The standard SATA 2.5″ SSD
In most laptops you’ll find a 2.5″ HDD or SSD bay to insert a 2.5″ SATA SSD or HDD. The 2.5″ indicates the form factor. This is a standardised form in width and length. The height doesn’t matter. You can easily insert a 7mm SSD in a 9.5mm bay. This should be no problem. If you want to upgrade your laptop with a SSD, you will likely need a 2.5″ SATA SSD. Popular models are the Samsung Evo, Kingstond SSDNow, and Crucial BX100. This 2.5″ SSD support maximum SATA transfer speed of SATA-600 (6 Gbit/s, 600 MB/s, or SATA3). This is more than fast enough for most computer users. In the HDD Caddy you can fit a 2.5″ size SSD or HDD with SATA connection. The HDD Caddy support SATA-600 speed.
The mSATA SSD, (mini SATA SSD)
The mSATA SSD are smaller than the 2.5″ SSD. The size of the mSATA SSD is based on Wifi cards. This size doesn’t fit in most laptop HDD bays also not in the HDDCaddy (only with a 2.5″ adapter case). The advantage of this mSATA size is that it is fairly small helping to reduce the bulkiness of a laptop. The mSATA SSD is sometimes installed in thin laptops or ultrabooks. Performance wise there is no advantage. In most test the 2.5″ SATA controller performs better than the mSATA. Max. speed of the mSATA is also SATA-600. Unfortunately mSATA is limited in size capacity due to its format it cannot hold more storage chips.
M.2 NGFF SSD: SATA & PCI-E
Nowadays there is something new on the market, which is called M.2 NGFF SSD. Similar as the mSATA it is fairly compact compared to the standard 2.5″ SATA format. You will also find these SSD types installed in high-performance ultrabooks. The M.2 NGFF is an improvement on the mSATA format. It can now hold more capacity on the same surface. For the M.2 NGFF SSD there are actually two types: SATA and PCI-E. SATA as the 2.5″ SATA and mSATA. It supports maximum transferspeed of SATA-600. The PCI-E is a lot faster, it can four times faster than SATA. The PCI-e 3.0 x4 can reach speeds of 2.500/1.500MB/s. However to utilize PCI-E potential you need to have a PCI-E slot. Currently you can find this slot only in some high performance ultrabooks and PC motherboards. However standardization is not really great. There are different sizes in length. The M.2 SSD is available from 42mm to 80mm size (80mm is most used). Then you have the different in compatibility. Currently there are B-Key slots that are only compatible with SATA and PCIe x2 SSD’s and there are M-key slots that are only compatible with PCIe x4 SSDs.