Another interesting usage of LOADALL, laid out in the book "The Design of OS/2", would have been to allow running former real-mode programs in 16-bit protected mode, as utilized by Digital Research's Concurrent DOS 286 since 1985, as well as FlexOS 286 and IBM 4680 OS since 1986. Marking all the descriptor caches in the GDT and LDTs "not present" would allow the operating system to trap segment-register reloads, as well as attempts at performing real-mode–specific "segment arithmetic" and emulate the desired behavior by updating the segment descriptors (LOADALL again). This "virtual 8086 mode" for the 80286 was, however, too slow to be practical. The idea had to be mostly discarded, furthermore, due to errata in some early Intel 80286 processors before the E-2 stepping. As a result, OS/2 1.x – and Windows in "standard" mode as well – had to run DOS programs in real mode. Nevertheless, the idea was not lost; it led Intel to introduce the virtual 8086 mode of the 80386, allowing the implementation of "DOS boxes" at last in a relatively efficient and documented way.