A method of system design and manufacture includes entering system details in a first user interface program 100, including in particular availability data. A transfer file 110 defining a spreadsheet including cells representing the system is created and transferred to a spreadsheet 120. The spreadsheet calculates both the availability and target availability of the components. The transfer file is arranged to define component count spreadsheet cells to permit user input to vary the numbers of at least some components of the system, and calculation cells to calculate the properties of the system for the component counts entered into the component count cells. The user can then adjust the spreadsheet to obtain a desired result, output the final configuration as output file 130 and pass the file to a manufacturing facility 140 to produce the designed system. The system designed and manufactured may be a computer system with many components.