SATA, SAS and NVMe describe how an SSD talks to the computer; 2.5-inch, M.2 and mSATA describe its shape. A 2.5-inch SATA SSD typically runs at 6Gb/s, while NVMe is the standard for SSDs attached over PCIe. An M.2 card can use either SATA or PCIe, and notches on its edge connector show which.
Interface is not form factor
SNIA says SSDs typically come in three flavors: NVMe, SAS and SATA. Those are interfaces and protocols. The same SSD flavor can come in several physical form factors.
NVM Express says the NVMe specifications define how host software communicates with non-volatile memory across transports such as PCI Express, and that NVMe is the industry standard for SSDs in all form factors, including U.2, M.2 and add-in cards.
So "M.2" alone does not tell you the interface. An M.2 SSD may be SATA or NVMe over PCIe.
2.5-inch drives
SNIA calls the 2.5-inch form factor the most common deployment of an SSD. It is offered with PCIe (with NVMe), SAS or SATA interfaces and is used in desktops, servers and storage systems built around hard disk drives.
SNIA's table lists the 2.5-inch 7 mm SATA SSD as typically 6Gb/s, and the 2.5-inch 15 mm SAS SSD as typically 12Gb/s with dual-port support. A 2.5-inch SSD on a desktop's ordinary drive cables with a 6Gb/s label is a SATA SSD.
M.2 and mSATA cards
SNIA describes M.2, formerly Next Generation Form Factor (NGFF), as a form factor for internally mounted SSDs. It supports PCIe, SATA and USB interfaces, comes in several widths and lengths, and has keying notches on the edge connector to show the interface or PCIe lane configuration.
SATA-IO's comparison gives mSATA as 30 mm wide by 50.95 mm long. M.2 cards are 22 mm wide, in lengths of 30, 42, 60, 80 or 110 mm.
An operating system installer that sees SATA drives but not a new PCIe M.2 SSD is missing an NVMe driver. NVM Express lists driver support for Microsoft and Linux.
Where the exam catches people
Believing every M.2 SSD is NVMe: M.2 supports SATA as well as PCIe, and the edge-connector notches show which.
Believing the driver to load for a PCIe M.2 SSD is a "PCIe" or "M.2" driver: PCIe is the bus and M.2 the shape; the storage protocol driver is NVMe.
Believing a 6Gb/s 2.5-inch SSD is SAS: SNIA lists 2.5-inch SATA SSDs as typically 6Gb/s and SAS as typically 12Gb/s.
Believing mSATA and M.2 are the same card: mSATA is 30 mm wide by 50.95 mm long, while M.2 is 22 mm wide.