Process Explorer is a system resources monitoring tool for Windows operating systems. It follows the general lead of the built-in Windows Task Manager tool, but extends the feature set greatly. These expanded features allow profiling and modification of the real-time state of the system and grants access to otherwise inaccessible or hard to come by information such as showing which thread within a process is running, global searches for file and other open handles, parent-child relationships among processes, and other process-level minutia.
The Process Explorer display consists of two sub-windows. The top window always shows a list of the currently active processes, including the names of their owning accounts, whereas the information displayed in the bottom window depends on the mode that Process Explorer is in: if it is in handle mode you'll see the handles that the process selected in the top window has opened; if Process Explorer is in DLL mode you'll see the DLLs and memory-mapped files that the process has loaded. Process Explorer also has a powerful search capability that will quickly show you which processes have particular handles opened or DLLs loaded.