5 Related Work 6 Conclusions and Future Work 4 Implementation

with a picture group pattern of IBBPBBPBBPBB. (MPEG encodings contain three types of frames, I, P, and B, that vary in size and importance.) The pattern 100000000000 requests that only the I-frames be prefetched. The pattern 100100100100 requests both Iframes and P-frames. Patterns can be of arbitrary length. For example, 100100100100100100100000 requests all Iframes and five of every six P-frames. Finally the fifth argument to pf_start is the rate at which the frames will be accessed. This is in frames per second with a negative number indicating that the frames will be read in a backwards direction. If a feasible prefetching plan can be constructed then pf_start sets it into action and returns a descriptor. The application uses the descriptor to refer to the plan in the future to modify or stop it. It is possible to initiate several prefetching sequences for the same file. pf_start fails and returns zero if the prefetcher determines that given available resources there is not a feasible prefetching plan that will satisfy the request. pf_modify() changes an executing prefetching plan. This might be used, for example, when a user pushes the fast-forward button in a VCR application. The frame argument is taken to indicate the application’s current position in accessing the data file and the revised prefetching plan will begin from that point. Pattern and rate have the same meaning as for the pf_start call. pf_stop terminates the execution of a prefetching plan.