Abstract: A method and system for downloading software update data for installing a revised software product on a client computer minimizes the amount of update data to be transmitted over the network by downloading only those files needed to put the client computer in the state for installing the product. In the beginning of the downloading process, the client computer obtains from a setup server an initial setup package that includes a setup program and a list of files required for installing the software product. The setup program running on the client computer then determines whether some current or earlier versions of those files required for installation already exist on the client computer, and compiles a request list of files needed for updating the client computer. The client computer sends the request list to a download server, which maintains a collection of update files and patches. In response to the request list, the download server downloads updating files to the client.