Armv8A

ARMv8A (often written as ARMv8-A) is the ARM architecture version that introduced a 64-bit execution state while preserving backward compatibility with 32-bit software. Developed by ARM Holdings, it was released in 2011 to address the needs of high-performance and mobile devices, offering improved energy efficiency, security, and scalability.

A central feature of ARMv8-A is the AArch64 execution state, which provides a 64-bit instruction set, 64-bit general-purpose registers, and an expanded address space, along with enhancements to floating-point and vector processing. At the same time, ARMv8-A retains a backward-compatible AArch32 state that allows running 32-bit ARM software in a separate mode, enabling a gradual transition for software ecosystems.

The architecture defines four exception levels (EL0 to EL3), enabling a structured separation between applications, operating systems, and the hypervisor. TrustZone security extensions create a secure world for cryptographic keys and trusted operations, improving isolation and secure boot capabilities.

ARMv8A supports hardware-assisted virtualization with an EL2 hypervisor level and mechanisms to manage guest operating systems efficiently, including Stage-2 translation for guest memory. In terms of memory, AArch64 uses a multi-level page table scheme with support for multiple page sizes, enabling robust isolation, caching behavior, and scalable memory management across cores.

In addition to the 64-bit core, ARMv8-A includes optional features such as Advanced SIMD (NEON), improved floating-point capabilities, and Crypto Extensions for hardware-accelerated cryptography. It supports multicore and heterogeneous designs, commonly implemented as big.LITTLE configurations in Cortex-A processors.

ARMv8-A formed the foundation for modern 64-bit ARM CPUs in mobile and embedded markets and remains a reference point for future ARM architecture updates, including ARMv9.