Although Microsoft is by far the dominant player in the Wintel partnership now, Intel's continuing influence should not be underestimated. Intel and Microsoft, once the closest of partners, have operated at an uneasy distance from one another since their first major dispute, which had to do with Intel's heavy investment in the 32-bit optimized Pentium Pro and Microsoft's delivery of an unexpectedly high proportion of 16-bit code in Windows 95. Both firms talk with one another's competitors from time to time, most notably with Microsoft's close relationship with AMD and the development of Windows XP Professional x64 Edition utilizing AMD-designed 64-bit extensions to the x86 architecture, and Intel's decision to sell its processors to Apple Inc.