Q70

Consider a disk drive with the following specifications: $16$ surfaces, $512$ tracks/surface, $512$ sectors/track, $1$ KB/sector, rotation speed $3000$ rpm. The disk is operated in cycle stealing mode whereby whenever one $4$ byte word is ready it is sent to memory; similarly, for writing, the disk interface reads a $4$ byte word from the memory in each DMA cycle. Memory cycle time is $40$ nsec. The maximum percentage of time that the CPU gets blocked during DMA operation is: