What is the maximum memory supported by RHEL/CentOS 5 32-bit?
Question:
What is the maximum memory supported by RHEL/CentOS 5 32-bit?
Answer:
The 32-bit PAE kernel supports a maximum of 64GB.
However, running a 32-bit kernel with this much memory is not recommended. On 32-bit systems, the memory is divided into 3 zones:
- DMA = 0-16MB
- Normal = 16MB-1GB
- High = 16GB
The kernel is restricted to allocating it's data structures in the Normal zone. This includes data structures used to manage the High memory zone. The more memory in the system, the more of the Normal zone must be dedicated to managing it. For example:
16GB = LowTotal/LowFree 773704 kB/730096 kB 32GB = LowTotal/LowFree 642632 kB/599524 kB 64GB = LowTotal/LowFree 387656 kB/341396 kB
This is why Redhat only officially supports 16GB in the 32-bit version:
http://www.redhat.com/rhel/compare/
32GB should also work, but anything above that and the system will probably have problems running out of low memory.