The trick you describe was being used by Silicon Valley Computer ADP50L IDE controller from early nineties (1991). Memory mapped I/O instead of traditional x86

The trick you describe was being used by Silicon Valley Computer ADP50L IDE controller from early nineties (1991). Memory mapped I/O instead of traditional x86 port access lets you skip doing manual loop for 'rep movsb', result can be 50% speed bump https://forum.vcfed.org/index.php?threads/performance-of-lo-tech-isa-compactflash-adapter.54821/ https://forum.vcfed.org/index.php?threads/performance-of-lo-... Port IO Read Speed : 219.39 KB/s MMIO Read Speed : 310.77 KB/s Some variants of XTIDE hardware also implement this, as does the free bios.