diff options
| -rw-r--r-- | bootasm.S | 10 |
1 files changed, 3 insertions, 7 deletions
@@ -33,13 +33,9 @@ start: movw $start,%sp # Stack Pointer # Enable A20: - # For fascinating historical reasons (related to the fact that - # the earliest 8086-based PCs could only address 1MB of physical - # memory and subsequent 80286-based PCs wanted to retain maximum - # compatibility), physical address line 20 is tied to low when the - # machine boots. Obviously this a bit of a drag for us, especially - # when trying to address memory above 1MB. This code undoes this. - + # For backwards compatibility with the earliest PCs, physical + # address line 20 is tied low, so that addresses higher than + # 1MB wrap around to zero by default. This code undoes this. seta20.1: inb $0x64,%al # Get status testb $0x2,%al # Busy? |