First off, keep in mind that the 64-bit address is the VIRTUAL
address. This is translated to a REAL address by an address
translation unit in the CPU. It is the REAL address space that
determines the maximum amount of storage that can be addressed by
the machine. The actual usable size of the real address space
varies by machine model.
In systems without single-level store each process has its own
address space, and thus the individual process's virtual address
space can be smaller than the real address space or real memory. In
effect, the process ID becomes a part of the virtual address,
effectively increasing the total virtual address space.
In SLS systems, the virtual address space effectively must be large
enough to address all of disk. In this case real memory is really
just cache for the disk space, and so there is no benefit in having
more real memory than there is virtual address space.
Also remember that processors in a multi configuration SHARE real
memory. That is, they both can be addressing the same location at
(almost) the same time. So memory does not have to be logically
divided between processors.
In the newer multi-processor systems, the memory IS physically
divided between processors, but this is something of a
mechanical/electrical convenience, not a logical necessity. The
memory that "belongs" to a given processor can be most efficiently
accessed by that processor, but other processors in the system can
still address the memory with only slightly less efficiency.
Post by Holger SchererMaybe i jumped into this discussion too late,
Do the PowerPCs in our AS/400s do real 64bit addressing
(using the whole 64bit), or how is the addressing done?
i.e. how much storage can one single CPU use
(assuming in a n-way system the maximum of 2^64 exists)?
-h
Post by Dan HicksPost by Dr. Ugo GagliardelliPost by Dan HicksWith newer 64-bit processors, the specialized address translation
hardware isn't so critical. It may improve performance 20% or so,
but isn't a make-or-break thing. It's the tags that can't be easily
duplicated without special hardware.
What's "tags" you're referring to?
The capability tags that allow capabilities to be stored in regular
non-segregated storage without a danger of them being forged.
("Tagged pointers")
--
Dan Hicks
Confusion is a word we have invented for an order which is not
understood. --Henry Miller
--
Dan Hicks
May you live in interesting times. --Ancient Chinese Curse