Windows – Can Task Manager show the total memory usage for a group of processes

what you see in the status bar is the the total commit charge which represents the current amount of virtual memory used.

The "Mem Usage" column in Task Manager's "Processes" display, however, shows each process's current working set. This is a count of physical memory (RAM) rather than virtual address space.

The total commit charge will always be larger than the sum of these values, as the total includes system-wide allocations such as the paged pool.

There is an overlap in memory used by your applications. When an application is using a DLL, which is a shared library, the library is loaded into the physical memory only once, but every application using it sees an increase in its own memory usage. The Wikipedia article on shared libraries explains memory sharing quite well.

I see that your Windows is not in English, but if you try to translate the fields, I hope this information will help (taken from my Windows 7). The resource monitor can display working set, shareable memory and private memory for each process. Shareable memory and private memory are both combined into the working set of the application. Resident set is part of working set which is in physical memory (RAM) as opposed to being swapped on the hard drive.

So each shared library contributes towards the shareable memory of each application, which is a part of the working set. You have added up all working sets of all applications, I believe.