QEMM
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QEMM, the Quarterdeck Expanded Memory Manager by Quarterdeck, was a popular memory manager for the DOS operating system. QEMM provides access to the Upper Memory Blocks (UMBs), Expanded Memory Specification (EMS) memory and Extended Memory Specification (XMS) memory. Many DOS programs required a high amount of conventional memory, and QEMM helped to increase the amount of free conventional memory by loading programs to the UMBs. Many programs, such as Lotus 1-2-3, early version of Microsoft Windows, and many games, also used the EMS and XMS memory.
Originally, it was called QEMM-386, and had a complementary product called QRAM that worked in a similar manner on 286's that had some specific Chips and Technologies chipsets. The 386 was dropped when the Intel Pentium was released. QEMM-386 and DESQview could cooperate and when shipped as a bundle were called DESQview 386.
The principal competitors of QEMM were BlueMax/386Max, and HeadRoom/NetRoom.
Compaq DOS 3.31, released in 1987 or 1988, was the first DOS operating system to bundle technology similar to QEMM-386 with the OS itself, incorporating a 386-mode EMS manager called CEMM. It is uncertain which software was released first, CEMM or QEMM.
Digital Research's DR-DOS 5.0 (1990) was the first non-vendor-specific DOS to offer this technology, incorporating a 386-mode XMS/EMS manager called EMM386. Microsoft released comparable but simpler memory managers of its own - HIMEM.SYS for XMS and EMM386.EXE for EMS with Windows 3.0 in 1990 as well; they could be used outside of Windows sessions; earlier Windows/386 2.1 included a built-in EMM which offered EMS to DOS windows during Windows sessions only. HIMEM and EMM386 became part of MS-DOS with version 5.0 (1991). MS EMM386 required HIMEM to be loaded first, while DR's EMM386 fulfilled both rôles and did not need HIMEM, which was only needed on 286 machines.
Neither DR's nor MS's memory managers were as capable as QEMM - for example, both required Upper Memory Blocks to be manually discovered and included, whereas QEMM could do this quite satisfactorily on its own. QEMM also did not require to predefine how much memory should become EMS and how much should be XMS, therefore it was not necessary to juggle boot configurations. However, although QEMM still usually freed up more conventional memory than EMM386 did, the bundled system did a usable job and QEMM's market share began to slide.
While popular when DOS programs were the mainstream, QEMM eventually became irrelevant as Windows programs replaced DOS programs. The final version was QEMM 8, which was compatible with Windows 95 and later Windows 98, but by this point, DOS applications were largely obsolete and thus so was DOS memory optimisation.