220-1101 Hardware Practice Question
A technician builds a new PC and installs two 8GB DDR4 RAM modules from the same kit into the appropriate slots on the motherboard. The system boots and the BIOS reports only 8GB of total memory. The technician has reseated the modules and verified they are fully inserted. The motherboard manual indicates that the slots used are correct for dual-channel configuration. Which of the following is the MOST likely cause?
⚠ Common exam trap
Many exam-takers assume a damaged motherboard slot or incompatibility when the symptom is simply half the expected memory, but the most common cause in a new build with matched modules is a defective stick.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
One of the RAM modules is defective.
The system detects only 8GB of total memory despite having two 8GB modules installed. Since both modules are from the same kit and the slots are confirmed correct, the most likely cause is that one of the modules is defective. A faulty module will not be recognized by the BIOS, resulting in half the expected capacity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The RAM modules are not compatible with the CPU.
Why it's wrong here
DDR4 memory is backward/forward compatible within its generation, but if the CPU's memory controller does not support a particular module spec (e.g., ECC, registered, or excessively high frequency), the system may fail to POST or exhibit blue screens, not simply ignore one module. Since both modules are identical, a compatibility problem would typically affect both sticks equally, causing either a shutdown or a complete failure to recognize any memory, rather than halving the capacity.
- ✓
One of the RAM modules is defective.
Why this is correct
A physically damaged or internally faulty module may fail to respond to the system's SPD interrogation or memory training, so the BIOS skips it and reports only the capacity of the functional stick. This is a common occurrence when one DIMM has a cracked trace, failed DRAM chip, or corrupted SPD—allowing the other module to operate normally while the defective one is completely omitted. The result is exactly half the installed RAM, making a defective module the most probable cause.
- ✗
The motherboard's memory slot is damaged.
Why it's wrong here
A damaged memory slot (e.g., bent pins, broken solder joint) typically prevents that entire channel from passing memory training, which usually results in a no-POST beep code or the system refusing to boot, not merely ignoring one stick while using the other. If the slot is completely dead, the BIOS may still boot using only the other slot, but that would also require the module to be seated differently; a slot defect is far less common than a defective DIMM on a brand-new build, and it would likely affect both slots if the damage were to the shared memory bus.
- ✗
The RAM is running at the wrong voltage.
Why it's wrong here
Running DDR4 at an incorrect voltage (e.g., setting 1.35V manually on a 1.2V board) can cause instability, random reboots, or memory training errors, but it would not cause the BIOS to permanently detect only one of two otherwise identical modules. Voltage errors are global to the memory subsystem—both sticks receive the same VDDQ—so both would be equally affected; the system would typically show errors or fail to boot rather than silently dropping one module's capacity.
Go deeper
Related to this question
Learn chapter
RAM Types and Memory Slots
Key term
Dual In-line Memory Module
A Dual In-line Memory Module (DIMM) is a small circuit board that holds memory chips and plugs into a computer's motherboard to provide Random Access Memory (RAM).
Key term
RAM
RAM (Random-Access Memory) is volatile computer memory that temporarily stores data for quick access by the CPU.
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Written by Johnson Ajibi, MSc IT Security
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