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HIGHMEM64G support was added in linux-2.3.25 to support (then) high-end Pentium Pro and Pentium III Xeon servers with more than 4GB of addressing, NUMA and PCI-X slots started appearing. I have found no evidence of this ever being used in regular dual-socket servers or consumer devices, all the users seem obsolete these days, even by i386 standards: - Support for NUMA servers (NUMA-Q, IBM x440, unisys) was already removed ten years ago. - 4+ socket non-NUMA servers based on Intel 450GX/450NX, HP F8 and ServerWorks ServerSet/GrandChampion could theoretically still work with 8GB, but these were exceptionally rare even 20 years ago and would have usually been equipped with than the maximum amount of RAM. - Some SKUs of the Celeron D from 2004 had 64-bit mode fused off but could still work in a Socket 775 mainboard designed for the later Core 2 Duo and 8GB. Apparently most BIOSes at the time only allowed 64-bit CPUs. - The rare Xeon LV "Sossaman" came on a few motherboards with registered DDR2 memory support up to 16GB. - In the early days of x86-64 hardware, there was sometimes the need to run a 32-bit kernel to work around bugs in the hardware drivers, or in the syscall emulation for 32-bit userspace. This likely still works but there should never be a need for this any more. PAE mode is still required to get access to the 'NX' bit on Atom 'Pentium M' and 'Core Duo' CPUs. Signed-off-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: https://lore.kernel.org/r/20250226213714.4040853-6-arnd@kernel.org |
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| .. | ||
| i386 | ||
| x86_64 | ||
| amd_hsmp.rst | ||
| amd-memory-encryption.rst | ||
| boot.rst | ||
| booting-dt.rst | ||
| buslock.rst | ||
| cpuinfo.rst | ||
| earlyprintk.rst | ||
| elf_auxvec.rst | ||
| entry_64.rst | ||
| exception-tables.rst | ||
| features.rst | ||
| ifs.rst | ||
| index.rst | ||
| intel_txt.rst | ||
| intel-hfi.rst | ||
| iommu.rst | ||
| kernel-stacks.rst | ||
| mds.rst | ||
| microcode.rst | ||
| mtrr.rst | ||
| orc-unwinder.rst | ||
| pat.rst | ||
| pti.rst | ||
| resctrl.rst | ||
| sgx.rst | ||
| shstk.rst | ||
| sva.rst | ||
| tdx.rst | ||
| tlb.rst | ||
| topology.rst | ||
| tsx_async_abort.rst | ||
| usb-legacy-support.rst | ||
| xstate.rst | ||
| zero-page.rst | ||