Memtest86

Memtest86+ is software designed to stress test an 86-compatible computer's random access memory (RAM) for errors. It tries to verify that the RAM will accept and correctly retain arbitrary patterns of data written to it.

[edit] Description

Memtest86+ is designed to run from a bootable floppy disk, CD-ROM, USB Drive, or from a suitable bootloader without an operating system present. Memtest86+'s tests are comprehensive so it can find otherwise hidden problems on machines that appear to work normally. With many chipsets, Memtest86+ allows counting of failures even in error-correcting ECC DRAM.

Additionally, versions after 1.60 can output a list of bad RAM regions in the format expected by the BadRAM[1] patch[2] for the Linux kernel; using this information, a Linux system can reliably use a RAM module even if it has a few bad bits.

Memtest86 was originally developed by Chris Brady; Memtest86+ is developed by Samuel Demeulemeester. After several years of a development standstill, both are actively worked on. The bootloading code was originally derived from Linux 1.2.1. Memtest86 is written in C and x86 assembly. The source code is released under the GNU General Public License (GPL). The current version of Memtest86 is v3.5, released on January 3, 2009 and v2.11 of Memtest86+, released on December 22, 2008. Both versions now support current dual- and quad-core-CPU's and the corresponding chipsets. The latest release of Memtest86+ supports Intel-based Macintosh computers.

[edit] How it works

Memtest86+ writes a series of test patterns to every memory address, reads back the data written, and compares it for errors.

Many chipsets can report RAM speeds and timings via SPD (Serial Presence Detect) or EPP (Enhanced Performance Profiles), and some even support changing the expected memory speed. If the expected memory speed is overclocked, Memtest86+ can test that memory performance is error-free with these faster settings.