RAM appearing in bios and memtest86+* but not usable? (Linux Mint)

Understanding RAM Visibility and Usability Issues on Linux Mint: A Step-by-Step Guide

Introduction

Upgrading RAM is a common method to boost system performance, but sometimes, even after physically installing new modules, users encounter challenges with the operating system recognizing or utilizing the full memory capacity. This guide explores a real-world scenario involving Ubuntu-based Linux Mint 22.1 Cinnamon, providing insights and troubleshooting steps to resolve RAM detection and usability issues effectively.

Scenario Overview

A user recently expanded their system’s RAM from 16GB to 32GB by adding two additional DDR4 sticks, each of 8GB, bringing the total to four modules. Despite all sticks being from the same brand and capacity, the system exhibits discrepancies:

BIOS Recognition: All RAM sticks are correctly detected and displayed in the system firmware.
Memory Testing: Memtest86+ identifies all four modules individually.
OS Reporting: Only 16GB of RAM is visible and usable within Linux Mint and system monitoring tools.

System Specifications

Operating System: Linux Mint 22.1 Cinnamon
Kernel: 6.8.0-71-generic
Motherboard: ASRock B450 Pro4
CPU: AMD Ryzen 5 2600 Six-Core Processor
Graphics Card: Radeon RX 6600 XT

Initial Observations

The BIOS correctly detects all four RAM modules.
Memtest86+ passes with all four sticks recognized, although only 16GB are tested at a time.
The OS and system monitoring tools report only 16GB of usable memory.
Previous attempts to troubleshoot included reseating the RAM modules and observing system stability issues like stuttering and crashes.

Potential Causes and Troubleshooting Steps

Check Memory Seating and Hardware Compatibility
Ensure all RAM sticks are firmly seated in their slots.
Verify that the modules are installed in the correct slots as per the motherboard manual to enable dual-channel operation, which can sometimes influence memory recognition.
Inspect BIOS Settings
Confirm that memory-related settings are set to default or auto configurations.
Disable any memory overclocking features or XMP profiles temporarily to test default operation.
Verify Kernel and System Recognition
Use commands such as dmesg, lshw -c memory, and free -h to gather detailed information about detected RAM.
For instance, run `sudo dmidecode