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I don't understand why we must activate A20 line before switch to protected mode. Actually i don't make this and my program work fine.
With A0 to A19 address line we can acces from 0 to FFFFF memory (1Mo).
With A20 activated, we can acces from 0 to 1FFFFF memory (2Mo).
In protected mode adresse are coded on 32 bits, from 0 to FFFFFFFF (4Go).
What's the role of A20 line here ? To acces to memory from 1 to 2Mo if i return to real mode ?
It's mainly a compatibility thing. On some machines you will find that if A20 is not activated, you will only be able to access every other MiB of address space in PMode. It may be that emulators/modern PC's don't do this - but better to be safe.
"Certainly avoid yourself. He is a newbie and might not realize it. You'll hate his code deeply a few years down the road." - Sortie
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