1. A host controller comprising: a descriptor fetch unit adapted to send out requests for descriptors and receive descriptors in reply to said requests, said descriptors being data structures for describing attributes of the data transfer to and from devices controlled by said host controller; and a descriptor cache adapted to store prefetched descriptors, wherein said descriptor cache is further adapted to store individual replacement control values for at least a part of the stored prefetched descriptors, and wherein the host controller is arranged to replace a stored prefetched descriptor in said descriptor cache by a newly prefetched descriptor based on the replacement control value associated with the stored prefetched descriptor.