Virtual address space in windows

Virtual address space in windows

All, Forgive me I'm a newbie for the Windows Driver Development, After
read this document from WDK, I have something I didn't understand.
The document says
The range of virtual addresses that is available to a process is called
the virtual address space for the process. Each user-mode process has its
own private virtual address space. For a 32-bit process, the virtual
address space is usually the 2-gigabyte range 0x00000000 through
0x7FFFFFFF. For a 64-bit process, the virtual address space is the
8-terabyte range 0x000'00000000 through 0x7FF'FFFFFFFF. A range of virtual
addresses is sometimes called a range of virtual memory.
My questions about it are :
Supposed there is a computer which has 8-gigabyte memory bank.
Is all the virtual address space actully assigned from this 8-gigabyte
memory?
If one process need to assigned 2g virtual address space, Can I say that
if there are 4 processes running in the system. they totally need
8-gigabyte memory ? If the answer is Yes, Does it means in thes computer
the max number of processes can be ran is 4?
I don't know if I misunderstand something. please correct me. thanks a lot.