After discussing with Bikram Sir , this what we could conclude -
1) Simultaneous and Hierarchical access is related only when dealing between Cache memory and Main memory, where
a) Write Back meant writing on the cache and only when a block has to be replaced in the cache we write back the contents of that block to the main memory thus making it a Hierarchical access and
b) Write Through meant writing onto the cache and main memory simultaneously whenever the contents are modified making it simultaneous access.
2) When dealing with Primary memory and Secondary Memory , there is no specific thing as simultaneous and hierarchical access.
The general procedure goes this way -
Suppose we want a page called Page X which is not in the Main memory, the following things will happen -
1) Page Table (assuming there is one) will search for Page X and wont find any, this will lead to Page Fault.
2) This will begin the Page Fault Service Time where the it will access the Secondary memory for Page X and once found will load it into the Primary memory and update the page table.
3) Now we will access the Primary memory knowing it is loaded into the Primary memory successfully.
Now , in the above question it was earlier stated that -
" The time required to access page in secondary memory is 100 ns. " , then the Page Fault Service Time would be 100 + 10 = 110 ns.
Now , after being rephrased to -
" The time required to service the page fault is 100 ns. " , then Page Fault Service Time would be 100 ns ( as it includes everything)