Memtest86+ v1.70 released on 14 January 2007 (freeware, no adware, no spyware):
http://www.memtest.org/

Enhancements in v1.70 :

* New Features
o Add new DMI polling feature
o Add Support for Core/Core2 Solo/Duo/Quad CPU
o Add Support for AMD K8 with DDR2 Memory
o Add Support for Intel CPU with 192/384 KB L2 Cache
o Add Support for FB-DIMM based memory (DMI)
o Add Detection for ALI CyberAladdin-T (M1644)
o Add Detection for Turion 64 X2
o Add Support for ATi Radeon xPress 3200
o Add Support for Intel i975X
o Add Support for Intel Q965/P965
o Add Support for Intel Q963/Q965

* Bug Fixes
o Force detection for AMD K8 with unknown chipsets

This is really good software, but be carefull! Sometimes it makes changes wich aren't good.

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Sorry? It makes changes to... Where?

It's indeed a very good piece of software. Has helped me and many others numerous times in troubleshooting hardware problems. It seems that many computers, at least here in Finland, suffer from same problem: Electrity has some interrupts here and there. Motherboard gets power too much ---> RAM chips or hard-drive die second. And then we have this faulty operating computer. With memtest86+, I can find problems with RAM very easily and reliably =).

You need to elude to what you're talking about, changes to what?
All it does is create a bootable floppy disk, or bootable CD to check for faulty memory - and if you have problems with it do report it!