Light from a helium-neon laser (wavelength 633 nm) passes through a 0.5 mm diameter hole. how far away should a viewing screen be placed to observe a diffraction pattern whose central maximum is 3.0 mm in diameter ?

Consider a file currently consisting of 200 blocks. assume that the file control block (and the index block in the case of indexed allocation) is already in memory. calculate how many disk i/o operations are required for contiguous, linked, and indexed (single-level) allocation strategies, for each of the conditions listed below. in the contiguous-allocation case, assume that there is not room to grow at the beginning but there is room to grow at the end. also assume that the block information to be added is stored in memory.