Improved system for saving and restoring state in call and return operations

An improved system for saving state during a call operation and restoring state during a return operation in a computer system in which different call and return operations require the saving and restoring of different amounts of state. The components of the system are call instructions whose operation codes specify the amount of state to be saved, frames which contain either basic state saved on every call operation and restored on every return operation or basic state and extended state saved only on certain calls and returns, a frame type item in each frame which specifies whether it contains only basic state or both basic and extended state, a single return instruction, state-saving apparatus which is responsive to the different call instructions, and state-restoring apparatus which is resposive to the single return instruction and to the frame type item. When a call instruction specifies that extended state is to be saved, the state saving apparatus responds thereto by saving both basic and extended state and setting the frame type item to indicate that the frame contains both; when a call instruction indicates that only basic state is to be saved, the state saving apparatus saves only basic state and sets the frame type item accordingly. The state restoration apparatus responds to the return instruction by restoring that state specified by the frame type item.