Internal storage type

Internal storage is available in a variety of shapes, sizes and speeds. Which type is needed depends on the available storage expansion slots and ports on a PC board or in a system.
Common internal storage types:

Solid State Drive (SSD)
mSATA SSD
M.2 SSD

Solid State Drive

Pros: wide available storage type, installation may be easy due to easy accessable bays.
Cons: relativy large in size, not the fastest storage type.

An SSD drive or Solid State Drive is connected to a system with the SATA data and power connector and is available in two form factors:

2.5-inch SATA drive
1.8-inch SATA drive

2.5-inch SATA drive

The 2.5 inch drive (or SATA SSD) requires a disk drive bay or backet to be installed in a system. Dimensions are roughly 100 x 70 mm.

1.8-inch SATA drive

The 1.8 inch drive (or half-slim SATA SSD) requires a disk drive bay or backet to be installed in a system. Dimension are roughly 54 x 39 mm.

mSATA SSD

Pros: available in small sizes.
Cons: not the fastest storage type.

An mSATA drive or Mini SATA SSD is available in two form factors:

mSATA full size
mSATA half size

mSATA (full size)

This mSATA SSD requires a full size Mini PCI Express (mPCIe) slot on a PC board with SATA functionality. Dimensions are roughly 50.8 x 29.8 mm.

mSATA (half size)

This mSATA SSD requires a half size Mini PCI Express (mPCIe) slot on a PC board with SATA functionality. Dimensions are roughly 26.8 x 29.8 mm.

M.2 SSD

Pros: available in small sizes and high speeds available.
Cons: due to a wide varity in specifications finding the right M.2 SSD may take some effort.

An M.2 SSD drive, introduced as Next Gen Form Factor (NGFF), has evolved from mSATA and is designed to be a thin and light storage solution. The M.2 SSD makes use of the PCIe bus, which makes speeds of 4 GB/s possible when using NVMe protocol.

Form factor

The M.2 module is available in multiple form factors. The form factor specifies the length, width and height of the module, if the drive is single- or double-sided and the connector keys, which determines the device type and the available interfaces. E.g. M.2 2280-D2-B-M indicates an 22 x 80 mm M.2 module with components on the top and bottom side which fits in a B or M connector.

Length & width

The form factor type designates the X and Y dimension (width and length) of the module. This specification is given in the Form Factor specification as e.g. 2280 = 22 mm x 80 mm. Common M.2 form factors lengths for storage are:

M.2 42mm
M.2 80mm

M.2 42mm

This M.2 module requires a M.2 slot with 42 mm length option on a PC board. Dimensions may vary in width (most common is 22 mm), with a maximum length of 42 mm.

M.2 80mm

This M.2 module requires a M.2 slot with 80 mm length option on a PC board. Dimensions may vary in width, (most common is 22 mm) with a maximum length of 80 mm.

Top and bottom side

Components on an M.2 module can be mounted on the top or also on the bottom side. This determines the height of the module. The height is indicated by a designator that consists of a letter (single- or double-sided) and figure.

Designator	Top side (mm)	Bottom side (mm)
S1	1.2
S2	1.35
S3	1.5
D1	1.2	1.35
D2	1.35	1.35
D3	1.5	1.35

Connector keys

An M.2 module supports multiple device types. Next to storage, M.2 provides great flexibility for system peripherals such as expansion modules for wireless or cellular connections, expansion modules for interfaces, or even processing expansion modules. Which interfaces are available is determined by the keying. The keys in a module determines the slot it fits on a board or in a system.

Key	Interface
A	2x PCIe x1 / USB 2.0 / I2C / DP x4
B	PCIe x2/SATA/USB 2.0/USB 3.0/HSIC/SSIC/Audio/UIM/I2C
E	2x PCIe x1 / USB 2.0 / I2C / SDIO / UART / PCM
M	PCIe x4 / SATA