There was no registry entry for that, but there was/is an entry for the paging executive (DisablePagingExecutive) that keeps driver
code and kernel system code (that would normally be in kernel paged pool) from being pageable to disk. This is an on or off setting, though, it doesn't then page these to disk later if the system is busy.
Steve's right though, you should probably let the OS handle paging activity. However, with 8GB of RAM, you might instead want to consider setting the paging file to something like 512MB, and then do some testing
to see if you really need a paging file at all.