3GB Thread limit

bscott@ntisys.com bscott at ntisys.com
Thu Nov 21 07:38:00 CST 2002


On Wed, 20 Nov 2002, at 9:29am, a.salomon at sympatico.ca wrote:
> Any ideas how to get around the 3GB per thread limit ...

  Buy an Alpha and run Linux on it.  Seriously.  (Sorry, Dell.)

  It is not a Linux limit, it is a 32-bit limit.  32 bits of address space
means the processor can address a maximum of 2^32 = 4294967296 bytes of
memory -- exactly 4 gigabytes.  The kernel and the hardware has to have some
of that, leaving you with roughly 3.5 gigabytes available for user
processes.

  The 64-bit Alpha can address up to 18446744073709551616 bytes of memory.

> Seems a waste if I have 8GB ...

  The kernel can use special hardware support that lets it manage more than
4 GB of memory, but only 4 GB will be available to a single process at a
single time.  It is almost as if the memory above 4 GB becomes a really fast
swap disk.  Significantly better than nothing, but far from 64-bit native
support.

-- 
Ben Scott <bscott at ntisys.com>
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