M.2 is a physical form factor for SSDs — a small rectangular module that slots into a dedicated connector on the motherboard. The benefits: compact, no cables needed, and fast. The confusion: M.2 slots support different interfaces (PCIe vs SATA), different generations of PCIe, and different physical sizes.
The Form Factor Numbers: 2280, 2242, 2260
These numbers describe the physical dimensions in millimetres. 2280 means 22mm wide and 80mm long — the standard M.2 size used in most desktop motherboards. 2242 means 22mm × 42mm — smaller, found in some laptops and specialty builds. Most desktop motherboards support 2280 and may also support 2242 with an adapter standoff.
PCIe NVMe vs SATA M.2: The Interface Matters
An M.2 slot can run two different interfaces: PCIe NVMe or SATA. PCIe NVMe (3.0 or 4.0 or 5.0) is dramatically faster — sequential reads of 3,500 to 14,000 MB/s. SATA M.2 is limited to SATA speeds (around 550 MB/s), regardless of the physical connector type.
Check your motherboard specification: not all M.2 slots support PCIe NVMe. Some budget motherboards have M.2 slots that only support SATA speeds. Putting a fast PCIe NVMe SSD into a SATA-only M.2 slot will result in the SSD running at SATA speeds.
PCIe Generation
PCIe 4.0 M.2 SSDs require a PCIe 4.0 M.2 slot to achieve their rated speeds. Running a PCIe 4.0 SSD in a PCIe 3.0 slot works (they are compatible), but the SSD will operate at PCIe 3.0 speeds (~3,500 MB/s). Same applies to PCIe 5.0 SSDs in PCIe 4.0 slots.
The practical implication: match your SSD generation to your motherboard's supported M.2 generation. Buying a PCIe 5.0 SSD for a motherboard that only supports PCIe 4.0 slots is wasted money.