quote: x86-64 (also known as x64) is a 64-bit extension of IA-32, the 32-bit generation of the x86 instruction set. It supports vastly larger amounts of virtual memory and physical memory than is possible on IA-32, allowing programs to store larger amounts of data in memory. x86-64 also provides 64-bit general purpose registers and numerous other enhancements. The original specification was created by AMD, and has been implemented by AMD, Intel, VIA, and others. It is fully backwards compatible with 16-bit and 32-bit x86 code.(p13-14) Because the full x86 16-bit and 32-bit instruction sets remain implemented in hardware without any intervening emulation, existing x86 executables run with no compatibility or performance penalties, whereas existing applications that are recoded to take advantage of new features of the processor design may achieve performance improvements.
quote: As the term became common after the introduction of the 80386, it usually implies binary compatibility with the 32-bit instruction set of the 80386. This may sometimes be emphasized as x86-32 or x32 to distinguish it either from the original 16-bit "x86-16" or from the 64-bit x86-64.  Although most x86 processors used in new personal computers and servers have 64-bit capabilities, to avoid compatibility problems with older computers or systems, the term x86-64 (or x64) is often used to denote 64-bit software, with the term x86 implying only 32-bit. 
quote: So you're both going to pretend that the convention isn't to use "x86" to refer to 32-bit stuff and "x64" to refer to 64-bit stuff?
quote: illiteratehack writes "10 years ago AMD released its first Opteron processor, the first 64-bit x86 processor . The firm's 64-bit 'extensions' allowed the chip to run existing 32-bit x86 code in a bid to avoid the problems faced by Intel's Itanium processor. However AMD suffered from a lack of native 64-bit software support, with Microsoft's Windows XP 64-bit edition severely hampering its adoption in the workstation market." But it worked out in the end.
quote: I have more expertise about computer hardware in my left pinky than either of you children will ever learn.
quote: The insistence of toddlers that long-established norms like x86 vs. x64 to denote 32-bit vs. 64-bit somehow never existed