Are memory-module blanks really important to have for a Dell PowerEdge T110 2 server? Or are they optional

There shouldn't be any measurable performance difference.

The reason that 2x2GB costs more than 4x1GB is that there is an implied value in buying bigger DIMMs, in that you are less likely to have to throw the bigger DIMMs away if/when you go to increase memory again.

If you are using Windows 2000 Server Standard, the maximum addressable memory is 4GB, and there's no way to go beyond that and you might as well just buy the 2x1GB -- leaving the 4x512MB in the server (unless there is a compelling reason to throw it away, in which case you'd buy 4x1GB).

If you have Advanced Server or Enterprise Server, the addressable memory is higher (8GB and 32GB respectively). If you think it possible that you will want to add memory again, then buying the 2x2GB is good value -- especially since you can leave 4x512MB in the board and have 6GB in the server initially.

(PS: Memory limits for 32-bit Windows 2000 versions)

Each App Pool can use up to 2GB of private address space, unless you've played with BCDEDIT options like 3GB.

If all 10 used all 2GB possible, you'd be in paging hell.

Your question is more generally around how processes can allocate memory on Windows - I'll throw some terminology at you for further research.

Private bytes - this is the amount of memory uniquely charged to the process Virtual bytes - this is the total amount of memory the process has allocated Working Set - this is how much RAM is actually being used by the process

Reserved memory - memory that's earmarked for use by an application, but doesn't actually have RAM/pagefile backing yet Committed memory - memory with backing

Now, the question becomes more complicated when you add app frameworks like .Net in - .Net has a lower-than-2GB workable maximum before OutOfMemoryExceptions happen. And generally, in my experience, they won't happen on an application that isn't either leaking something or under greater load than it can handle.

Perfmon with the process counters is typically all you can do with App Pools; you can enable the option to put the PID in the process name, if that helps, and APPCMD LIST WP regularly to keep a note of which app pool is doing what.