Question

Normal memory access to RAM takes several nanoseconds. But if the target of the request is on a page not now in memory, this can take, e.g., up to 100 ms. Your boss says that it can actually take over 200 ms (i.e., twice as long) in some cases. Is he right? Why or why not?

Answer 1

Yes, he is right. It might happens in some cases.

Suppose if some page is not in memeory we have to go to secondary memory and we will fetch the page from secondary memory. Suppose if the main memory is full we have to replace someframe in main memory and we have to replace it with the new page in that frame.

There is one concept called dirty paging i.e if some page in main memory has to be replaced by another page the and if the existed page is modifed in the main memory, before replacement of the page it has to write back it's contents to the disk which is nothing but secondary memory.

So, totally we require two secondary memory accesses.

One access for write back the existed dirty page contents to the secondary memory.

One access for bring back the requested page.

Note:If some page is modified in the main memory it is called as dirty page.