Comment by dfox

IIRC it is slightly more complex: the Tru64 callPAL API is the common subset of all the three variants (VMS/Tru64/NT), but the NT/AlphaBIOS has slightly incompatible ABI which Linux can detect and work around. And also IIRC original Linux port to Alpha expected the NT PALcode, which makes sense given the fact that DEC sold systems that didn't have SRM in PROM (ie. Multia and a-series PWS) and thus only supported NT or Linux.