You're right in saying that physical addresses are sequential. On an offtopic note, there are patches which allow non-sequential physical memory regions: badram and NUMA.
I've written: "The 3 GB addressable RAM available to each process is mapped to the available physical RAM."
This means that the userspace application can grow to a maximum of 3 GB. It is not necessary to have 3 GB of physical memory to map it all. The kernel "swaps out" some of the physical pages to make room for processes that might need more RAM. If a process accesses a page that has been swapped out, it is brought back in RAM (possibly after swapping out some other page).
This is a wonderful concept, take a look at some OS theory or i386 manuals for the complete description.
Re: I have trouble understanding...
You're right in saying that physical addresses are sequential. On an offtopic note, there are patches which allow non-sequential physical memory regions: badram and NUMA.
I've written: "The 3 GB addressable RAM available to each process is mapped to the available physical RAM."
This means that the userspace application can grow to a maximum of 3 GB. It is not necessary to have 3 GB of physical memory to map it all. The kernel "swaps out" some of the physical pages to make room for processes that might need more RAM. If a process accesses a page that has been swapped out, it is brought back in RAM (possibly after swapping out some other page).
This is a wonderful concept, take a look at some OS theory or i386 manuals for the complete description.
--
Amit Shah
http://amitshah.nav.to/