UpdateMaker is an application that can determine the differences between any two Macintosh files, be they applications, documents, system files, or whatever. UpdateMaker documents describe the changes needed to convert one file (called the "old" file, whether it is older or not) into the "new" file. You cannot read UpdateMaker documents, since they are stored in a compact form. However, you can apply the UpdateMaker document to a copy of the "old" file and it will generate an exact copy of the "new" file.
Why is this useful? Because UpdateMaker documents can be very much smaller than the files that they apply to, they cost less to send over a computer network or store on a disk. If you wish to send some changes to a large document or a large application to someone who has an older version, sending an UpdateMaker document will cost less than resending the entire document or application. UpdateMaker documents are also more secure in that they can only be used someone who has the "old" file.
Because not everyone who might want to update a file will have a copy of UpdateMaker to apply UpdateMaker documents with, UpdateMaker can also save documents as stand-alone applications. These applications are good for one and only one job – updating the particular file that they were created for. But they can be convenient if you do not know that a copy of UpdateMaker will be available to the receiver of the UpdateMaker document. The stand-alone applications, like UpdateMaker itself , require System 6 or later.
Please note that UpdateMaker documents are inherently reliable. They have internal checksums which will detect damage done to them in transit. They also use checksums to ensure that the target file is identical to the "old" file that the update was built for. Updates are therefore guaranteed to either fail or generate a perfect copy of the "new" file that was used to make them, subject only to any special exceptions specified by the author of the update.
