What Is An SSD (Solid-State Drive)? - TechTarget

SSD form factors

SSD manufacturers offer diverse form factors. The most common form factor is a 2.5-inch SSD that is available in multiple heights and supports SAS, SATA and NVMe protocols.

The Solid State Storage Initiative, a project of the Storage Networking Industry Association, identified the following three major SSD form factors:

1. SSDs that come in traditional HDD form factors and fit into the same SAS and SATA slots in a server.
2. Solid-state cards that use standard add-in card form factors, such as those with a PCIe serial port card. A PCIe-connected SSD does not require network host bus adapters to relay commands, which speeds the performance of storage. These devices include the U.2 SSDs that are generally considered the eventual replacement for drives used in thin laptops.
3. Solid-state modules that reside in a DIMM or small outline dual in-line memory module. They may use a standard HDD interface such as SATA. These devices are known as non-volatile DIMM (NVDIMM) cards.

Two types of RAM are used in a computer system: DRAM, which loses data when power is lost, and static RAM. NVDIMMs provide the persistent storage a computer needs to recover data. They place flash close to the motherboard, but operations are carried out in DRAM. The flash component fits into a memory bus for backup on high-performance storage.

Both SSDs and RAM incorporate solid-state chips, but the two memory types function differently within a computer system.

Two newer form factors worth noting are M.2 and U.2 SSDs. An M.2 SSD varies in length -- typically from 42 millimeters (mm) to 110 mm -- and attaches directly to a motherboard. It communicates via NVMe or SATA. The small size of an M.2 limits the surface area for heat dissipation which, over time, will reduce its performance and stability. In enterprise storage, M.2 SSDs often are used as a boot device. In consumer devices, such as notebook computers, an M.2 SSD provides capacity expansion.

A U.2 SSD describes a 2.5-inch PCIe SSD. These small form-factor devices were formerly known as SFF-8639. The U.2 interface enables high-speed NVMe-based PCIe SSDs to be inserted in a computer's circuit board, without the need to power down the server and storage.