We examine the diffusion of a hardware/software system. For such systems there is interdependence between the hardware-adoption decisions of consumers and the supply decisions of software manufacturers. Hence there can be bottlenecks to the diffusion of the system. We consider the CD industry and estimate the (direct) elasticity of adoption with respect to CD player prices and the (cross) elasticity with respect to the variety of CD titles. Our results show that the cross elasticity is significant. Our model can be used to quantify the effect of various policies aimed at speeding up the diffusion of a system.