Apple Job Posting and Good News for LinuxPPC developers
hobold at Informatik.Uni-Bremen.DE
Sun Apr 4 03:42:53 EST 1999
David Edelsohn <dje at watson.ibm.com> writes:
> >>>>> Holger Bettag writes:
> Holger> I have heard rumours that the "Max" core has provisions to
> Holger> physically address more than 4GB of memory (via the MMU's segment
> Holger> registers). Processes would still be limited to a 4GB logical
> Holger> 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.
OK, that's true in the usual PowerPC terminology.
> Pointers still are 32-bits, but a cooperating operating system and
That's what I meant with processes being limited to a 4GB logical address
space, because the segment registers are not accessible with only user mode
> 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
Well, so far there are no 32bit PowerPCs that can handle more than 4GB of
RAM. The rumours I heard indicate that "Max" might be able to handle more.
That would make messing with segments worth the effort (and would generate
all the neat problems of segmented addressing schemes).
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