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Difficulty: HardRAM Types and Characteristics

A technician is installing memory modules into a newly assembled desktop workstation motherboard equipped with four DDR4 memory slots configured into two distinct channels: Channel A (slots A1 and A2) and Channel B (slots B1 and B2). The motherboard documentation specifies that populating matching modules into slots A2 and B2 is required for optimal performance. If the technician mistakenly populates two identical 16 GB DDR4 UDIMMs into adjacent slots A1 and A2 instead, which of the following best describes the resulting system behavior?

  1. The system will complete POST and detect all 32 GB of RAM, but the memory controller will operate strictly in single-channel mode, reducing peak memory throughput.Answer
  2. B
    The system will fail Power-On Self-Test (POST) and halt with a memory error beep code because DDR4 UDIMMs cannot function when installed in adjacent physical slots.
  3. C
    The motherboard memory controller will automatically disable the module in slot A2 to prevent timing instability, reporting only 16 GB of available capacity.
  4. D
    The system will successfully boot into dual-channel mode, but it requires replacing the installed desktop memory with SO-DIMM modules to allow adjacent slot configurations.

Answer

The system will complete POST and recognize the full 32 GB memory capacity, but it will operate in single-channel mode rather than dual-channel mode.
Modern motherboard memory controllers support running multiple memory modules on a single channel. When both modules are placed in slots A1 and A2, they reside on Channel A alone. The system boots normally and recognizes the combined 32 GB capacity, but memory communication is restricted to single-channel bandwidth rather than achieving interleaving across dual channels (Channel A and Channel B).

Step-by-Step Solution

1
Analyze the slot placement described in the scenario.
The technician placed memory sticks into slots A1 and A2, which belong entirely to Channel A.
Dual-channel architecture requires at least one module populated in Channel A and one module populated in Channel B.
2
Determine the impact on system initialization and detected capacity.
Both 16 GB modules are operational on Channel A, providing a total detected capacity of 32 GB.
Populating multiple modules on a single channel is fully supported by system hardware and does not fail POST.
3
Evaluate memory performance and throughput characteristics.
The system operates with a single 64-bit wide data bus (single-channel mode).
To double memory bandwidth via dual-channel performance (128-bit total width), modules must be populated across separate channels (such as A2 and B2).

Key Concept

Dual-Channel Memory Architecture and Slot Population Rules
Estimated Time:2m 0s
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Topics

RAM Types and Characteristics

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