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SubjectRe: x86 question: Can a process have > 3GB memory?
Date
Robert Love writes:
> On Thu, 2002-05-09 at 14:24, tchiwam wrote:

>> How about other architectures ? like PowerPc.
>> Last calculation I did used 11GB of ram (no swap) on a big Number
>> Muncher... Would it be nice to use the same code for testing on 32
>> architectures with swap ?
>
> All 32-bit architectures have a 4GB address space, 64-bit architectures
> obviously have a much bigger one (depends on the arch how many bits are
> used for the address space).
>
> PPC obviously does not have the dumb physical memory limitations x86
> has, however.

Huh? Unless you mean ppc64, ppc is worse.
On a Mac, you get 2 GB of virtual memory per
process. You get up to 512 MB of physical memory
without highmem support, or usually 4 GB with
highmem support. As with x86, the latest chips
offer a 36-bit (64 GB) physical address space.

Virtual memory layout:

00000000-7fffffff user
80000000-bfffffff waste (for IO on obscure Amiga "upgrade" junk)
c0000000-dfffffff non-paged mapping of 512 MB at phys addr 0
e0000000-ffffffff IO, vmalloc(), etc.

That's not all! Linus recently singled out the PowerPC
MMU for a nice long abusive rant. :-) You get hashed
page tables. You get this:

As with x86, segment registers map a 32-bit virtual
address space onto a larger one. The top 4 bits of
a 32-bit virtual address are used to select a segment,
and the segment provides 24 more address bits to
give you a 52-bit virtual address. Eeeew.
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