▷ Slot u.2 what is it and what is it for?

For many years SATA has been the predominant interface in the PC world to connect hard drives. But we have talked little about the Slot U.2 connection that can offer us such good performance and so few devices currently exist.

With the arrival of NAND memory-based SSDs, the bandwidth of the SATA interface has become very limited, which is why we have seen the appearance of alternatives such as M.2 and U.2. In this articles we focus on the U.2 interface. Prepared? Let's start!

What is the U.2 interface that we usually see on current motherboards

The U.2 interface made a major appearance on the motherboards of the latest generations of major manufacturers such as Asus, MSI, Gigabyte, and ASRock. Initially the interface used to be called SFF-8639 and was targeted almost exclusively at the server and enterprise markets. In a move toward greater ease of use, the interface has changed its name to "U.2, " easier to remember with the M.2 interface that has also been proliferating across the market in recent years.

The U.2 form factor was developed by the SSD form factor working group (SFFWG). The specification was released on December 20, 2011 as a mechanism to provide PCI Express connections to SSDs for the enterprise market. The goals included compatibility with existing 2.5 "and 3.5" mechanical hard drives, which can be hot swappable and allow legacy SAS and SATA drives to be mixed using the same connector family.

We recommend you read our article on the best SSDs

The U.2 interface came onto the market with the Gigabyte Intel Broadwell-E processors, about four years ago, so it has been with us for a long time. The U.2 interface shares many features with M.2, such as the fact that it takes advantage of PCI Express lanes to communicate with the processor very quickly, which is ideal for NVMe SSDs. Current Intel and AMD chipsets have high-speed IO lanes that are almost entirely affordable by the motherboard vendor, allowing for greater differentiation between products. These are called HSIO lanes. The Z390 chipset has 26 HSIO lines that can be assigned to GbE, SATA, PCI-e or PCI-e enabled devices such as U.2 and M.2.

The U.2 interface connects directly to the PCI-e lanes on the motherboard, rather than going through the SATA interface. The U.2 pin-out allows the use of 4 PCI-e lanes in total. As such, its maximum theoretical performance in Gen3 is 4 GB / s. The U.2 pin-out looks like the SAS connector, but with many more pins for the lanes. Several of the pins are reserved for the refclock, lanes 0-3, the SMBus, and the dual port. The rest of the pins are used for signaling, power and control, and the other refclock.

U.2 offers performance comparable to M.2 and far superior to SATA Express

On the motherboard, U.2 is a double-deck connector that receives a similar double-deck cable from the SSD. At the other end, a much wider cable connects to 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 drives are inherently faster. SATA Express, meanwhile, communicates to its fullest through 2 PCI-e lines on the motherboard, limiting the interface to 2GB / s on Gen3. SATA Express will become a dead and abandoned standard in no time, as the industry continues to ignore its existence and move entirely to M.2 and U.2 interfaces. SATA Express cannot communicate through 4 PCI-e lines.

For reference, SATA has a maximum theoretical throughput of 600 MB / s, which drops to around 550 MB / s once overhead is taken into account. SATA does not use PCI-e, which is a small advantage for anyone who maximizes the number of lanes of their chipset, but be aware that the storage lanes of the chipset are not the same as the GPU lanes, so even the Multiple GPU configurations cannot conflict with NVMe or PCIe SSD.

M.2, then, is the most comparable to U.2. M.2 is capable of offering the same four-lane performance for storage devices, but it occupies a significantly smaller footprint on the motherboard and limits users solely by physical space. We're interested in U.2 because it can be stacked where the current SATA connectors are, if the PCI-e rails allow it, and theoretically it could run multiple 2.5-inch U.2 SSDs.

This ends our article on what the U.2 slot on the motherboard is and what it is for, we hope you have made everything clear, otherwise you can leave a comment or go to a neutral specialized forum.

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