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X86-64: Difference between revisions
→Are there restrictions on 32-bit code running in Legacy Mode ?: Added a possibility of multiprocessor STARTUP IPI for real mode
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x86-64 processors can operate in a legacy mode, they still start in real mode and protected mode is still available (along with the associated v8086 mode). This means an x86 operating system, even DOS, will still run just fine. The only difference is that physical addresses can be up to 52 bits (or as many bits as implemented by the CPU) when PAE is used.
However, there is nothing like [[Virtual 8086 Mode]] once in long/compatibility mode. <br />
If you are running on a multi-processor system, you could send one processor a STARTUP IPI to a real mode memory address (see Intel MultiProcessor specification for more details) that loads your real mode program. The main problem with this approach is thatt it relies on Multiprocessor.
==Entering Long Mode directly==
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