The 80286 introduced "Protected Mode" in 1982. It was not popular. The mode was difficult to use, lacked paging, and offered no way to return to real mode without a hardware reset. The 80386, arriving three years later, made protection usable -- adding paging, a flat 32-bit address space, per-page User/Supervisor control, and Virtual 8086 mode so that DOS programs could run inside a protected multitasking system. These features made possible Windows 3.0, OS/2, and early Linux.
self.seen_urls.add(url)
，这一点在同城约会中也有详细论述
A pod of dolphins circled the craft.
"People didn't always carry the donor card on them in their pockets and handbags and the nurses and doctors didn't have time to look through. So there was a problem," Cox said.