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Difficulty: MediumRAM Types and Characteristics

A technician is upgrading the memory on an enterprise rackmount server. The system documentation explicitly specifies that the motherboard requires Registered DIMMs (RDIMMs) to handle high-density memory configurations. The technician accidentally installs Unbuffered DIMMs (UDIMMs) of the same DDR generation and speed rating. Which statement correctly explains why the server fails to complete Power-On Self-Test (POST)?

  1. RDIMMs feature an onboard register that buffers control and address signals to reduce electrical load on the memory controller, whereas UDIMMs lack this register and cannot function in motherboards requiring buffered memory.Answer
  2. B
    UDIMMs utilize the smaller SO-DIMM physical form factor designed for laptops, causing a keying notch mismatch that prevents physical installation into server motherboard slots.
  3. C
    UDIMMs require memory modules to be installed into adjacent contiguous slots rather than alternating channel slots, causing a POST failure when placed in standard server slot configurations.
  4. D
    UDIMMs allow the system to complete POST normally but cause immediate operating system driver corruption during boot due to software-level memory buffering errors.

Answer

RDIMMs feature an onboard register that buffers control and address signals to reduce electrical load on the memory controller, whereas UDIMMs lack this register and cannot function in motherboards requiring buffered memory.
Registered memory (RDIMM) contains a dedicated hardware register chip that buffers command and address signals between the system memory controller and the memory modules. This reduces the electrical load placed on the memory controller, allowing servers to support larger quantities of RAM. Server motherboards specified for RDIMMs cannot communicate with Unbuffered DIMMs (UDIMMs), causing the system to fail POST.

Step-by-Step Solution

1
Identify the memory requirements of the system board.
The enterprise server board requires Registered DIMMs (RDIMMs).
Enterprise servers using high-density RAM configurations depend on signal registers to maintain signal integrity and manage electrical load on the CPU memory controller.
2
Compare RDIMM (Registered) architecture to UDIMM (Unbuffered) architecture.
RDIMMs include an extra register chip between the memory controller and DRAM, whereas UDIMMs connect directly to the memory controller without buffering.
Motherboards designed specifically for RDIMMs expect the register interface during system initialization; installing UDIMMs results in a hardware initialization failure.
3
Determine the system behavior during hardware boot.
The server fails the Power-On Self-Test (POST) before loading the operating system.
Incompatible memory architecture prevents the motherboard firmware from establishing valid communications with RAM during early boot checks.

Key Concept

Registered DIMMs (RDIMMs) vs. Unbuffered DIMMs (UDIMMs)
Estimated Time:1m 0s
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Topics

RAM Types and Characteristics

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