Dynamic Linking RAM usage?

On windows, dynamic linking is typically done with dll files. When the os loads a program into RAM, it loads a copy of each dll the program uses, right? When two programs use the same dll, do they both get a separate copy of the dll? I don't know why, but I was thinking about it, and it seems like it'd be a huge memory waster if each program had copies of the same libraries loading into RAM simultaneously. Do modern operating systems like windows
take care of this, or do they really waste that much memory? It seems like they could make the os set up an area of RAM for this purpose when the os boots up, right?
Meh.
/Discuss

It's not really a waste.

You know that every program on a protected mode x86 operating system can access 4gigs of memory, so the amount of memory that windows will have to reserve in it's page file or in ram is the same with or without dlls loaded. Of course not all of this memory has to be allocated when the program starts, but chances are very high that a program that runs on windows will need to access it's api's and that's why they load them anyway.

That's exactly how a page file works and it wouldn't working on a system with very limited resources, but then windows wouldn't run there either. Such a system would run on either a custom operating system (graphical calculators for example) which don't even need to support multitasking and a virtual address space, or a modified linux distro which doesn't use page files (those used by digital forensics so that they don't destroy any evidence on the suspects' computer)

Windows loads only two dll's into a programs memory when it starts: kernel32.dll and ntdll.dll. They are needed during PE program startup and the first code executed in a new program is located in ntdll.dll!ldrloaddll(). All other dll's your program loads itself. Now apart form the fact that windows does not know how much memory it has to reserve for a program beforehand, and that programs are likely to need the windows api. There are also security reasons involved, if I changed code in the library then all other applications would have the same change, this leaves an enormous security gap. Read-only memory is not really an option, since large portions of memory would be blocked for the application eg. Even if I don't have any libraries loaded at 0x5000000 I still could not use this memory because a shared library is located here (even if it isn't loaded right now)

In windows Kernel memory is shared, so it's not that inefficient.