M.2 vs PCIe for ssd

The M.2 3.0 x 4 ssd's and the PCIe 3.0 x 4 ssd's each use four PCIe 3.0 channels to transmit and receive data. Technically they are both PCIe 3.0 x 4 drives.

The M.2 ssd's are tiny drives that are about the size of a stick of chewing gum. Normally they are inserted into a small M.2 slot on the motherboard. No PCIe adapter cards or special cables are required. The M.2 ssd's are replacements for the old mSATA ssd's used in mobile pc's. Because the new drives were replacing mSATA drives, the Name M.2 was used instead of PCIe even though the M.2 drives use PCIe channels.

Then a curious thing happened. The M.2 drives were designed for use in mobile pc's where available space is limited. Motherboard manfuacturers decided to add M.2 slots in desktop systems as a cost saving measure. They could make one ssd that could fit both desktop pc's and mobile pc's.

Next came more confusion. If an M.2 ssd was mounted on an PCIe adapter card that was inserted into a PCIe 3.0 x 16 slot on a motherboard, it was called a PCIe ssd.

The Plextor M6e ssd is a perfect example. Plextor offers the M6e as an M.2 and a PCIe ssd. The PCIe version is nothing more than the M.2 version mounted on a PCIe adapter card.

The Samsung 950 Pro is another example. Samsung only offers the 950 Pro as an M.2 drive. Some users have installed the 950 Pro on PCIe adapter cards which results in the 950 Pro being referred to as PCIe drive.

The general rule of thumb is that M.2 ssd's and PCIe ssd's are both PCIe drives by virtue of the fact they both use PCIe channels to transmit and receive data. The differences are how they are connected to a motherboard and their overall physical size.

The Intel 750 model usually referred to as the AIC version is another variation. The ssd is mounted inside a standard 2.5 inch ssd enclosure which can be installed in a drive bay. The ssd is connected to an M.2 slot on the motherboard with a special cable. Currently the cable is included at no extra cost. The AIC model was actually designed for use in business enterprise data centers rather than consumer use.