Arm Instruction Set Architecture
A64 is the instruction set used in AArch64, supported by the Armv8-A, Armv8-R AArch64 and Armv9-A architectures.
Key features of A64 include:
Clean decode table based on 5-bit register specifiers. Instruction semantics broadly similar to A32 and T32. 31 general-purpose 64-bit registers accessible at all times. No modal banking of general purpose registers for improved performance and energy. Program counter and stack pointer are not general purpose registers. Dedicated zero register available for most instructions.