Let’s discuss the processor modes. The ARM7 core has seven operating modes. The user mode is an unprivileged mode under which most applications run. The system mode is a privileged mode that uses the same registers as the user mode. The user mode and system mode are the only modes that are not involved with exceptions or interrupts. The remaining modes are involved with exceptions and interrupt handling. The first of those is the FIQ, or fast interrupt paneling, high priority processor mode. The IRQ is the general purpose paneling mode. Supervisor is a protected mode for the operating system which is entered on reset or when an SWI instruction has been received. The abort mode handles memory access violations and the undefined mode handles undefined instructions within the core. As you can see here, all of the modes, except for user mode, are privileged. In addition, all of the modes except for user and system are involved with exception modes. Typically, when your code is operating in a normal program, it will be operating in either user or system mode depending on how you've chosen to architect your application.