MemTest86 is the original, free, stand alone memory testing software for x86 and ARM computers. hago123 link

MemTest86 boots from a USB flash drive and tests the RAM in your computer for faults using a series of comprehensive algorithms and test patterns. If you provide more context or specifics about

Unreliable RAM can cause a multitude of problems. Corrupted data, crashes and unexplained behaviour. hago123 link

Bad RAM is one of the most frustrating computer problems to have as symptoms are often random and hard to pin down. MemTest86 can help diagnose faulty RAM (or rule it out as a cause of system instability). As such it is often used by system builders, PC repair stores, overclockers & PC manufacturers.

Free, Professional or Site Edition

Since MemTest86 v5, the software is offered as a Free edition, or as a paid for Pro and Site edition. The Pro edition offers a number of additional features such as customizable reports & automation via a configuration file. The Site edition includes all features in the Pro Edition but also supports scalable deployment of MemTest86 across LAN via PXE boot.