As one of PC Gamer’s hardware writers and reviewers, I cover a lot of different PC components. But there is one part in particular that annoys me every time I use one. I’m talking about M.2 SSDs. In fact, I hate them. They have so many unnecessary disadvantages. I agree the form factor is great for laptops, but for a desktop PC? No.
What’s really frustrating is that there’s an off-the-shelf alternative with all the benefits of M.2, and essentially none of the drawbacks. It’s called U.2 (with U.3 waiting in the wings). Unfortunately, despite fleeting additions on some boards a few generations ago, U.2 never caught on in the consumer space. And I want it back.
When the first SSDs hit the market, it became clear that the outdated SATA and mSATA interfaces were not enough to handle the increasing speeds of these flashy new flash drives.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 not a connector, it is a specification or protocol. NVMe devices are available in different form factors with different connections. These include PCI Express expansion 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 appeared on some high-end consumer motherboards a few years ago, but it has always been more of an enterprise-oriented solution. It lives on and many workstation motherboards still include U.2 ports.
The height of M.2
For some bono-headed reason, someone decided that connecting an SSD directly to the motherboard was the best solution. M.2 quickly became the most commonly used connection, and to this day almost every performance-based consumer SSD is an NVMe M.2 drive in the 2280 form factor.
So why do I think M.2 SSDs are bad? Where do I begin? A typical 2280 size drive is too small, both physically and in capacity. They get hot and are prone to throttling. They often sit right next to (if not directly underneath) a heat dissipation graphics card. Coincidentally, this week I reviewed a Teamgroup Siren Duo360 AIO cooler that also comes with an integrated SSD water block. Unfortunately, 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 especially PCIe 5.0 M.2 slots add complexity to motherboards, making them more expensive. They take up a lot of PCB space. They are difficult and fiddly to install, sometimes requiring removing the GPU and removing half a dozen tiny screws – which I too often drop and lose in the seventh circle of hell. Then you have to put everything back together and hope that a weak, thin, or crumbling thermal pad lines up and the drive actually fits securely into the M.2 slot. There are a handful of reasons to start with.
Why U.2 rocks
U.2 drives eliminate all these problems while retaining all 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 almost every way. This is why:
A U.2 drive can be isolated from other heat-generating components, especially the graphics card. A physically separated drive is easier to cool. Most PC cases have 2.5-inch or 3.5-inch drive bays, and placing three or four U.2 drives in a space cooled by a 120mm intake fan will keep them cool at all times . This prevents them from throttling, leading to a longer lifespan and therefore keeping your data more secure. This last point is often overlooked.
A drive with a 2.5-inch form factor can easily contain a significant heat sink, either internal or part of the drive’s casing (as seen in the example above). Furthermore, SSD manufacturers are not limited by the M.2 2280 form factor PCB. That means more PCB space is available for more dies and larger capacities, or physically larger controllers with improved heat dissipation properties. They could even use cheaper production nodes.
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And of course, getting rid of some M.2 slots frees up space on the motherboard PCB and eliminates the need to cover half the motherboard with sheets of metal to keep the drives cool.
It’s easier to route signals from stacked connectors rather than running electrically sensitive traces in all directions on 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 can cost over €500?
A lesser known but important fact is that U.2 drives use 12V power, while M.2 only uses 3.3V. There is momentum in the industry to move PCs to 12V-only designs. Intel released the ATX12VO standard in 2019, but it has not caught on. A PC with only 12V is more efficient, simpler in design and hopefully cheaper to produce. There is one more point in favor of U.2.
Do I care about seeing an inch of cable sticking out of the side of my motherboard before it disappears through a hole and out of sight? Not. A. Bit.
A 2.5-inch U.2 SSD is easy to install and hot-swappable. It can be installed in any of a million cases with tool-less 2.5-inch drive bays. Plug in the cable and power connector and you’re ready to go. Perhaps some small systems would be at a disadvantage, but a 2.5-inch drive bay or three doesn’t require a monster-sized case. Only the smallest NUC-type systems would be disadvantaged, and they are more likely to use custom motherboards and still be able to include M.2 slots.
Are there any disadvantages to using U.2 over M.2? Well, you need a cable to connect them. Some would say that M.2 drives are a more elegant solution. No cables means a cleaner construction. But do I care about seeing an inch of cable sticking out of the side of my motherboard before it disappears through a hole and out of sight? Not. A. 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 are small, clunky, hot, harder to install, add cost and complexity to motherboards, and have limited capacity. U.2 addresses all of these weaknesses, but requires slightly more cabinet space and cable usage. Big problem. These are compromises that I am more than willing to accept.
U.2 drives clearly have the edge. Give me the option and I will follow. But no matter what happens, with or without you, the insatiable desire for fast flash storage won’t go away. I just hope the future isn’t all lemon M.2 drives. If U.2 makes a comeback, it will be a great day.