Glossary

Machine Check

An hardware error detected by hardware and reported to software.

Machine Check Architecture (MCA)

x86 machine check architecture is a hardware programming interface to allow software to report and handle both corrected and uncorrected hardware errors. This is an architectural interface with some abstraction and allows forwards and backwards compatible operating systems. Details are described in the Intel Architecture Software Developer Manual Volume 3 chapter 15.

Machine Check Exception (MCE)

The x86 CPU raises an int 18 exception to signify an uncorrected hardware error. The operating system has a special handler to process the information contained in the MCA registers

ECC

Error Correcting Code. A specific code that can detect and correct errors. Typical ECC codes can detect two bit of errors and correct one bit (there are some advanced encodings that can handle more errors). See Wikipedia's ECC entry. On servers the memory subsystem generally supports ECC.

Corrected error

An hardware error that was corrected by the hardware (e.g. using a single bit data corruption that was correctible using ECC). These errors do not require immediate software actions, but are still reported for accounting and predictive failure analysis.

Uncorrected error

An uncorrected hardware error detected by the hardware. Data corruption has occurred. These errors require software reaction.

Predictive Failure Analysis (PFA)

Using trends in (primarily) corrected errors to predict future failure of hardware components and automatically taking steps to avoid outages. mcelog implements automatic offlining for memory, CPU caches. Additional user-specified actions can be also configured.

IO-MCA

Used for reporting uncorrected errors on PCI Express links on newer Xeon systems. Supported by mcelog, see IO errors.

PCI AER

PCI-Express Advanced Error reporting. Used for error reporting on PCI Express links. Not supported by mcelog, but logged to the normal kernel log. For more details one the implementation see the OLS paper. See also IO-MCA.

RAS

Reliability, Availability, Serviceability.

DIMM

Memory module.

DMI (or SMBIOS)

This is a standardized way for a BIOS to report the current hardware configuration to the operating system. The DMI information can be dumped with the dmidecode program. mcelog uses this information when available to map DIMM numbers to silk screen labels.

APEI

An interface defined the ACPI 4 standard that allows a BIOS to report errors to an operating system. Formerly known as WHEA.

EDAC

An alternative memory error reporting framework. See the FAQ entry