Question 639 of 1,020

RAM →hardMultiple ChoiceObjective-mapped

Server RAM Upgrade Fails POST: Rank Compatibility

This 220-1201 practice question tests your understanding of ram. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

A server administrator needs to upgrade a critical database server from 64 GB to 128 GB of RAM. The server uses registered ECC DDR4 memory. They have purchased 8 x 16 GB registered ECC modules. When they install them, the server fails to POST with a memory error. The original 64 GB (4 x 16 GB) modules work fine. What is the most likely reason?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The new RAM modules are not compatible because they are not ECC, while the server requires ECC.
Why wrong: The scenario states the new modules are registered ECC, so this is not the issue.
B
The server's BIOS needs to be updated to support 128 GB.
Why wrong: If the server originally supported 128 GB (as stated), a BIOS update is unlikely needed. The problem is more specific to the modules themselves.
C
The new modules have a different number of ranks (e.g., dual-rank vs. single-rank) than the original modules, causing a rank mismatch that the memory controller cannot handle.
Servers are sensitive to rank configuration. Mixing single-rank and dual-rank modules, or using modules with a different number of ranks than the system expects, can prevent POST.
D
The new modules are not seated properly in the slots.
Why wrong: Improper seating is possible, but given that the original modules work and the new ones all fail, a systematic issue like rank mismatch is more likely.

Full breakdown with real-world context →

Quick Answer

The answer is a rank mismatch between the new and original memory modules. Registered ECC DDR4 memory relies on strict rank compatibility per channel; if the server originally used single-rank modules and the new 16 GB sticks are dual-rank, the memory controller may exceed its supported rank count when all eight slots are populated, causing the POST failure. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your understanding that server RAM upgrade fails POST rank compatibility is often due to mixing ranks or overloading the channel’s rank limit, not a simple capacity issue—a common trap is assuming all 16 GB modules are identical. Remember that rank is like lanes on a highway: more ranks per channel can jam the controller, so always verify the rank count in the server’s documentation before upgrading.

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

✓

The new modules have a different number of ranks (e.g., dual-rank vs. single-rank) than the original modules, causing a rank mismatch that the memory controller cannot handle.

Registered (buffered) ECC memory is designed for servers and has specific compatibility requirements, especially regarding the number of ranks per channel and the memory controller's capabilities. The most likely issue is that the new modules are of a different rank (e.g., dual-rank vs. single-rank) or the server's memory controller cannot handle the total number of ranks when all slots are populated. Mixing ranks or exceeding the rank limit per channel can cause POST failures.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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 new RAM modules are not compatible because they are not ECC, while the server requires ECC.
Why it's wrong here
The scenario states the new modules are registered ECC, so this is not the issue.
✗
The server's BIOS needs to be updated to support 128 GB.
Why it's wrong here
If the server originally supported 128 GB (as stated), a BIOS update is unlikely needed. The problem is more specific to the modules themselves.
✓
The new modules have a different number of ranks (e.g., dual-rank vs. single-rank) than the original modules, causing a rank mismatch that the memory controller cannot handle.
Why this is correct
Servers are sensitive to rank configuration. Mixing single-rank and dual-rank modules, or using modules with a different number of ranks than the system expects, can prevent POST.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The new modules are not seated properly in the slots.
Why it's wrong here
Improper seating is possible, but given that the original modules work and the new ones all fail, a systematic issue like rank mismatch is more likely.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.

Trap categories for this question

Scenario analysis trap
The scenario states the new modules are registered ECC, so this is not the issue.

Detailed technical explanation

How to think about this question

This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.

TExam Day Tips

Underline the problem statement mentally.
Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A practitioner preparing for the 220-1201 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.

What to study next

Got this wrong? Here's your next step.

Identify which 220-1201 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.

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FAQ

Questions learners often ask

What does this 220-1201 question test?

RAM — This question tests RAM — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The new modules have a different number of ranks (e.g., dual-rank vs. single-rank) than the original modules, causing a rank mismatch that the memory controller cannot handle. — Registered (buffered) ECC memory is designed for servers and has specific compatibility requirements, especially regarding the number of ranks per channel and the memory controller's capabilities. The most likely issue is that the new modules are of a different rank (e.g., dual-rank vs. single-rank) or the server's memory controller cannot handle the total number of ranks when all slots are populated. Mixing ranks or exceeding the rank limit per channel can cause POST failures.

What should I do if I get this 220-1201 question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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