What is the swap space in the disk used for?

Suppose n processes, P₁,......., P_n share m identical resource units, which can be reserved and released one at a time. The maximum resource requirement of process P_i is S_i, where S_i > 0. Which one of the following is a sufficient condition for ensuring that deadlock does not occur?

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 it's 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:

Normally user programs are prevented from handling $${\rm I}/O$$ directly by $${\rm I}/O$$ instructions in the for $$CPU$$ having explicit $${\rm I}/O$$ instructions, such $${\rm I}/O$$ protection is ensured by having the $${\rm I}/O$$ instructions privilege in $$CPU$$ with memory mapped $${\rm I}/O$$ there is no explicit $${\rm I}/O$$ instruction. Which one of the following is true for a $$CPU$$ with memory mapped $${\rm I}/O$$?