quote: Fundamental to ARMv8 has to be the new instruction set, known as A64; the encoding of instructions to enable an application to utilize a 64-bit machine. ARM took the decision to introduce 64-bit through a new instruction set rather than extension of an existing instruction set for many good reasons. Most notably, and probably as no surprise, because we could develop a new independent instruction set to execute code in a lower power manner than by adding instructions to the existing instruction set. Of course, for compatibility reasons, we still support the entire ARMv7 machine in the new ARMv8 architecture, but when running 64-bit software, this part of the machine is not being used, and the area of complex legacy it had built up does not need to be active when running in the 64-bit ISA, unlike other architectures where 64-bit extension was simply added to the historical complexity and legacy of their 32-bit mode.
quote: I think we all know who the "other architectures where 64-bit extension was simply added to the historical complexity and legacy of their 32-bit mode" are.