Why are 32-bit application pools more efficient in IIS? [closed]

Solution 1:

64-bit memory pointers and other related data structures are twice as large as their 32-bit counterparts. In addition, a 64-bit worker thread will incur a penalty every time it has to access 32-bit code or DLLs as it switches modes. (Research WoW64 and thunking.)

The biggest (but not the only) advantage of using 64 bits is the ability to address much more memory. If your app pool doesn't use more than 2 or 3 gigabytes of memory, and you don't specifically need to run 64-bit code, then there probably is not a compelling reason for you to go 64-bit. As technology advances, chip makers are making additional CPU registers especially for 64-bit processors to improve their performance, but generally speaking, there's no magical performance boost just for using more bits. In fact, as you've just witnessed, it can be worse.

64-bit = Abrams Tank

32-bit = Toyota Prius

One can get a lot more work done, but the other can fit through the McDonald's drive-through.