Consider the following justifications for commonly using the two-level $CPU$ scheduling:
I. It is used when memory is too small to hold all the ready processes.
II. Because its performance is same as that of the $FIFO$.
III. Because it facilitates putting some set of processes into memory and a choice is made from that.
IV. Because it does not allow to adjust the set of in-core processes.
Which of the following is true ?
- $I, III$ and $IV$
- $I$ and $II$
- $III$ and $IV$
- $I$ and $III$