Intel processors run in 3 different modes: Real Mode Protected Mode Virtual Mode
Real mode is what the CPU boots into Protected Mode, processors ability to isolate programs in their own protected memory therefore those programs cannot know that other programs exist. The 386 can isolate programs in their own memory segment which ranges from one byte to 4Gb. With virtual memory support built in this
amount can be extended to 4TB (terabytes) Virtual Mode, enables the 386 etc. to create virtual processors (8086) complete with i/o trapping which can co-exist with protected mode programs