In an example implementation according to aspects of the present disclosure, a system comprising a memory and a controller coupled to the memory. The controller receives a transitionary firmware package. The controller extracts a transitionary firmware from the transitionary firmware package. The controller writes the transitionary firmware to memory, wherein the transitionary firmware comprises a reduced functionality for each of a set of central processing units. The controller identifies the CPU currently installed in the system and determines a full featured firmware corresponding to that CPU. The controller writes the full featured firmware to the memory.