Each of the structures contains three elements, an old value that is held by the corresponding field of the origin object, a new value to be copied to the target object, and a status word that indicates the copying status.
(3) The status and its corresponding field should be simultaneously modified so as to ensure that the status word correctly indicates the latest version of its corresponding field.
The CopyExtendedObject procedure is different from CopyNormalObject; the most essential factor is that the status words are in the "from" object.
There are also the usual control registers (program counter, program status word, system status word) and some internal registers used by the processor.
The mode of the program is determined by a bit in the sytem status word (SSW).
Three additional program addressable registers are provided, the program counter (PC), the program status word (PSW), and the system status word (SSW).
The program status word (PSW) is primarily used to hold status information (condition codes, trap codes) and to set those aspects of the processor state that the user process is permitted to modify, such as floating point trap enables.