ARM stands for Advanced RISC machine. ARM7 belongs to the ARM family of 32 bit core processors.ARM7TDMI is the most used RISC core from ARM.It has 32 bit address bus and 7 operating modes. Each of the operating modes can be used one at a time and they all perform some specific dedicated functions. The 7 operating modes of ARM7TDMI are :

1. User - A non-privileged operating mode,it is the usual ARM program execution state and is used for executing most application programs(tasks).In this mode,programs cannot access some system resources for security reasons. (Privilege is the ability to perform tasks like accessing resources or changing the mode).
2. Fast Interrupt (FIQ) - This is a privileged operating mode and is used to handle a high priority/fast interrupt.
3. Interrupt (IRQ) - It is a privileged operating mode. Used for general purpose interrupt handling.
4. Supervisor - It is protected mode of the operating system. It is also a privileged mode.
5. Abort - This mode comes into picture after a data or instruction prefetch abort.It is a privileged mode that implements memory protection.
6. Undefined - This mode supports software emulation of hardware coprocessors.
7. System - It runs privileged operating systems tasks. This mode is not entered by any exception and has same registers set as User mode.It is also a privileged mode of operation.