SSDs and HDDs – NVMe vs SATA, M.2 and PCIe generations
The difference between SATA and NVMe drives, what M.2 means, PCIe 4.0 and 5.0, the theoretical maximums of each interface, and why an M.2 slot does not automatically mean NVMe.
The short version
- M.2 is a form factor, not a speed. An M.2 drive can be SATA (interface up to 6 Gb/s) or NVMe over PCIe.
- An NVMe drive in a PCIe 4.0 ×4 slot has a theoretical interface bandwidth of about 7.9 GB/s in one direction; PCIe 5.0 ×4 roughly double that.
- Hard disk drives (HDDs) are cheaper per terabyte and suit archiving. For the system and programs, an SSD is much faster.
Three terms that get mixed up
The form factor (2.5″, 3.5″, M.2) tells you how big the drive is and what connector it has. The interface (SATA, PCIe) tells you how the drive connects to the computer. The protocol (AHCI, NVMe) is the language the computer and the drive use to talk to each other.
The most common mistake: “M.2 = NVMe”. It is not. SATA drives are also made for M.2 slots, and some M.2 slots support only one of the two types. If you put an NVMe drive into a slot that only supports SATA, the drive will not show up.
Theoretical interface maximums
| Interface | Speed per specification | Theoretical bandwidth (one direction) |
|---|---|---|
| SATA III (SATA 6Gb/s) | 6 Gb/s | ≈ 600 MB/s |
| PCIe 3.0 ×4 | 8 GT/s per lane | ≈ 3.9 GB/s |
| PCIe 4.0 ×4 | 16 GT/s per lane | ≈ 7.9 GB/s |
| PCIe 5.0 ×4 | 32 GT/s per lane | ≈ 15.8 GB/s |
How we calculated it: PCIe 3.0 to 5.0 use 128b/130b encoding, so of every 130 bits transferred, 128 are payload. PCIe 4.0 ×4 = 16 GT/s × 4 lanes × 128/130 ÷ 8 ≈ 7.9 GB/s. For PCIe 5.0, PCI-SIG quotes “up to 128 GB/s at ×16”, which is the total of both directions – for ×4 and one direction that works out at roughly 16 GB/s. SATA 6 Gb/s uses 8b/10b encoding, hence the ceiling of around 600 MB/s; in its revision 3.0 document, SATA-IO mentions drives exceeding 580 MB/s.
These are interface ceilings. A drive’s real speed depends on its controller, its flash chips, file sizes and temperature. Drive makers quote sequential speeds that you will not reach in everyday work with lots of small files.
When a faster drive makes sense
You will notice the difference between an HDD and any SSD immediately when the system starts and programs open – an SSD has no mechanical heads that have to seek the data. The difference between a SATA SSD and NVMe is noticeable when copying large files or working with video. The difference between PCIe 4.0 and 5.0 is something you will mostly not notice in everyday office work.
HDDs still have their place
Hard disk drives suit backups and archives, where capacity is what counts. We no longer recommend them for laptops or as a system drive – they are slower and sensitive to knocks. If you need to connect an HDD externally, see the guide to external drives and enclosures.
Lane sharing
On many boards, some M.2 slots share lanes with SATA ports or with another slot. When you populate an M.2 slot, two SATA ports might be disabled, for example. You will find these limitations in the board manual, in a table along the lines of “M.2 / SATA sharing”.
Before you finish
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Notes and sources
- SATA-IO: Fast Just Got Faster: SATA 6Gb/s (white paper)
- PCI-SIG (press release): PCI Express 5.0 – 32 GT/s, up to 128 GB/s at ×16
- PCI-SIG: PCI Express 6.0 Specification
- AMD: AMD Socket AM5 Chipset – chipsets, PCIe lanes, USB
We opened every link above and compared the figures on 12 October 2026. The pages belong to their publishers and can change after that date.
Something here does not match the source? dielna@petme.sk. How corrections work is on the How we work page.