Protected mode is not a destination. It is the moment a program realizes the walls were always optional.
Beyond the 640K barrier, beyond the Upper Memory Blocks and the High Memory Area and all the careful optimizations that squeeze life from a million bytes, there is more memory. Megabytes of it. The 80386 processor, with its 32-bit address bus, can see four gigabytes — a number so large that in 1991 it was not a quantity but a philosophical concept, like infinity but with a datasheet. The memory is there. It has always been there, sitting in the SIMM slots, electrically present, addressable in theory. But from inside the 640K, it might as well be another dimension. Real mode — the mode in which DOS operates, the mode in which the 8088’s 20-bit worldview is faithfully preserved even on processors that could do so much more — cannot see it. Real mode is a deliberate blindness, a backwards compatibility so thorough that a 33MHz 80486 pretends to be a 4.77MHz 8088 with the same conviction that a method actor brings to a role. The performance is flawless. The limitation is absolute. DOS ext...
From the lore of Conventional Memory.