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Difficulty: HardRAM Types and Characteristics

A technician is tasked with installing RAM into a rackmount server whose motherboard chipset requires Registered DIMMs (RDIMMs) with Error-Correcting Code (ECC). The technician purchases and installs standard Unbuffered ECC DIMMs (ECC UDIMMs) of identical speed, pin count, and capacity. Upon powering on the system, the server fails to complete POST and emits a continuous beep code indicating a memory error. Which of the following best explains why the server failed to start?

  1. The motherboard memory controller cannot interface with unbuffered ECC modules because RDIMMs use a register chip to buffer control and address signals.Answer
  2. B
    The memory modules were installed into adjacent slots across different channels rather than populating alternating slots designated for dual-channel architecture.
  3. C
    The technician selected SO-DIMM form-factor modules that do not fit standard full-sized server motherboard expansion slots.
  4. D
    The motherboard requires non-ECC memory modules because ECC functionality is only supported when using SO-DIMM form factors.

Answer

The server failed to boot because the motherboard chipset specifically requires Registered DIMMs (RDIMMs). Unbuffered ECC modules (ECC UDIMMs) lack the dedicated register chip needed to buffer electrical loads on control and address lines, making them electrically incompatible with motherboards that mandate RDIMMs.
Registered DIMMs (RDIMMs) feature an onboard hardware register that buffers address and control signals between the memory modules and the memory controller. This buffering reduces electrical loading on the controller, allowing systems to support high memory capacities and densities. Motherboards designed exclusively for RDIMMs cannot operate with Unbuffered DIMMs (UDIMMs)—even if those UDIMMs support ECC—because the electrical signaling and memory controller configuration differ fundamentally.

Step-by-Step Solution

1
Analyze the hardware requirements specified for the server motherboard.
The server motherboard mandates Registered DIMMs (RDIMMs) with ECC capability.
Registered memory places a hardware buffer (register) between the RAM module and the system memory controller to stabilize electrical loads in high-density server configurations.
2
Compare the installed memory modules with the motherboard's requirements.
The technician installed Unbuffered ECC DIMMs (ECC UDIMMs).
Although both RDIMMs and ECC UDIMMs support error checking and correction, UDIMMs lack the register chip required by registered-memory system architectures.
3
Determine the cause of the POST memory failure.
The memory controller cannot establish proper signal timing or communication with the unbuffered modules.
Mixing memory buffering types or using UDIMMs in an RDIMM-only motherboard prevents POST completion.

Key Concept

Registered RAM (RDIMM) vs. Unbuffered RAM (UDIMM) Compatibility
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Topics

RAM Types and Characteristics

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