DESQview is not a GUI (Graphical User Interface) operating system. Rather, it is a non-graphical, windowed shell that runs in real mode on top of DOS, although it can run on any Intel 8086- or Intel 80286-based PC. It can also use expanded memory add-ons to work around the 640 kB RAM limit of conventional memory on early PCs. DESQview really came into its own on Intel 80386 machines, which are better at utilizing memory above DOS's limit. However, in either case, it runs in real mode rather than protected mode, meaning that a misbehaving program can still crash the system.