'Manufacturing in the Computer' denotes the virtual manufacturing vision that fabrication/assembly of any product can be simulated in a computer by a powerful modeling and simulation environment. This paper presents the DDM approach, documentation-driven manufacturing to address the problem of engineering such an environment. The key to DDM is the creation and application of the engineering repository (ER) that supports multiple views for modeling and simulating virtual production in the computer and model control of physical production in the factory, respectively. Both virtual view and physical view are heeded for manufacturing under the support of the ER. The ER tangibly documents virtual parts and make them well organized for use by 'iteration-to-maturity' in the computer. It also provides a means for driving the virtual production from one stage to another throughout the manufacturing process, and for converting documents between virtual view and physical view representation to manage and control the physical production.