DESQview

DESQview (DV) is a text mode multitasking operating environment developed by Quarterdeck Office Systems which enjoyed modest popularity in the late 1980s and early 1990s. Running on top of DOS, it allows users to run multiple programs concurrently in multiple windows. Quarterdeck's predecessor to DESQview was a task switching product called Desq (shipped late April or May 1984), which allows users to switch between running programs. Quarterdeck revamped its package, bringing multitasking in, and adding TopView compatibility. DESQview was released in July 1985, four months before Microsoft released the first version of Windows. It was widely thought to be the first program to bring multitasking and windowing capabilities to DOS; in fact, there was a predecessor, IBM TopView, which shipped March 1985,. Under DESQview, well-behaved DOS programs can be run concurrently in resizable, overlapping windows (something the first version of MS Windows cannot do). A simple hideable menu allows cutting and pasting between programs. DESQview provides support for simple editable macros as well. Quarterdeck also developed a set of optional utilities for DESQview, including a notepad and dialer. Later versions allow graphics mode programs to be loaded as well, but only run in full screen mode. 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. To make maximum use of extended memory on Intel 80386 processors, by transforming it into expanded memory and upper memory blocks (UMBs) accessible to DESQview and other real-mode programs, Quarterdeck developed a sophisticated memory manager.