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SSD Guide: SATA vs NVMe, M.2 Sizes and Keys
Learning Center › SSDs
Learning Center
SSD Guide
A solid state drive stores data on NAND flash chips instead of spinning magnetic platters. No moving parts means faster access, better reliability, lower power draw and silent operation. Here is how to tell SSDs apart and pick the right one.
Form factors
Four common shapes.
Traditional
2.5 inch
The classic laptop drive size. Fits laptop drive bays, or desktops with a 3.5" adapter. Usually SATA.
Modern
M.2
A slim stick that plugs straight into the motherboard. Can be SATA or NVMe; sizes and keys below.
Legacy desktop
PCIe add-in card
A full-size card for older desktop motherboards without M.2 slots. Still offers full NVMe speeds.
External
Portable SSD
A small box on a USB or USB-C cable. No tools or installation, and it works with any computer, so it is the safe choice when you are not sure what is inside.
Interfaces
SATA vs NVMe.
| Interface | Best for | Typical max speed |
|---|---|---|
| SATA | Older systems, budget builds, everyday use where raw speed is not critical | ~550 MB/s |
| NVMe (PCIe 3.0) | Modern laptops and desktops, gaming, content creation | ~3,500 MB/s |
| NVMe (PCIe 4.0) | Latest systems, high-end workloads, large file transfers | ~7,000 MB/s |
| NVMe (PCIe 5.0) | Cutting-edge systems, professional workloads | ~14,000 MB/s |
Match the drive to your motherboard. An NVMe drive will not work in a SATA-only slot, and a PCIe 4.0 drive on a PCIe 3.0 motherboard runs at 3.0 speeds. Check which interface your system supports before buying.
M.2 sizes and keys
Check the slot before you buy.
The code on an M.2 drive gives its size: the first two digits are the width and the rest the length, in millimeters. A longer drive never fits a shorter slot.
| Size | Dimensions | Where you will find it |
|---|---|---|
| 2230 | 22 x 30 mm | Ultra-thin laptops, mini PCs, handheld gaming PCs |
| 2242 | 22 x 42 mm | Compact and business laptops, industrial and embedded PCs |
| 2280 | 22 x 80 mm | Most laptops and desktops, by far the most common |
| 22110 | 22 x 110 mm | Servers and workstations, with room for power-loss protection |
The notches in the gold edge are called keys, and they are the quickest clue to the drive type:
| Key | Looks like | Usually means |
|---|---|---|
| M-key | One notch near one edge | PCIe NVMe (x4), nearly all current NVMe SSDs |
| B-key | One notch near the other edge | SATA or PCIe x2; rare on its own today |
| B+M key | Two notches | Almost always M.2 SATA |
The trap: a B+M SATA drive physically fits an M-key slot, but if that slot supports only NVMe the computer will not see it. Fitting is not the same as working; check whether the slot supports SATA, NVMe or both.
Other SSD specs
What else is on the spec sheet.
PCIe lanes and NVMe
PCIe connections are built from lanes; most M.2 NVMe drives use four (x4), and budget drives using two (x2) top out at about half the speed. NVMe is the language the drive speaks over PCIe, designed for flash, so "PCIe SSD" and "NVMe SSD" mean the same thing. PCIe generations work both ways: a Gen5 drive runs in a Gen3 slot at Gen3 speed.
DRAM vs DRAM-less
Many SSDs carry a small DRAM chip as a fast map of where data lives, which keeps speed steady under heavy use. DRAM-less drives cost less; NVMe versions borrow a little of the computer's memory instead (HMB, Host Memory Buffer). Fine for everyday use.
SLC cache: why drives slow down
Most consumer SSDs write first to a fast cache. During a very large copy, once the cache fills, write speed drops, sometimes sharply on QLC and DRAM-less drives. That explains "it started fast, then slowed down".
Portable SSD speed
A portable SSD can only go as fast as its USB link. On a 10 Gbps connection it tops out around 1,000 MB/s, and only in a 10 Gbps port. See the USB guide.
Endurance (TBW). Flash wears with every write, so SSDs are rated in terabytes written. How cell type affects it is in NAND Flash Basics.
Upgrading
Should you upgrade to an SSD?
If you still run a spinning hard drive: yes, without hesitation. An SSD is the single biggest performance upgrade you can make to a computer. Boot times, app launches and file loads all get noticeably faster, and even a budget SATA SSD feels dramatically faster than a hard drive. Setting up a new drive is covered in the FAQ.
SSD or eMMC? eMMC is flash soldered onto the board of embedded devices; an SSD is a drive you can install or replace. See What Is eMMC.
More guides
Keep learning.
NAND Flash Basics
SLC to QLC, endurance, and how to read speed and capacity numbers.
Read the guide →Need SSDs for a build or a program?
Centon Electronics supplies Personal SSDs and OEM SSDs for system builders. Tell us what you are building.
Or call 800-234-9292, Monday to Friday.We’re here to help! Reach out to us with your inquiries, feedback, or support needs. Our team is ready to assist you.
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