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VirtualBox and RAM

rakslice edited this page Feb 9, 2023 · 10 revisions

VirtualBox and RAM (or: getting more than 16mb in AIX on non-PS/2 machines)

In a default AIX PS/2 config in VirtualBox you get ~3300 pages (13.5 MB).

AIX PS/2 appears to require the interrupt 0x15 ah=0xc7 memory map API, which has very little support outside of IBM PS/2 machines, and without it is limited to <16MB.

It's actually the bootloader that's responsible for calling this and passing the resulting memory map in to the kernel -- as evidenced by the presence of the corresponding struct in the AIX headers with a description of this in the comments.

Patching the bootloader to not do this and instead give a canned map -- with amounts that also agree with the information available through other supported BIOS calls -- causes it to make available the full RAM of the VM. But see the instructions in the PTF0024 U436295 release notes for changing the kernel address range to avoid corruption with memory amounts over 80mb.

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