Determining RAM slots in use on Linux

Posted on Wed 13 July 2016 in Linux

How many RAM slots do you have occupied and how many are free? Linux provides tools to inspect memory configuration without opening the computer.

dmidecode: The Main Tool¶

Basic Memory Information¶

# View all memory information
sudo dmidecode -t memory

# Specific memory type (table 16)
sudo dmidecode -t 16

# Installed sizes only
sudo dmidecode -t memory | grep -i size

Typical Output:

Size: 8192 MB
Size: 8192 MB
Size: No Module Installed
Size: No Module Installed

Detailed Information per Slot¶

# Granular information for each slot (table 17)
sudo dmidecode -t 17

# Compact summary
sudo dmidecode -t 17 | grep -E "(Size|Locator|Speed|Type:)"

Information Provided: - Locator: Physical slot identifier (DIMM_A1, DIMM_B1, etc.) - Size: Installed capacity or "No Module Installed" - Type: DDR3, DDR4, etc. - Speed: Speed in MT/s

lshw: Alternative with Structured Format¶

# Memory information with lshw
sudo lshw -class memory

# Physical memory only (no cache)
sudo lshw -class memory | grep -A 10 "System Memory"

# More compact format
sudo lshw -short -class memory

Useful Scripts for Analysis¶

Occupied Slots Counter¶

#!/bin/bash
echo "=== RAM Slot Analysis ==="
TOTAL_SLOTS=$(sudo dmidecode -t 17 | grep "Size:" | wc -l)
OCCUPIED_SLOTS=$(sudo dmidecode -t 17 | grep "Size:" | grep -v "No Module" | wc -l)
FREE_SLOTS=$((TOTAL_SLOTS - OCCUPIED_SLOTS))

echo "Total Slots: $TOTAL_SLOTS"
echo "Occupied Slots: $OCCUPIED_SLOTS" 
echo "Free Slots: $FREE_SLOTS"

Detailed Summary¶

#!/bin/bash
echo "=== Current RAM Configuration ==="
sudo dmidecode -t 17 | awk '
/Memory Device/,/^$/ {
    if(/Locator:/) locator=$2
    if(/Size:/ && !/No Module/) {
        size=$2" "$3
        print locator": "size
    }
    if(/Size:.*No Module/) print locator": Empty"
}'

Additional Useful Information¶

Maximum Supported Capacity¶

# Maximum total capacity
sudo dmidecode -t 16 | grep "Maximum Capacity"

# Maximum number of devices
sudo dmidecode -t 16 | grep "Number Of Devices"

Speed and Type Verification¶

# Configured speed
sudo dmidecode -t 17 | grep -E "(Speed|Configured)"

# Memory type
sudo dmidecode -t 17 | grep "Type:" | grep -v "Error"

Example of Interpreted Output¶

$ sudo dmidecode -t 17 | grep -E "(Locator|Size|Type:)" | head -12

Locator: DIMM_A1
Size: 8192 MB  
Type: DDR4

Locator: DIMM_A2
Size: No Module Installed
Type: Unknown

Locator: DIMM_B1  
Size: 8192 MB
Type: DDR4

Locator: DIMM_B2
Size: No Module Installed
Type: Unknown

Interpretation: - 4 total slots (DIMM_A1, A2, B1, B2) - 2 slots occupied with 8GB DDR4 each - 2 free slots available

Important Limitations¶

⚠️ Accuracy: Command-line tools may not perfectly reflect physical hardware

⚠️ Privileges: Root permissions are required to access DMI information

⚠️ Compatibility: Some embedded systems may not provide complete information

For maximum certainty, physical inspection is still recommended, but these tools provide sufficiently accurate information for most cases.

Original source: Unix & Linux Stack Exchange

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