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Difficulty: Very hardStorage Devices and Interfaces

A system administrator is installing drives into a specialized workstation motherboard. The motherboard documentation specifies that the primary slot (M2_1) is M-key only and connected exclusively to four PCIe 4.0 lanes without SATA controller routing. The secondary slot (M2_2) is B-key only and connected to two PCIe 3.0 lanes and a SATA III controller. The administrator attempts to install a B&M-keyed M.2 SATA SSD into slot M2_1 and a standard M-keyed M.2 PCIe 4.0 NVMe SSD into slot M2_2. Which of the following describes the physical compatibility and operational result of this installation?

  1. The B&M-keyed SATA SSD physically fits into slot M2_1 but will not be recognized by the system firmware, while the M-keyed NVMe SSD cannot physically insert into slot M2_2.Answer
  2. B
    Both SSDs physically fit into their respective slots, but the SATA SSD runs in AHCI mode while the NVMe SSD is throttled down to PCIe 3.0 x2 speed.
  3. C
    Neither drive physically fits into either slot due to keying protection mechanisms designed to prevent electrical damage.
  4. D
    The B&M-keyed SATA SSD operates normally in slot M2_1 by using PCIe lane emulation, but the M-keyed NVMe drive in slot M2_2 causes a POST beep error.

Answer

The B&M-keyed SATA SSD physically fits into slot M2_1 but will not be recognized by the system firmware, while the M-keyed NVMe SSD cannot physically insert into slot M2_2.
The correct option identifies both physical keying rules and logical bus routing constraints. A B&M-keyed drive has dual cutouts, enabling physical insertion into an M-key slot; however, because slot M2_1 lacks SATA traces, the drive receives power but cannot communicate with the system. An M-key drive has a single gap at pins 59-66, which physically prevents insertion into a B-key slot with a ridge at pins 12-19.

Step-by-Step Solution

1
Analyze the physical keying compatibility for slot M2_1 (M-key only) and the B&M-keyed SATA SSD.
A B&M-keyed SSD has pin cutouts at both positions 12-19 (B-key) and 59-66 (M-key), allowing it to physically insert into an M-key slot.
B&M keying provides universal physical insertion capability for legacy and multi-bus M.2 slots.
2
Analyze the electrical bus compatibility for slot M2_1 and the SATA SSD.
Slot M2_1 only routes PCIe lanes and lacks SATA controller trace connections.
Even though the drive physically fits, an M.2 SATA drive requires SATA controller signaling, so UEFI/BIOS cannot detect it.
3
Analyze the physical keying compatibility for slot M2_2 (B-key only) and the M-keyed NVMe SSD.
An M-keyed SSD only has a cutout at pins 59-66 and solid PCB at pins 12-19, which collides with the physical key bridge in a B-key slot.
Physical keying prevents inserting high-lane NVMe drives into B-key sockets that only support up to PCIe x2 or SATA.

Key Concept

M.2 Physical Keying vs. Electrical Bus Routing Compatibility
Estimated Time:2m 0s
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Topics

Storage Devices and Interfaces

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