Difference between ia64 and x64
According to this page:
IA64 refers to the 64 bit Itanium architecture while x64 is the 64 bit extension to the x86 architecture.
The IA64 is exclusive to Intel while x64 is used by all.
IA64 was intended for high-end server applications while x64 was initially intended for desktops but were scaled up.
IA64 systems are not able to run old x86 applications while most x64 systems are.
IA64 is very slow to adopt new computer technologies while x64 is very fast.
IA64 would no longer be supported by newer versions of Microsoft Windows while the x64 would still be supported.
"ia64" is Itanium, a server CPU architecture Intel created around 2000 incompatible with the "x86" processors in wide use on desktop systems. Itanium was supposed to be "next best thing" but it proved not to bring the performance benefits that it was touted to have. It is on the way out.
x64 is a vendor-neutral/Microsoft term for 64-bit CPUs. A lot of Linux people will use the term "amd64" instead because AMD was the one that first came out with CPUs that extended the Intel "x86" 32-bit instruction set and architecture to 64 bits (rather than developing a new, incompatible 64-bit processor).