NVMe SSD specifications decoded: PCIe generations, form factors and endurance
Sequential read speed is the headline figure and the least relevant one for most people. Here is what actually determines how quick an SSD feels.
SSD marketing has settled on a single number, sequential read speed, which is close to the least useful figure for predicting how a drive will feel in daily use. Understanding the rest of the spec sheet is what separates a good purchase from an expensive one.
Sequential speed is a best case
The advertised "7,400 MB/s read" figure describes reading one large contiguous file under ideal conditions. Real workloads (booting, launching applications, loading game assets) are dominated by many small scattered reads, where drives perform far closer together than their headline numbers suggest.
The practical consequence: the jump from a hard drive to any NVMe SSD is transformative. The jump from a mid-range NVMe drive to a flagship one is, for most people, barely perceptible outside benchmarks.
PCIe generation and lanes
NVMe drives connect over PCIe, and the generation sets the ceiling:
| Interface | Practical ceiling |
|---|---|
| PCIe 3.0 x4 | ~3,500 MB/s |
| PCIe 4.0 x4 | ~7,500 MB/s |
| PCIe 5.0 x4 | ~14,000 MB/s |
Two caveats worth knowing. Generations are backwards compatible: a PCIe 5.0 drive works in a 4.0 slot, at 4.0 speeds. And on many motherboards the M.2 slots share lanes with other components, so populating every slot can reduce a slot's available bandwidth or disable a SATA port. The board manual documents this; it is easy to be caught out by.
PCIe 5.0 drives also run hot enough that a heatsink is effectively mandatory. Many boards include one.
Form factor
M.2 2280 is the standard desktop size (22mm wide, 80mm long) and what almost every desktop board expects. Shorter variants (2230, 2242) exist for laptops and handhelds; the Steam Deck uses 2230. Check what your board or device accepts before buying.
Endurance, and when to care
TBW (terabytes written) is the manufacturer's warranty figure for total writes over the drive's life. A typical 1TB consumer drive is rated somewhere around 600TBW.
To put that in perspective: writing 50GB every single day would take over thirty years to reach it. For ordinary use, including gaming, TBW is not a figure that should influence your decision. It becomes relevant for sustained heavy write workloads: video editing, large database work, continuous logging.
DRAM cache: the spec that is often missing
Better drives include a DRAM cache to hold the mapping table between logical and physical addresses. Cheaper "DRAM-less" drives borrow system memory instead.
Under light use the difference is small. Under sustained load, or when the drive is nearly full, DRAM-less drives slow down noticeably. If a drive is unusually cheap for its capacity and speed, a missing DRAM cache is the most likely explanation.
This is worth more attention than the headline sequential figure.
Buying sensibly
- Capacity first. A larger drive is faster, lasts longer, and avoids the sharp slowdown that comes with a nearly full SSD. Leave 10–20% free.
- Match the interface to your board. A PCIe 5.0 drive in a 4.0 slot is money spent on nothing.
- Prefer DRAM cache if the price difference is small.
- Largely ignore TBW unless you know your workload is write-heavy.
- Treat sequential speed as a tiebreaker, not a primary criterion.
Every SSD on VantaSpec lists Interface, Form Factor, Capacity, Sequential Read, Sequential Write, TBW and Cache, so you can compare the specifications that matter rather than the one on the box.