[Autogenerated] let's summarize the main concept in the previous two slides we
have the X 86 PT and Pt ES and essentially they have the same layout they
comprise of the bits that point to the physical address,
the beginning of the physical address.
In terms of pages, each entry, 64-bit is eight bytes and by the way,
a page table can also be paged out if needed but the actual entries
they look exactly the same from a conceptual perspective from a layout
perspective in the original kernel of course we only have four bites
one of these entries but we're going to focus on the new scheme that
has eight bytes per entry, the 24 bits.
The upper 24 bits are known as the page frame number.
That's the value.
You have to multiply by the size of a page essentially adding 12 bits
coming from the offset to get to the real addressing physical memory in
the regional kernel it was just 20 bits and because 24 bits required
more space and there are more flags there and intervals already
thinking about 64-bit then they extended that those entries to 64-bit
bit zero is the most important flag there known as the valid bit if
it's one,
it means that the CPU should go ahead and make the translation as we discussed.
If it's not it means there's something wrong with this address,
it's not in physical memory right now as far as the CPU is concerned.
And so a page for it's going to be raised and the CPU is hoping here the
memory manager will do something appropriate notice that page faults can
also happen because of some invited address.
For example, if you think about the page director initially,
it's completely zeroed out, which means that the value it is also zeroed out.
So if you try to access some unavailable address,
which is completely not allocated or committed any kind of way,
then it's also going to raise a page fault.
Exception from the perspective in this case,
the member manager will come to a conclusion that this is just bad
address and will turn the page for the exception access violation and
send that for handling to the original process.
So there are other bits and I'll discuss a few of them later on,
after we look at 64-bit address translation.