A method of manufacturing a build-to-order PC system unit having at least one hardware component, e.g. motherboard, bearing a unique identifier ("component ID") in software readable form. The method comprises generating a digital identifier ("system trackcode") which defines the hardware and software configuration of the item, storing the system trackcode in association with the component ID in a manufacturing database such that the component ID can be used as a key to retrieve the associated system trackcode. During manufacture the component ID is read from the motherboard and used to retrieve the associated system trackcode from the database.