2.2.2. ARM, Thumb, and Thumb-2 instruction sets

The ARM instruction set is a set of 32-bit instructions providing a comprehensive range of operations.

ARMv4T and above define a 16-bit instruction set called the Thumb instruction set. Most of the functionality of the 32-bit ARM instruction set is available, but some operations require more instructions. The Thumb instruction set provides better code density, at the expense of inferior performance.

ARMv6T2 defines Thumb-2, a major enhancement of the Thumb instruction set. Thumb-2 provides almost exactly the same functionality as the ARM instruction set. It has both 16-bit and 32-bit instructions, and achieves ARM-like performance with Thumb-like code density.

ARMv6T2 also defines several new instructions in the ARM instruction set.

In ARMv6 and above, all ARM and Thumb instructions are little-endian. In ARMv6T2 and above, all Thumb-2 instruction fetches are little-endian.

For more information, see Instruction set overview.

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