"ray" <ray@xxxxxx> wrote ...
Quote:
> Not a 'dead end' at all - only with MS. Linux 32 bit systems will
> recongize up to 64gb.
By default, most 32-bit Linux kernels address 4GB of memory. You can
configure the Linux kernel to use Intel PAE (Page Address Extensions) to get
36 bit addresses; and hence access up to 64GB of memory. However this extra
memory is not a free gift. Executing code can't run in memory above 4GB,
even when the OS can address that memory. So application code must continue
to live below 4GB. Also, to be directly manipulated by code, data needs to
be moved from the High Zone (> 4GB) back down into the Normal zone, with a
kmap() or similar call. So, even if you have PAE and 64GB memory enabled, it
won't be any use unless your application is PAE-aware. The memory above 4GB
is mainly useful as cache, for example if you have a database application.
Windows Server 2003 offers the same 64GB facility, by booting with with the
"/PAE" switch; and by using AWE memory APIs in your Windows applications (eg
as in 32-bit SQL Server). The limitations of 36-bit addressing on Windows
are similar to those on Linux. The 32-bit Windows Server 2003 Enterprise
edition can address 32 GB of memory (via PAE). In SP1 this was increased to
64GB. Windows automatically enables PAE on CPUs with the DEP feature. Since
most new CPUs are 64-bit anyway, all this memory jiggery-pokery is
fortunately going away ...
--
Andrew McLaren
amclar (at) optusnet dot com dot au