memory - When does Windows decide to pull out pages from Working Set?

I am looking at the distribution of physical memory using the RAMMap tool by SysInternals. The distribution (see image below) shows

1. 1.7 GB in Free (Zeroed) memory list


2. 1.2 GB in Working Set list


3. 550 MB in Standby list



4. 125 MB in Modified list

   
   
   
   

   

I understand that when a process requires memory, Windows searches for memory in the lists in the order Free (Zeroed) -> Standby -> Modified. Hence, as long as we have Free page frames, everything should either be in the Working Set list or Free list.

1. Is this assumption right?


2. If so, why do we see 125 MB of pages in the Modified list?


3. In general, when does Windows decide to pull out pages from Working set list to Modified/Standby list even when there is Free memory left?

I am using Windows 7, with 4.0 GB of installed RAM, 3.5 GB being usable.