- v4 is the oldest supported architecture today. It added:
- Load/store instructions for signed and unsigned halfwords and bytes.
- System mode – privileged mode using user registers.
- 26-bit addressing no longer supported.
- v4T added:
- Thumb mode.
This is the first architecture to have a full formal definition.
- Ops which yielded PC+12 in earlier ARMs are declared UNPREDICTABLE.
- Reserves some of the SWI space for architecturally-defined operations.