A register file backup system for use with a computer which processes
instructions to generate results which thereby change the visual state of
the computer. The computer has a register file with a plurality of
addressable locations for storing data. The backup system is adapted to
return the visual state of the computer to a previous state if an
instruction generates an exception. The backup system utilizes less
overhead so as to provide easier register file backup than a comparable
software or hardware device. The backup system comprises first means for
sequentially storing in program order, address information corresponding
to destination locations in the register file where instruction results
are to be stored. The first means has first and second outputs for
transferring the address information stored therein: the first output
being coupled to the register file for transferring a first portion of
the address information to the register file, and the second output is
used for transferring a second portion of address information for backup
storage of the register file contents. The backup system also has a
second means coupled to (1) the second output of the first means, for
receiving and storing the second portion of the address information, and
(2) the register file, for receiving and backup storing further
information corresponding to the contents of one or more destination
locations in the register file before that destination location is
changed according to second portion of the address information. A third
means is used for transferring the further information from the second
means back to the register file locations according to the second portion
of the address information stored in the second means after an
instruction generates an exception.