Why does the processor not immediately boot into protected or 64-bit mode?

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ural_asadullin2021-04-25 19:02:42

Processors

ural_asadullin, 2021-04-25 19:02:42

Why does the processor not immediately boot into protected or 64-bit mode? And why do we need real mode at all?

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3 answer(s)

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Sergey Karbivnichy, 2021-04-25
@hottabxp

For compatibility with older software.

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rPman, 2021-04-25
@rPman

Why is it not loading directly?
In efi mode, it is just immediately protected and starts

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res2001, 2021-04-26
@res2001

In real mode, everything is somewhat simpler, because. real memory addresses are available. For example, device ports are available at their real addresses. You can quite easily pre-initialize the equipment.
Enabling protected mode implies at least the presence of a software layer that will work with the MMU - allocate / free memory, map real addresses to virtual ones, etc. In addition, the MMU itself is not enabled by default and must be enabled programmatically in real mode. Something like this.