Developed by: Quarterdeck Office Systems
Launched: 1985

DESQview was a text-based multitasking operating environment developed by Quarterdeck Office Systems that enjoyed some popularity in the late 1980s and early 1990s, allowing users to run multiple programs simultaneously in multiple windows.

Originally, Quarterdeck developed a system that allowed the user to switch between tasks, called DESQ, which later led to the creation of DESQview.

DESQview was the first software to bring multitasking and window capabilities to DOS.
It allowed resizing and even overlaying windows (the first version of Windows, a few months later, was not able to overlay one window on top of another).
And through a menu, it was possible to copy and paste information between documents and programs.
It also allowed the use of simple macros.
All of this was achieved through a simple and easy-to-use user interface, but in text mode.

DESQview ran in real mode on a PC based on the Intel 8086 or Intel 80286. It made use of expanded memory.
However, its performance was most optimal on Intel 80386 machines, where it also ran in real mode instead of protected mode, which meant a program could crash the system.

To take full advantage of the extended memory on Intel 80386 processors, transforming it into expanded memory and upper memory blocks (UMBs) accessible to DESQview and other real-mode programs, Quarterdeck developed a sophisticated memory manager called QEMM (Quarterdeck Expanded Memory Manager). This was sold separately and proved more popular than DESQview itself.

Although DESQview was very robust and lightweight, Windows version 3.0 (which ran in graphical mode) eventually won out.