FAQ
TL;DR: If 16GB (2x8GB) shows as only 8GB, suspect a channel/slot issue; "the RAM controller is in the CPU." Reseat the CPU, check pins, and clear CMOS. This FAQ helps DDR3 desktop users fix a non-detecting second RAM slot. [Elektroda, 310artur, post #17094396]
Why it matters: A dead channel halves usable memory and can destabilize apps, games, and VMs.
Quick Facts
- 2x8GB showing as 8GB typically means one memory channel isn’t initializing; start with CPU and slot contacts. [Elektroda, 310artur, post #17094396]
- Typical DDR3 UDIMM: 240 pins, ~1.5 V; install matched pairs for dual-channel throughput. "Kingston DDR3 Memory Overview"
- Clear CMOS via the CLR_CMOS jumper; battery removal also works if you save BIOS settings first. [Elektroda, Mac!, #17094017]
- In this thread, straightening 1 bent CPU pin restored both slots to full 16GB. [Elektroda, Arabsky, post #17094472]
- If detection fails, reseat the CPU and inspect the RAM slot under magnification before replacing parts. [Elektroda, 310artur, post #17094313]
Why does only 8GB of my 16GB DDR3 show up?
One memory channel or slot failed to initialize. On AMD platforms, the memory controller sits on the CPU package. Bent pins, poor seating, or board faults can cause this. Swap modules and slots to isolate the path. Clear CMOS to retrain memory settings. [Elektroda, 310artur, post #17094396]
How do I quickly isolate the bad slot, stick, or channel?
Do a minimal swap test:
- Test each DIMM in Slot A by itself until it POSTs.
- Move the same DIMM(s) to Slot B and note any missing RAM.
- Install two DIMMs and swap positions; compare detection patterns.
[Elektroda, Mac!, #17094017]
Could the CPU be at fault when the second RAM slot fails?
Yes. On AMD Phenom/Athlon-era systems, "the RAM controller is in the CPU." A bent or misaligned pin can break one channel. Test with another CPU or board when possible. If the IMC channel dies, only CPU replacement resolves it. [Elektroda, 310artur, post #17094396]
What fixed it for the original poster here?
A single bent CPU pin was gently straightened. After reseating the CPU and clearing settings, both slots detected 16GB again. This points to contact integrity between CPU and socket as the root cause. [Elektroda, Arabsky, post #17094472]
How do I safely check and reseat the CPU?
Shut down, unplug power, and discharge by holding the power button. Remove the cooler and lift the CPU. Inspect the CPU pins and the socket using a magnifier and strong light. Reinstall the CPU carefully and reapply fresh thermal paste before mounting the cooler. [Elektroda, 310artur, post #17094313]
How do I clear CMOS properly?
Use the board’s procedure:
- With power unplugged, move the CLR_CMOS jumper to the clear position for 10–20 seconds.
- Move it back, reconnect power, and boot.
- Alternatively, remove the battery briefly, then restore BIOS settings.
[Elektroda, Mac!, #17094017]
Is the motherboard more likely bad than the CPU here?
Board faults are more common than CPU IMC failures, but there’s no certainty without testing. Avoid buying parts blindly. As one expert noted, “It pays off” to get a diagnosis first. [Elektroda, 310artur, post #17094396]
What if both sticks work in Slot A but not in Slot B?
That pattern indicates the Slot B path or its channel isn’t making contact. On AMD, inspect CPU pins carefully. In this thread, one bent pin caused the second slot to fail detection. [Elektroda, Arabsky, post #17094472]
Can dust or oxidation in the DIMM slot cause missing RAM?
Yes. Debris or oxidation can block contacts and prevent initialization. Blow out the slot with dry compressed air and inspect under magnification. Do not scrape the contacts. Reseat the module firmly until both latches click. [Elektroda, 310artur, post #17094313]
Will a BIOS update help detect both modules?
Sometimes. BIOS updates can improve memory training and SPD compatibility. Check your board’s support page, read the changelog, and flash only on a stable system. Back up settings before updating. "Crucial: Memory not recognized"
Is it safe to straighten a bent AMD CPU pin?
It can work, as shown in this case, but it’s risky and at your own risk. A slipped tool can snap a pin and render the CPU unusable. Use minimal force and precise tools if you proceed. [Elektroda, Arabsky, post #17094472]
Should I buy new RAM to fix this symptom?
No, not if both modules pass individually in one slot. That shows your DIMMs are fine. Focus on the second slot, CPU seating, pins, and CMOS reset before replacing hardware. [Elektroda, Arabsky, post #17094223]
What performance loss should I expect if I run single‑channel?
Expect an approximate 5–20% hit in memory‑sensitive workloads. Gaming, compression, and iGPU tasks may show the largest drops. Bandwidth‑light tasks might show less impact. "GamersNexus: Single vs Dual-Channel Memory Performance"
How should I install a 2x8GB DDR3 kit for dual‑channel?
Use the two matched‑color slots specified in your manual, often A2 and B2. Align the notch, press evenly until both latches click. Mixing slots incorrectly forces single‑channel operation and reduces bandwidth. "Kingston Memory Installation Guide"
You can try to remove and reinstall the CPU later (you will need to change the paste here). As well as that, it will not help to test the CPU on another board with 2 RAM bones or your set with a different CPU.
