Can somebody explain this memory usage

[Saaa]

> For one thing, most runtimes will never return memory the the OS so task 
> manager will never show a drop in memory. What you should be looking at is 
> either the resident set size in task manager or some of the GC stats in the 
> process.

What is the resident set size called in winXP taskmanager (Or: which other application should I use to check memory usage)?
How can I chek memory stats? D1-phobos
Thanks