Page "OS/2" Paragraph 22

Because of the limitations of the Intel 80286 processor, OS / 2 1. x could run only one DOS program at a time, and did this in a way that allowed the DOS program to have total control over the computer.

A problem in DOS mode could crash the entire computer.

In contrast, OS / 2 2. 0 could benefit from the virtual 8086 mode of the Intel 80386 processor in order to create a much safer virtual machine in which to run DOS programs.

This included an extensive set of configuration options to optimize the performance and capabilities given to each DOS program.

Any real mode operating system ( such as Xenix ) could also be made to run using OS / 2's virtual machine capabilities, subject to certain direct hardware access limitations.