Buying an SSD used to be simple: pick a capacity. Now the listings bristle with SATA, NVMe, M.2, “Gen 4”, DRAM-less, and TBW, and two drives at the same price and size can differ in speed by a factor of ten. Here’s what each term means and which ones should actually steer your purchase.

SATA vs NVMe is the speed fork in the road

The biggest divide is the interface the drive talks over. SATA is the older path, capped at roughly 550 megabytes per second — still a massive upgrade over a spinning hard drive, and plenty for everyday computing. NVMe drives run over PCIe lanes instead and leave SATA far behind, reaching several thousand megabytes per second. If your computer supports NVMe, it’s the better buy for anything performance-sensitive.

M.2 is a shape, not a speed

M.2 describes the physical stick-of-gum form factor, and this trips people up constantly: an M.2 drive can be either SATA or NVMe. The slot looks nearly identical, but the drive inside runs at very different speeds. Before buying, check that your motherboard’s M.2 slot supports NVMe, and check whether the drive you’re eyeing is the SATA or NVMe variant. A common size marking, “2280”, just means 22 mm wide by 80 mm long.

PCIe generations set the NVMe ceiling

Among NVMe drives, the PCIe generation sets the top speed. Gen 3 tops out around 3,500 megabytes per second, Gen 4 roughly doubles that, and Gen 5 doubles it again — at higher cost and with more heat to manage. The important caveat: the drive and the slot both have to support the higher generation, and they run at the lower of the two. A Gen 5 drive in a Gen 3 slot performs like Gen 3.

Endurance: what TBW tells you

TBW — terabytes written — is the manufacturer’s rating for how much data you can write to the drive over its warranty life. The numbers are large; for typical use you’re unlikely to reach them before you replace the machine. TBW matters mainly for heavy workloads like video editing or constant large transfers. For most people it’s a reassurance figure, not a deciding one.

The quiet spec: DRAM

Some budget SSDs are “DRAM-less”, omitting a small cache chip that helps the drive track where data lives. They look fine in short benchmarks but can slow down under sustained load. If a deal looks unusually cheap for its speed rating, a missing DRAM cache is often why. For a boot drive or light use it’s a fair trade; for a busy working drive, a model with DRAM holds up better.

Matching the drive to the job

For a general laptop or a big media library, a good SATA or Gen 3 NVMe drive is ample and easy on the wallet. For a fast desktop, gaming rig, or creative workstation, a Gen 4 NVMe drive with DRAM hits the sweet spot of speed and value. Gen 5 is for specialists who move enormous files and can handle the heat. As always, buy for the work you actually do, not the biggest number on the shelf.