Microsoft added to Windows 11 support for Intel’s Advanced Performance Extensions (APX).. The news emerged in Insider build 29695, belonging to the “Rubidium” branch, and it was Xeno, an X user and Windows enthusiast, who noticed it. In the settings there is a switch with the description “Allow Windows to use APX for better performance“. Activating it requires a reboot.
Currently no consumer PC is capable of taking advantage of APX. The extension is expected to debut with i Intel “Nova Lake” processors in early 2027but software development proceeds in advance to ensure the ecosystem is ready for the arrival of the hardware. Microsoft’s work on the Rubidium branch, which could merge into Windows 11 27H2, indicates that the times for general users will not be short.
APX is an extension of the x86-64 ISA introduced by Intel in July 2023 for improve 64-bit performance and efficiency. In August this year the company released version 9 of the specification and has already enabled the entire feature set in GCC 15, so that developers can take advantage of it on compatible hardware.
The main change is the doubling of general purpose registers (GPR) from 16 to 32. With more registers available, the processor can hold in this more data without repeatedly accessing the memory. Intel estimates, in simulations based on the SPEC CPU 2017 Integer suite, that code compiled for APX may have approximately 10% fewer loads, over 20% fewer stores and 10% fewer instructionsdespite the increased length of the new instructions. They should therefore result fewer CPU cycles to complete the same job and more free resources for other tasks.
APX it also introduces three-operand instructions with a new data destination register (NDD), which allow operations to use a separate destination register and reduce unnecessary register transfers. New conditional load, store, and compare statements help compilers reduce branches, while the new No Flags (NF) feature helps avoid unnecessary status flag updates.
These improvements were introduced to help avoid performance penalties due to branch prediction errors. Finally, PUSH2/POP2 instructions improve register saving and restoring efficiency, while a new 64-bit absolute direct jump instruction expands the instruction set.
