Is this DLL temporary unloading or paging or ???

I often run 20 or 30 programs at the same time
I have enough physical memory to do this without paging

I also leave my machine on 24x7 as it receives data from customers'
servers every 5 minutes

When I start work again in the morning each program I use takes a long
time to respond

There is hard disk activity for a while - and once finished the
program carries on just fine

But it can take up to 2 minutes per program and with 30 programs that
is up to 60 minutes of waiting in total

I am trying to guess what windows is doing to my processes:

1) unloading dlls - that are then reloaded when I start using the
program again and they are called into
2) paging code to disk
3) paging dlls to disk - I read somewhere that windows never does
this?
4) paging the heap to disk

Does anybody have an idea?
And if so give any pointers as to how to stop it?