DESQview and QEMM
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. Owing to the foresight of its marketing manager, Quarterdeck marketed it as a separate product, QEMM-386 (Quarterdeck Expanded Memory Manager 386). It became more popular than DESQview itself, and sold steadily for many years, generating over US$150 million in sales from 1987 through 1994. After the release of the Intel Pentium processor, the 386 in QEMM was dropped. The combination package of DESQview and QEMM-386 was called DESQview 386.
With the introduction of the 80386, the memory management features were enhanced to allow the system to be shifted into protected mode but also allowing the addresses to be configured in a virtual 8086 mode so that the extended memory could be mapped into addressing frames and accessible to real-mode programs such as MS-DOS. This allowed a 386 to implement the LIM (Lotus, Intel, Microsoft) EMS (expanded memory specification). The memory manager was easily controlled by the user with DOS program QEMM.COM
DESQview was able to use QEMM's features far beyond just the LIM EMS API, mapping most of the "conventional" address space (below 640 KB) into multiple extended memory blocks such that each could execute transparently during its context. The main copy of DOS and any device and networking drivers had to be loaded before DESQview. The resulting space was the largest single program that could run, but DESQview under QEMM could run as many instances of those programs as the EMS would allow. So an 8 MB system could generally have a dozen full-sized MS-DOS programs running concurrently; a 16 MB system could run over twenty, and so on.
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