Editing Real mode (section)

==History==
The 80286 architecture introduced [[protected mode]], allowing for (among other things) hardware-level memory protection. Using these new features, however, required a new [[operating system]] that was specifically designed for protected mode. Since a primary [[design specification]] of x86 microprocessors is that they are fully backward compatible with software written for all x86 chips before them, the 286 chip was made to start in 'real mode' – that is, in a mode which turned off the new memory protection features, so that it could run [[operating system]]s written for the [[Intel 8086|8086]] and the [[Intel 8088|8088]]. As of 2018, current x86 CPUs (including [[x86-64]] CPUs) are able to boot real mode operating systems and can run software written for almost any previous x86 chip without emulation or virtualization. In 2023 Intel proposed to drop real mode from future CPUs in the [[X86-64#X86S|X86S]] specification.

The PC [[BIOS]] which IBM introduced operates in real mode, as do the [[DOS]] operating systems ([[MS-DOS]], [[DR-DOS]], etc.).  Early versions of [[Microsoft Windows]] ran in real mode.  [[Windows/386]] made it possible to make some use of protected mode, and this was more fully realized in [[Windows 3.0]], which could run in either real mode or make use of protected mode in the manner of Windows/386. Windows 3.0 actually had several modes: "real mode", "standard mode" and "386-enhanced mode"; the latter required some of the virtualization features of the 80386 processor, and thus would not run on an 80286. Windows 3.1 removed support for real mode, and it was the first mainstream operating environment which required at least an 80286 processor. None of these versions could be considered a modern x86 operating system, since they switched to protected mode only for certain functions. [[Unix]], [[Linux]], [[OS/2]], [[Windows NT]] are considered modern OS's as they switch the CPU into protected mode at startup, never return to real mode and provide all of the benefits of protected mode all of the time. 64-bit operating systems use real mode only at startup stage, and the OS kernel will switch the CPU into [[long mode]].<ref>{{Cite web|title=Booting · Linux Inside|url=https://0xax.gitbooks.io/linux-insides/content/Booting/|access-date=2020-11-10|website=0xax.gitbooks.io}}</ref> Notably, the protected mode of the 80286 is considerably more primitive than the improved protected mode introduced with the 80386; the latter is sometimes called 386 protected mode, and is the mode modern 32-bit x86 operating systems run in.{{fact|date=May 2022}}