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Difficulty: Very hardStorage Devices and Interfaces

A system technician is building a custom workstation for video editing using a motherboard equipped with two M.2 expansion slots labeled Slot 1 and Slot 2. The motherboard manual specifies that Slot 1 is wired directly to the CPU's dedicated PCIe 4.0 x4 bus lanes and does not support SATA signaling, while Slot 2 connects to the chipset supporting both PCIe 3.0 x2 and SATA 3.0 protocols. The technician installs a new M.2 SATA SSD into Slot 1 and a high-speed M.2 NVMe SSD into Slot 2. When the computer is powered on, the system UEFI/BIOS detects the NVMe SSD in Slot 2, but the SATA SSD in Slot 1 is not recognized anywhere in the storage configuration menu. Which of the following best explains why the drive in Slot 1 is not detected?

  1. Slot 1 is a PCIe-only M.2 slot that lacks physical circuit routing to the host SATA controller.Answer
  2. B
    M.2 SATA SSDs require AHCI mode to be explicitly disabled in the system firmware to operate over PCIe lanes.
  3. C
    Installing an NVMe SSD into Slot 2 automatically disables all SATA protocol signaling across all system M.2 slots.
  4. D
    The M.2 SATA SSD requires a PCIe x4 lane connection to negotiate initial handshake frequencies with the CPU.

Answer

Slot 1 is a PCIe-only M.2 slot that lacks physical circuit routing to the host SATA controller.
The correct answer identifies that Slot 1 is connected exclusively to PCIe CPU lanes and lacks motherboard trace routing to a SATA controller. While M.2 specifies the physical connector shape, the storage protocol (SATA vs. NVMe/PCIe) depends on how the specific slot is wired. An M.2 SATA drive installed in a PCIe-only slot will receive power but cannot establish data communication.

Step-by-Step Solution

1
Analyze the specifications for Slot 1 and Slot 2 provided in the scenario.
Slot 1 only connects to dedicated PCIe lanes from the CPU, whereas Slot 2 connects to the chipset with support for both PCIe and SATA protocols.
M.2 is a physical form factor that can carry different electrical signals (PCIe/NVMe, SATA, or USB) depending on how the motherboard manufacturer wires the slot.
2
Evaluate the drive type installed into Slot 1.
An M.2 SATA SSD was placed into Slot 1.
An M.2 SATA SSD requires a SATA controller connection on the motherboard to transmit data using the SATA protocol.
3
Determine why the SATA SSD fails to function in Slot 1.
Because Slot 1 carries only PCIe bus signals and has no connection to the motherboard SATA controller, the SATA drive cannot communicate with the system.
Physical mechanical insertion (such as B+M keying compatibility) does not guarantee protocol compatibility if the host slot lacks SATA wiring.

Key Concept

M.2 Interface Protocols vs. Form Factor Compatibility
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Topics

Storage Devices and Interfaces

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