Overhead of I/O Using DMA Assume initial setup of DMA transfer takes 1000 cycles, handling of interrupt at DMA completion takes 500 cycles, average transfer from disk is 8KB Each DMA transfer takes 8KB/(4MB/s) = 2x10^-3s If the disk is constantly transferring data, it requires: (1000+500)/(2x10^-3) = 750x10^3 cycles Fraction of CPU time= 750x10^3/(500x10^6) = 0.15%
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