A method of installing software on and/or testing software for build-to-order computer system includes reading a plurality of component descriptors from a computer readable file. Each component descriptor describes a respective component of the computer system. A plurality of steps are retrieved from a database, each step being associated with a respective sequence number. The plurality of steps are sequenced in a predetermined order according to the sequence numbers to provide a step sequence. The step sequence includes commands for installing and/or testing software upon the computer system. For each step read from the database, it is determined if that step is incompatible with the presence in the computer system of a component other than that corresponding to the component descriptor associated with the step. If so, the step is discarded or not according to data associated with that step in the database. Also, for each step read from the database it is determined if that step requires a parameter, and if so the parameter is calculated according to data associated with that step in the database.