As we mentioned earlier, the Thumb instruction set’s primary purpose is to allow for smaller code sizes – so the user can get by with less memory. However, due to the 16-bit nature of these instructions, there is a speed penalty incurred by using this mode causing longer code execution times. The primary reason for the speed penalty is the time it takes to decompress to a full 32-bit size before execution – since the core always executes in 32-bits.