Windows 8.1 64 Bit Not Working With Some Old AMD Processors

Microsoft recently made a statement to Neowin confirming that some really old AMD processors would experience issues running Windows 8.1 64 bit. Microsoft claim that some early AMD processors (such as the Athlon 64, Athlon x2 64, Opteron 185) cannot run Windows 8.1 64 bit due to the fact they are missing the CMPXCHG16b instruction set. Windows 8 64 bit did not pose the same problem as that OS had a special software implementation that meant these older CPUs still worked. Microsoft has since removed that support in Windows 8.1 64 bit. Old AMD CPU owners could still run 32 bit Windows 8.1 without any issues, just not the 64 bit.

“This was a change done to improve the security effectiveness of Windows by removing code that cannot use instructions such as CMPXCHG16b. Based on our data, the number of affected processors are extremely small, since this instruction has been supported for greater than 10 years.”

While its never nice to see support for hardware dropped from an OS, the fact most of these unsupported processors date from 2002-2006 suggests that if you’re still running them it really is time for an upgrade. If you’re a die hard “non-upgrader” then you’ll have to stick to 32 bit for now.

Image courtesy of AMD