What is different between "pager" and "Lazy swapper"?

Question

I'm reading a book, operating system concepts (written by abraham silberschatz), in chapter 9 virtual memory, there are terms Lazy swapper and pager.

I can't figure out what is different between Lazy swapper and pager.

Swapper is just doing the entire process into memory, whereas lazy swapper is doing swapping a page rather than entire process.

Is it pager?

Solution 1

A demand paging system is quite similar to a paging system with swapping. When we want to execute a process, we swap it into memory. Rather than swapping the entire process into memory, however, we use a lazy swapper called pager. But both do it in a different way. Swapper Copies all pages related to a whole process(used in earlier days). But Lazy swapper do it Page-by-Page, That's why it is lazy... jokes apart

Solution 2

Lazy swapper is the same as pager.. Swapper isn't the same as Lazy Swapper
To be more specific they do the same thing as the two moves data from memory to a place on the Hard Disk called BackStore, but each do it in a different way. Swapper was used in the early days to copy entire process out of memory if no enough memory was available. Pager copies a victimized page contents on the paging device - page by page. or pooling device then to hte paging device. if no pages are available.

Hope that helps.. :)

Solution 3

Quote from the book in the question(Chapter 9, p. 401):

A lazy swapper never swaps a page into memory unless that page will be needed. In the context of a demand-paging system, use of the term swapper is technically incorrect. A swapper manipulates entire processes, whereas a pager is concerned with the individual pages of a process.We thus use pager, rather than swapper, in connection with demand paging.