Originally Posted by Shrimp
x64 is still x86. There's 32-bit x86 and 64-bit x86, for some reason they call 32-bit x86 and 64-bit x64.
The "x86" nomenclature comes from the chip's functional ID code. Chip makers back then already built support / system chips to be used with CPU chips. The chips were related in their ID codes as well. You had the 8088 which was an intel 8-bitter, later you had the 8086. For these CPUs there were support chips like parallel IO ports (8255), interrupt controllers (8253) and more of these. The digits '86' denoted the 16-bit CPU in the range of chips.
Then, better CPUs started to get around so intel started to up their version numbers into the ID: 80186, 80286, 80386 and so on. That 86 keeps returning untill Intel started to use the Pentium brand as chip ID. 80386 and 80486 were both 32 bits (although the 80386SX was a gimped 32-bit CPU with a 16-bit databus). Due to this numbering, the intel CPUs were referred to as the x86 family, where X could be anything from 80 up to 804.
Since the term x86 existed for a while it was only a matter of time before the 64-bit versions of the chip were termed x64 to make the distinction in bit-width within the Intel CPU family.
So... that's why x86 and x64 are seemingly unrelated