Last modified: Thu Jun 25 10:25:40 UTC+0200 2026 © A. Tarpai

Protected Mode

The 286 introduced the Protected mode extension in 1982.

Intel Protected Mode is a big all-in-one package: new hardware model, new registers, instructions, structures in memory and complex CPU operation mechanisms.

Protected Mode is essentially unchanged since the 286 – so it's interesting to look at. At the same time, how the 32-bit 386 implemented and extended on top of this 16-bit p-mode. The aim is how the cpu works and not some complete p-mode OS writing.

Protected Mode mode is either on- or off by setting one new CPU control bit, the PE-bit:

• It alters CPU operation and turns on Protected Mode mechanisms.
• The hardware model remains fixed and made so that it can be used for 8086 emulation (RM) and 286 p-mode emulation (running 16-bit p-mode code, 386+).