Windows – How to know when to upgrade RAM in Vista

It's not clear what you're asking. You ask about "total process memory" as if that were a well-defined term. It's really not. The types of memory measurements that seem natural to people who don't have a deep understanding of memory management basically don't exist on modern systems.

A more useful way to do this is for you to tell us what it is you are trying to figure out. We can tell you how to do that. People tend to say things like "I need to know how much memory a process is using", but that's largely meaningless. It's like asking how much space a person is using. Well, they share the bathrooms, should that count? And they have some stuff stored in the garage, but only because nobody is using it and they could throw that stuff away if anyone needed the space, should that count?

There's really no substitute for studying in some level of detail how modern operating systems manage memory, the distinction between physical and virtual memory, clean versus dirty pages, and so on. That way, you can make sense of the numbers the system actually can provide you.

The Performance Monitor (perfmon.exe) has counters for the page file usage.

1. Load it up by either running "perfmon" on a command line, or by selecting "Performance Monitor" under Administrative Tools.
2. Expand "Monitoring Tools" in the left column and select "Performance Monitor."
3. Right-click on the graph to the right and select, "Add Counters."
4. Scroll down the list of available counters to "Paging File."
5. Click on the down-arrow icon to the right of "Paging File."
6. Click on "% Usage" under "Paging File" and then click the "Add" button to put the counter under the "Added counters" list on the right.
7. Click the "OK" button.

The graph will now contain a line for the page file utilization percentage.