Armv8-A Instruction Sets
Armv8-A supports three instruction sets: A32, T32 and A64.
The A64 instruction set is used when executing in the AArch64 Execution state. It is a fixed-length 32-bit instruction set. The ‘64’ in the name refers to the use of this instruction by the AArch64 Execution state, it does not refer to the size of the instructions in memory.
The A32 and T32 instruction sets are used when executing in the AArch32 Execution state.
As a developer, you may not need to write directly in assembler in your day-to-day role. However, assembler is still important in some areas, such as the first stage boot software or some low-level kernel activities. Even if you are not writing assembly code directly, understanding what the instruction set can do, and how the compiler makes use of those instructions, can help you to write more efficient code. It can also help you to understand the output of the compiler, which can be useful when debugging.
The Arm Glossary provides a list of commonly used terms and descriptions of their meaning. Access this great resource to help your understanding of Arm documentation.