U.2, M.2 or E1.L

Which NVMe form factor is right: U.2, M.2 or E1.L?

Carnival of NVMe Cultures

NVMeSSDs from the Western Digital® Ultrastar® DC SN640 are available in three different form factors. We would like to present the individual variants here.

Your benefits Western Digital® NVMe SSDs

  • Easy transition from SATA drives to NVMe SSDs
  • Up to sixfold increase in data throughput
  • Optimal relationship between price and performance
  • Flexible use in different application scenarios possible
U.2, M.2 or E1.L

2.5″ SFF (U.2)

The familiar 2.5-inch form factor is often colloquially equated with U.2. In fact, U.2 originally defined the SFF-8639 hot-swappable PCI Express interface. All manufacturers have been using this SFF enclosure for years for SATA and SAS SSDs as well as for hard disks.

Their external dimensions are always the same, with a width of 69.85 mm and a length of 100.35 mm. They only vary in height: 7 or 15 mm. We use them in desktop PCs, servers and storage systems with LFF and SFF bays.

U.2, M.2 or E1.L


M.2 is a form factor specification for internally installed SSDs. The narrow read-only memories are usually installed parallel to the receiving circuit board without an enclosure. Provided a suitable port is available, they can be installed directly into a mainboard – usually between the PCIe slots – or directly onto a controller. An M2 screw with a length of 3 mm is often used as a fixation against slipping out.

Formerly also called Next Generation Form Factor (NGFF), supports M.2 PCIe (NVMe), SATA and USB interfaces. They are available in widths of 12, 16, 22 or 30 mm. The length varies between 16, 26, 30, 38, 42, 60, 80 or 110 mm. Manufacturers identify their various interface or PCIe lane configurations via notches on the connector edge, the so-called M.2 module keys. (The Ultrastar® DC SN640 from Western Digital® has its notches at pins 59 to 66 and thus only fits in slots with Key ID Type M for NVMe PCIe ×4.)

U.2, M.2 or E1.L


E1.L was adopted as the latest standard in 2017. It is supposed to guarantee particularly energy-efficient storage in terms of terabytes per watt. This slim form factor is primarily used to increase the capacity per drive and rack unit in 1U servers, all-flash arrays and JBODs or JBOFs. These NVMeSSDs require special chassis designed for them, as they are inserted directly from the front.

SSDs with form factor E1.L in the 318.75 mm × 38.4 mm size use eight lanes on the PCIe bus and are specified for a power consumption of up to 40 watts. (The smaller SSD variant E1.S, on the other hand, operates with a maximum of 12 watts on four lanes). In order to increase the ease of maintenance in the data center, the SSDs were designed to be hot-swappable and have integrated cooling fins, which are important for heat dissipation. In addition, E1 SSDs already have built-in LEDs as function indicators.

Have we aroused your interest in our SSDs? – We look forward to talking with you!

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Since 2017, the former technology journalist has been providing new content about Starline products and services in press releases, newsletters, catalogues and on the web. To do this, he had to acquire a few gigabytes of technical data about this new profession for him, in order to familiarise himself with the professional world. Currently he has extended his working environment to include marketing and helps with tradefair preparations, presentation materials and business equipment. After work, he devotes himself entirely to his craft and enjoys working with wood – as an analogue 3D printer, so to speak.