I cannot find these numbers anywhere on the IBM Web site or even random blogs that Google finds.


  • What is the maximum physical memory size a POWER7 CPU supports?
  • What is the maximum physical memory size AIX 7.1 supports?
  • What is the virtual address space (per process) in AIX?

Memory requirements AIX Version 7.1 minimum and maximum current memory requirements vary, based on the configuration.

A general rule for a minimum current memory requirement for AIX 7.1 is 512 MB. A smaller minimum current memory may support a configuration with a very small number of devices or a small maximum memory configuration.

AIX 7.1 requires the minimum current memory requirement to increase as the maximum memory configuration or the number of devices scales upward, or both. Larger maximum memory configurations or additional devices scale up the minimum current memory requirement. If the minimum memory requirement is not increased along with the maximum memory configuration, the partition hangs during the initial program load (IPL).

The total virtual address space of a process depends on whether the process is 32-bit or 64-bit. While the total virtual memory on the system is the sum of physical memory plus swap.

The 32-bit AIX Virtual Memory Model AIX assigns a virtual address space partitioned into 16 segments of 256 MB.

Processing address space to data is managed at the segment level, so a data segment can either be shared (between processes), or private.

Segment 0 is assigned to the kernel. Segment 1 is application program text (static native code). Segment 2 is the application program data and application stack (primordial thread stack and private data). Segments 3 to C are shared memory available to all processes. Segment D is the shared library text. Segment E is also shared memory and miscellaneous kernel usage. Segment F is the data area.

The 64-bit AIX Virtual Memory Model The 64-bit model allows many more segments, although each segment is still 256 MB.

Again, the address space is managed at segment level, but the granularity of function for each segment is much finer.

With the large address space available to the 64-bit process, you are unlikely to encounter the same kind of problems with relation to native heap, although you might still suffer from a leak in the native heap.


Can only answer the third question partly, although there is no current documentation on this topic since the switch to 64 bit kernels that I'm aware of. See Inter-Process Communication (IPC) Limits in the Programming section of the AIX 5.3 documentation. You may find something more current in the PDFs in the section Programming for AIX under AIX PDFs, especially in "General programming concepts"

For the second question, you might find some pointers in the Redbook IBM AIX Version 7.1 Differences Guide especially in section 1.2 Improved performance using 1 TB segments

I'll try to get some definitive information on the first and second question. For the first question, the maximum physical memory configuration for the biggest Power7 system (p795) is 16TB, and in addition you could enable AME (active memory expansion)


For the second question, there is no maximum size, all the relevant registers have been beefed up in the past. And there's also no technical limitation why one partition could not allocate all the available memory in a physical system.

For the first question, did not find anything definitive on POWER7. For POWER8, each socket is connected to 8 Centaur chips, with 128GB RAM modules this setup currently supports up to 1TB per socket and there are systems announced with 12 sockets, and maybe even larger memory cards. Although that does not necessarily mean this is the upper limit, just that nothing above that has officially been announced yet.

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