About comment in setup.s

[ZebinRenTmp]

in setup.s line 183
enable the A20 line will allow referencing to memory above 1MB, not 64KB

[yhshu]

If there's not segmentation mechanism, the memory range is 64K without A20 line; if you use the segmentation mechanism, the memory range is 1M without A20 line.
I believe you're reading one of the tags instead of the master, maybe you should tell us the tag.