Best Dual-Channel RAM Slot Configuration
A technician is building a new PC for a video editor. The motherboard has four DIMM slots, labeled A1, A2, B1, and B2, and supports dual-channel memory. The technician installs two identical 8 GB DDR4 modules. Which of the following slot configurations will provide the BEST memory performance?
Quick Answer
The answer is A1 and B1, as this is the best dual-channel RAM slot configuration for maximizing memory performance on a standard four-slot motherboard. This works because dual-channel memory requires one module in each memory channel; slots A1 and A2 belong to channel A, while B1 and B2 belong to channel B, so placing a stick in A1 and B1 enables interleaved access that doubles memory bandwidth. On the CompTIA A+ Core 1 220-1101 exam, this question tests your understanding of motherboard memory architecture and the performance impact of channel configuration—a common trap is choosing adjacent slots like A1 and A2, which keeps both modules on the same channel and only runs in single-channel mode. For video editing workloads, higher throughput from dual-channel operation is critical, so remember the mnemonic: “A and B, one each, for double the reach.”
⚠ Common exam trap
Many candidates assume any two slots will work identically or that adjacent slots (A1/A2) are best, but CompTIA tests the specific requirement that dual-channel memory must use one slot per channel, typically the first slot of each channel (A1 and B1) for optimal performance.
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
✓
A1 and B1
(A1 and B1) is correct because dual-channel memory requires one module in each channel. On a typical motherboard with four slots, slots A1 and A2 belong to channel A, while B1 and B2 belong to channel B. Installing one module in A1 (channel A) and one in B1 (channel B) enables dual-channel interleaving, doubling the memory bandwidth compared to single-channel operation, which is critical for video editing workloads that benefit from higher throughput.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A1 and B2
Why it's wrong here
A1 and B2 do span both channels, but on most boards the matched pair for dual-channel is A1/B1 or A2/B2; A1/B2 can fall back to single-channel or fail to train. It tempts because the labels look like opposite channels, yet the correct pairing follows the board's slot-to-channel mapping.
- ✗
A1 and A2
Why it's wrong here
Slots A1 and A2 sit on the same memory channel, so the two modules interleave on one 64-bit path rather than two, halving peak bandwidth. It is tempting because populating adjacent slots is the conventional single-channel habit and boots fine, but dual-channel requires one module per channel — A1 with B1, or A2 with B2.
- ✓
A1 and B1
Why this is correct
Dual-channel operation requires the two matched modules to occupy different channels, so A1 and B1 populate separate channels and allow the memory controller to interleave accesses. Installing both in one channel (A1 and A2) would halve bandwidth, degrading the video editor's performance.
- ✗
Any two slots will perform identically
Why it's wrong here
Slot choice directly determines whether the memory controller interleaves across two 64-bit channels or runs one, so placement is not performance-neutral. It tempts because identical modules in any slots still POST and show full capacity, but bandwidth differs — dual-channel needs one DIMM per channel, not arbitrary slots.
Go deeper
Related to this question
Learn chapter
RAM Installation and Dual-Channel Configuration
Key term
Double Data Rate
Double Data Rate (DDR) is a technology that doubles the data transfer rate of a memory or bus by sending data on both the rising and falling edges of the clock signal, effectively doing twice as much work per clock cycle.
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).
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Same concept, more angles
1 more way this is tested on 220-1101
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A technician is building a workstation with a motherboard that has four DIMM slots arranged as two channels (slots 1/2 for channel A, slots 3/4 for channel B). The technician installs two identical 8 GB DDR4 modules in slots 1 and 2. The system POSTs successfully and shows 16 GB of RAM, but subsequent memory benchmarks indicate that the memory bandwidth is only half of the expected value. Which of the following should the technician do to resolve this issue?
medium- A.Enable XMP (Extreme Memory Profile) in the BIOS
- ✓ B.Move one of the RAM modules to slot 3
- C.Replace both modules with single-rank modules
- D.Increase the memory voltage in the BIOS
Why B: The motherboard has two memory channels: channel A (slots 1 and 2) and channel B (slots 3 and 4). Installing both modules in slots 1 and 2 places them on the same channel, which prevents dual-channel interleaving. This halves the memory bandwidth because the CPU can only access one module at a time per channel. Moving one module to slot 3 (channel B) enables dual-channel mode, doubling the effective bandwidth.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1101 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1101 exam.