Max RAM Supported

Paul Mackerras paulus at
Wed Oct 20 22:21:03 EST 2004

Amit K Tiwari writes:

> I have just installed YDL 4.0. The OS does not show all 6GB DRAM I
> have in my Power Mac G5. It shows only 1.97GB (I ran top to see how
> much physical memory I have). Looking at the net,

Is that a 32-bit kernel or a 64-bit kernel?  (If uname -m prints ppc,
it's a 32-bit kernel; if it prints ppc64, it's a 64-bit kernel.)

The 32-bit kernel only supports 2GB of RAM, because it can only use
physical addresses below 4GB, and the space from 2GB - 4GB in the
physical address space is used for I/O and ROM.  The 64-bit kernel can
address all of the physical address space.

> Do I need to re-build the kernel to enable the support for all of
> available memory? If yes, with what options? 'High Memory Support' is
> already enabled in the kernel config.

You need to build a 64-bit kernel (i.e. ARCH=ppc64) rather than a
32-bit kernel (ARCH=ppc).


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