WhyAmIgettingMemoryErrors

To help understand why you are seeing memory errors, please have a look at HowMemoryEdacHardwareWorks.

You may well have been experiencing these errors for a while, it's just that nothing was checking them until you enabled the EDAC module. Note that your system is probably experiencing data corruption (if you are getting UEs - uncorrectable errors), so you should really check this out (this is why EDAC is set to `panic()` on UEs by default).

The reason that you are seeing problems is very likely to be one of:

• Your RAM is bad
• Your Motherboard is bad
• Your CPU is bad (for CPUs which have the memory controller built into the CPU core, such at the AMD Opteron/Athlon-64)
• The connection between your motherboard and your CPU, or memory module is bad
• Some of your hardware is being operated outside of its design specification, such as:
  • Things are being run too hot
  • Timings are being violated (e.g. running memory too fast, or bad DRAM clock generation)
  • Supply voltages to the critical compontents are too high/low (this may even happend very briefly, as a supply "spike", or "droop")
• You have seen one or more "Single Event Upsets" - see SoftErrors
• Memory ECC check bits are not properly initialised by BIOS prior to Linux boot
• The EDAC module is buggy
• Memory loading is exceeded

So Which One Is It Then?

Good question. Time to try some things:

Symptoms

Here are the most likely symptoms.

Problem	Error Addresses	Error Slot or Row	Error Frequency
Bad Memory Module(s)	Single/Few	Probably only 1	May vary if part is marginally out of spec
Bad Motherboard	Probably many	Maybe 1, maybe many	?
Bad Connection	Probably many	1 (bad mem), prob all (bad CPU)	?
Temp out of spec	Probably few	Maybe one, if different mem mfrs/parts	Usually higher, with higher temp
Timings out of spec	Probably few	Maybe one, if different mem mfrs/parts	Usually higher, with higher temp
Voltages out of spec	Probably random	Maybe one, if different mem mfrs/parts	Usually higher at higher system load
Bad check bit init	Probably random	Probably all	High/very high (stops after a while for systems with background scrub)
Single event upsets	Random	Varies with effective "cross-section" of part	Very rare

Things to try to isolate the problem

General:

• Get a second opinion e.g. from [[1]] or [[2]] - note that you should be sure that either:
  • The memory testing software knows how to disable ECC on your system, or
  • You have disabled ECC before running memory tester (note that memtest86 currently displays "ECC: No" on chipsets which have ECC, but which it doesn't know about!)
• This may not catch problems like power-supply related problems, which don't occur when the memory tester is running
• Use a system stress tester such as "burnbx" from [[3]]
• Put your system under stress by (e.g.) running a parallelised Linux kernel build, whilst doing some heavy 3D graphics display, and a lot of disk I/O

Suspected bad module:

• Remove Module
• Move Module to different slot (do errors move with module)
• Move Module to different machine
• See "suspected temp out of spec"
• See "suspected timings out of spec"
• See "voltages out of spec"
• Clean connections
• Check Memory Loading
  • Some memory controllers can only support so many 'ranks' of memory at a given speed.

    For example, Opterons/Athlon64s can support only 4 ranks of 2 GB at PC3200. 
    See http://www.valueram.com/memoryranks/default.asp for definitions.

Suspected bad motherboard:

• Check motherboard docs for memory module compatability
• Move modules to different slots
• Clean connections
• Upgrade BIOS
• Select BIOS "fail-safe defaults", or equivalent change settings from there to isolate cause

Suspected bad connection:

• Visually check connectors, pins, modules etc.
• HowToCleanEdgeConnectors

Suspected temp out of spec:

• Measure temp, compare to published specs:
  • Use internal machine sensors (motherboard, hard drive etc.) if possible
  • Use a temperature probe
• Check airflow
• De-dust
• Lower temp:
  • Lower room temp
  • Increase cooling
  • Improve airflow (tidy cables etc.)

Suspected timings out of spec:

• Try different BIOS version
• Set pessimistic memory timings in BIOS
• Compare memory controller timings to DIMM specs, using decode-dimms.pl from the Linux i2c project
• Try disabling "spread spectrum" in the BIOS (easy), or by using an i2c driver for your board's clock generator (hard)

Suspected voltage out of spec:

• Check PSU specs vs. total demand of system components
• Swap power supply with another machine
• Fit voltage regulator/spike surpressor to machine power supply

Suspected single event upsets:

• Fit less susceptible components
• Move to a lower altitude, or area with lower cosmic radiation
• Move your data centre underground
• Improve error-reporting utilities to ignore them

Suspected bad check-bit init:

• Upgrade BIOS
• Don't enable BIOS "quick boot"
• Don't manually skip BIOS memory check