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Thumb is a 16-bit instruction set for ARM processors. While incorporating the same design characteristics, the Thumb instruction set requires only a 16-bit wide system data bus, thereby using less power, offering a smaller footprint, and reducing overall system cost. The Thumb instruction set features a subset of the most commonly used 32-bit ARM instructions, which have been compressed into 16-bit wide codes to provide better code densities. On execution, these 16-bit instructions are decompressed transparently and in real-time to full 32-bit instructions.

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ARM