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Difficulty: MediumStorage Devices and Interfaces

A technician is installing a replacement M.2 solid-state drive into a workstation motherboard. The motherboard documentation states that the primary M.2 slot is M-keyed and routed exclusively to four PCIe 4.0 lanes without SATA controller fallback. The technician attempts to install an M.2 SSD that communicates via the SATA protocol and features a B+M keying configuration. Which of the following outcomes is most likely to occur?

  1. The drive will physically fit into the M.2 slot, but the operating system will not detect it because the slot lacks SATA bus routing.Answer
  2. B
    The drive will be physically blocked from insertion because M-keyed motherboard slots reject B+M keyed drive edge connectors.
  3. C
    The drive will operate normally and automatically upgrade its bus communications to utilize PCIe 4.0 x4 throughput capabilities.
  4. D
    The drive will function properly, but its operational transfer bandwidth will be reduced to PCIe 3.0 x2 speed limits.

Answer

The drive will physically fit into the M.2 slot, but the operating system will not detect it because the slot lacks SATA bus routing.
B+M key edge connectors are physically designed to fit both B-key and M-key slots. However, because the motherboard slot is wired strictly for PCIe lanes and does not connect to a SATA controller, the system cannot establish logical communication with a SATA protocol drive, leaving it undetected.

Step-by-Step Solution

1
Analyze physical keying compatibility between the drive and slot.
B+M keyed M.2 drives have cutout notches for pins 12–19 (B-key) and pins 59–66 (M-key), allowing them to physically seat into an M-keyed motherboard slot.
Physical compatibility is determined by edge connector pin alignment.
2
Analyze logical protocol and motherboard bus routing compatibility.
The target motherboard slot provides only PCIe bus connectivity, but the SSD relies on a SATA storage controller protocol.
M.2 slots can support PCIe, SATA, or both depending on motherboard chipset routing.
3
Determine the functional outcome of inserting a SATA drive into a PCIe-only M.2 slot.
Without a SATA controller connected to the M.2 slot, the system hardware cannot communicate with the drive's SATA controller, leaving it undetected in BIOS/UEFI and OS.
Physical fit does not guarantee protocol compatibility.

Key Concept

M.2 Physical Keying vs. Storage Protocol Compatibility
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Topics

Storage Devices and Interfaces

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