Differences between the SMP and BIGSMP Kernels

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Updated: 4 Nov 2008

Updated by: Anders Johansson

Applies to:

  • SUSE Linux Enterprise Server 9
  • SUSE Linux Enterprise Server 10
  • SUSE Linux Enterprise Server 11

A 64 bit system is capable of handling a very large amount of memory, but a 32 bit system is by default only able to handle 4GB. A workaround for this was provided by Intel when they introduced the physical address extension, or pae.

With pae, a 32 bit system is able to handle up to 64GB RAM, in theory. In practice however, the system should not be used with more than 48GB. For more information on the certified amount of memory please have a look at the kernel limits document at http://www.novell.com/products/server/techspecs.html.

The YaST installation system should detect which kernel is the correct one for your system, but in case you add memory after installation, and you exceed 4GB, you should switch from kernel-smp to kernel-bigsmp to enable pae.

In SUSE distributions, pae is only enabled for smp kernels.

Note that in some systems, the BIOS will occupy some part of the memory address space, which means that if you have exactly 4GB RAM in the system, you will have more addressable memory, since you also need to be able to work with the BIOS address ranges, so even if you have 4GB you may still need the bigsmp kernel.

For xen, the pae enabled kernel is simply called kernel-xenpae.

In SLES11 (or in openSUSE versions 11.0 and later), all kernels are smp capable, and the kernel for pae systems is then only called kernel-pae.

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