The "Memory (Private Working Set)" column in Task Manager isn't a particularly useful counter to look at if you're interested in the true physical memory demands of processes because it only represents the private pages which are currently in the working set and does not include shareable pages nor how much of a processes private data isn't in the working set but is still in physical memory occupying space i.e. on the modified page list. You can configure Task Manager to display the total working set of processes (private plus shareable pages) by adding the "Memory - Working Set" column by going to "View" in the menu bar and then selecting "Select columns...". Alternatively, you could use
Process Explorer to show this information.
As far as how to see how much of a processes private pages of memory isn't in it's working set but is still occupying space in physical memory sitting on the modified page list. Task Manager, or any other tool in Windows, wont show you this sort of information and you will need to download a program called
RAMMap to see the breakdown. Once you have downloaded RAMMap and you have it running, if you navigate to the "Processes" tab, you will be able to see how much of a processes private data is in the working set but is also sitting on the modified as well as the standby page list. You can also see the breakdown of physical memory by type of memory for the paging lists (Standby, Modified, Modified-No-Write, Zeroed, Free and Bad) as well as what's active by navigating to the "Use Counts" tab in RAMMap
If you're looking to diagnose a problem or are just interested in the state of the system, Task Manager isn't particularly a great tool to use because it's rather inconsistent and isn't entirely accurate when it comes too its labelling scheme. The most insidious one is the "Page File" counter in the Windows XP and Windows Vista Task Manager. Even if the system has been configured to run without a pagefile, that page file counter would still display a non-zero value because it doesn't represent page file usage, it is displaying the amount of committed virtual memory processes have allocated which is backed by physical memory or the paging file(s), i.e. system commit.
So, in conclusion, don't use Task Manager.