From mboxrd@z Thu Jan 1 00:00:00 1970 Message-Id: In-Reply-To: <9904021711.AA35268@marc.watson.ibm.com> References: Message from Holger Bettag of "02 Apr 1999 14:11:16 +0200." <8x677fp6hn.fsf@s52.informatik.uni-bremen.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Date: Fri, 2 Apr 1999 17:19:57 -0500 To: linuxppc-dev@lists.linuxppc.org From: Douglas Godfrey Subject: Re: Apple Job Posting and Good News for LinuxPPC developers Sender: owner-linuxppc-dev@lists.linuxppc.org List-Id: Reoly to David Edelsohn, 4/2/99 12:11 PM -0500: Re: Apple Job Posting and Good News for LinuxPPC devel >>>>>> Holger Bettag writes: > >Holger> I have heard rumours that the "Max" core has provisions to >physically address >Holger> more than 4GB of memory (via the MMU's segment registers). >Processes would >Holger> still be limited to a 4GB logical address space, though. > > The PowerPC architecture always has been able to address more than >32-bits of "logical" address space. That is the reason for the PowerPC >terminology of "effective address", "virtual address", and "real address". >The intermediate "virtual address" space of a 32-bit PowerPC >implementation is 52 bits. > > Pointers still are 32-bits, but a cooperating operating system and >compiler can allow an application to address more virtual memory through >runtime modifications to the virtual segments mapped by the segment >registers, like memory overlays. That was the original reason for the >design of the MMU in the POWER (predecessor of PowerPC) architecture. I >do not believe that any compiler / OS combination takes advantage of this >facility. > Only the IBM Mainframe and the AS/400 use windowed virtual storage to access more than 32 bits of address with 32 bit pointers. The IBM Mainframe can access a 44bit address range by using a 32 bit pointer as a base address for a 4k page boundry contiguous storage segment with a window size of up to 16meg. The old AS/400 did something similar to access it's virtual storage mapped database while the new AS/400 just switches to the PPC 64bit addressing mode and uses full 64bit pointers. Thanx... Doug [[ This message was sent via the linuxppc-dev mailing list. Replies are ]] [[ not forced back to the list, so be sure to Cc linuxppc-dev if your ]] [[ reply is of general interest. Please check http://lists.linuxppc.org/ ]] [[ and http://www.linuxppc.org/ for useful information before posting. ]]