If you're using Task Manager, for example, you will by default only see "Mem Usage" which reports the physical memory (i.e., the "working set") consumed by the process. Even though this metric includes both private and shared pages (i.e., shared code and data segments of DLLs are charged to each process here), it does NOT include pages which still reside on disk (either in the executable images, memory-mapped files, or the system pagefile.
Another common memory statistic from Task Manager is "VM Size" (you have to add it to your column view by "View->Select Columns"). "VM Size" tallies private virtual bytes consumed by the process. Private means that this quantity does NOT include shared/shareable pages like DLLs and memory-mapped files. "VM Size" is sometimes smaller than the "Mem Usage" precisely because shared pages aren't counted. This causes a large amount of consternation to those who don't understand what is being reported, because they expect physical memory usage to be smaller. "VM Size" is the equivalent of the process's page file allocation, since shared pages by their nature are already backed up on disk elsewhere.
Another common memory usage metric in Windows can be obtained from Perfmon (perfmon.msc, the Performance MMC snap-in). From this tool, you can view "Virtual Bytes" of each process, which is the amount of reserved virtual memory for the entire process, including shared pages. It is equivalent to "VM Size" from task manager PLUS shared virtual memory.
So, as you can see, it is not altogether obvious what is being reported unless you really understand the details of memory management on the underlying OS. Before comapring application memory usage across platforms, you need to be sure you're using comparable metrics!
Start Regedit, find HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ Winlogon, Change the value of Shell from Explorer.exe to cmd.exe.
Alternatively, replace it with bbLean.
A newly-installed Windows PC is basically useless. The usual suspects after installation are: