Clarification about MemToLeave on 64-bit SQL Server

Hi all,

I am reading a book about SQL Server that states:

"The size of the Virtual Address Space on a 64-bit server guarantees that even after the

buffer pool memory has been allocated by SQL Server, there will still be sufficient user

mode VAS available to handle non-buffer pool memory requests".

My question is that if the system has only 4GB physical memory installed, how being 64-bit will guaranty enough space for non-buffer pool memory? What if BP consumes as much as it can and no space be left for non-buffer pool? Why -g startup parameter does not apply for 64-bit system?

Thanks in advance,

Leila