Published on 2025-09-27. Introduction In the late 1900s, Intel was fully invested in Itanium (IA-64) being their future 64bit architecture. At that time (allegedly around 1997-1998), some Intel engineers – who were more cautious than their management – built a 64bit extension for their x86 processors as a backstop. It never shipped: Intel’s Pentium 4 had our own internal version of x86–64. But you could not use it: we were forced to “fuse it off”, meaning that even though the functionality was i...