Is it nessecary to enable the A20 to enter the protected mode? Why enable so much OS the A20?
thx!
Hello!
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mikeleany
RE:Hello!
No, you don't HAVE TO, but you probably WANT TO. First, let me tell you what A20 is. It's line 20 on the address bus (which corresponds with bit 20 of a 32-bit address). If the A20 line is disabled, that means that bit 20 of the address is treated as a 0, even if it's really a 1. So the addresses between 1MB and 2MB are treated as though they were between 0 and 1MB; the addresses between 3MB and 4MB are treated as though they were between 2MB and 3MB; and so on with the rest of the odd megabytes. So basically, if you're going to use any memory above 1MB, then you want to enable the A20 line.