On a 64-bit machine running in 64-bit mode:
echo %programfiles%
==> C:\Program Files
echo %programfiles(x86)%
==> C:\Program Files (x86)
On a 64-bit machine running in 32-bit (WOW64) mode:
echo %programfiles%
==> C:\Program Files (x86)
echo %programfiles(x86)%
==> C:\Program Files (x86)
On a 32-bit machine running in 32-bit mode:
echo %programfiles%
==> C:\Program Files
echo %programfiles(x86)%
==> %programfiles(x86)%