that there's a ready-made alternative with all of M.2's advantages, and essentially none of its drawbacks. It's called U.2 (With U.3 waiting in the wings). Sadly, despite fleeting inclusions on some boards a couple of generations ago, U.2 never caught on in the consumer space. And I want it back.

When the first SSDs launched, it became apparent that the aging SATA and mSATA interfaces were insufficient to handle the increasing speeds of these flashy new flash drives. A new standard was required. NVM Express was developed specifically for non-volatile memory (NVM), but NVMe isn't a connector, it's a specification or protocol. NVMe devices come in a variety of form factors with different connections. These include PCI Express add-in cards or they have SATA Express, M.2, or U.2 connectors. 

SATA Express never caught on. Some high-end Intel Z97 and X99 motherboards came with SATA Express ports but I never tested one and all support disappeared after a short time. 

U.2—my champion—briefly made appearances on some high-end consumer motherboards a few years ago, but it's always been more of an enterprise-oriented solution. It lives on, and many workstation motherboards still include U.2 ports. 

M.2's elevation

For some bono-headed reason, somebody decided that attaching an SSD directly to the motherboard was the best path forward. M.2 rapidly became the most widely adopted connection and to this day, almost every performance-based consumer SSD is a 2280 form factor NVMe M.2 drive.

So, why do I think M.2 SSDs suck? Where do I begin? A typical 2280 size drive is too small, both physically and capacity wise. They run hot and are prone to throttling. They often sit right next to (if not directly underneath) a heat dumping graphics card. Coincidentally, this week I reviewed a Teamgroup Siren Duo360 AIO cooler which also comes with an integrated SSD water block. Sadly, it highlights a growing problem with SSDs. The fact that PCIe 5.0 SSDs require chunky motherboard mounted heatsinks, let alone water cooling, is a pretty sad state of affairs.

PCIe 4.0 and particularly PCIe 5.0 M.2 slots add complexity to motherboards making them more expensive. They take up a lot of PCB space. They're difficult and fiddly to install, sometimes requiring the removal of the GPU and the removal of a half dozen tiny screws—which I too often drop and lose to the seventh circle of case hell. Then you've got to put it all back together, and hope that a weak, flimsy, or crumbling thermal pad aligns and the drive is actually securely fitted in the M.2 slot. There's a handful of reasons to start with.

Why U.2 rocks

U.2 drives eliminate all of these problems while keeping all of the benefits. A U.2 drive can more or less be considered a modernized 2.5-inch SATA drive with support for an NVMe PCIe connection. In my opinion, they are superior to M.2 drives in basically every way. Here’s why:

A U.2 drive can be isolated from other heat generating components, particularly the graphics card. A physically separate drive is easier to cool. Most PC cases retain 2.5-inch or 3.5-inch drive bays, and plonking three or four U.2 drives into a space cooled by a 120mm intake fan will keep them cool at all times. That'll prevent them from throttling, leading to a longer life and hence keep your data safer. The latter point can often be overlooked.

A 2.5-inch form factor drive can easily incorporate a sizable heatsink, either internally or form part of the drive's housing (as seen in example above). On top of that, SSD manufacturers aren't restricted by the M.2 2280 form factor PCB. That means there's more PCB space available for more dies and larger capacities, or physically larger controllers with improved heat dissipation properties. They could even use cheaper manufacturing nodes.

And of course, getting rid of a bunch of M.2 slots frees up motherboard PCB space and gets rid of the need to cover half the motherboard with slabs of metal to keep the drives cool. 

It's easier to route signals from stacked connectors rather than have electrically sensitive traces running every which way across the motherboard. I'm certain that a motherboard with one M.2 slot and four stacked U.2 ports would be cheaper to manufacture. Is it any wonder that a high-end motherboard can cost well over $500?

A lesser known but important fact is that U.2 drives use 12V power, whereas M.2 uses 3.3V only. There's some industry momentum towards shifting PCs to 12V only designs. Intel released the ATX12VO standard in 2019 but it hasn't caught on. A 12V only PC is more efficient, simpler in design, and hopefully cheaper to manufacture. There's another point in U.2's favor.

A 2.5-inch U.2 SSD is easy to install and it's hot swappable. It can be installed in one of the million cases with toolless 2.5-inch drive bays. Plug the cable and power connector in and you’re good to go. Perhaps some tiny systems would be disadvantaged, but it's not like a 2.5-inch drive bay or three requires a monster sized case. Only the smallest NUC type systems would be disadvantaged, and they’re more likely to use custom motherboards and could still include M.2 slots anyway.

Are there drawbacks to using U.2 over M.2? Well, you need to use a cable to connect them. Some would say that M.2 drives are a more elegant solution. No cables means a cleaner build. But do I care about seeing an inch of cable sticking out the side of my motherboard before it disappears through a hole and out of sight? Not. One. Bit. Someone could make an RGB U.2 cable. 

Oh, I can’t believe I went there.

Sorry, but I can't fall in love with M.2 SSDs. They're small, fiddly, hot, more difficult to install, add cost and complexity to motherboards and they're capacity limited. U.2 addresses all of these weaknesses at the cost of requiring a little more case space and the use of cables. Big deal. Those are trade-offs I'm more than willing to accept.

U.2 drives clearly have the edge. Give me the option and I will follow. But, whatever happens, with or without you, the insatiable desire for fast flash storage isn't going to go away. I just hope that the future isn't all lemon M.2 drives. If U.2 makes a comeback, it'll be a beautiful day.