Quarterdeck Expanded Memory Manager (QEMM)

Blog Post created by billfox on Jan 16, 2019

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Quarterdeck Expanded Memory Manager (QEMM) is a memory manager produced by Quarterdeck Office Systems in the late 1980s through late 1990s. It was the most popular third-party memory manager for the MS-DOS and other DOS operating systems.


Memory management[edit]

Main article: DOS memory management

DOS was originally designed for the Intel 8086/8088 processor and therefore could only directly access a maximum of 1 MB of RAM. Due to PC architecture only a maximum of 640 KB (known as conventional memory) is available as the upper 384 KB is reserved.


QEMM Configurations[edit]

QEMM provides up to 635K free conventional memory (RAM under 640K), far better than pure MS-DOS EMM386, FreeDOS JEMM386, UMBPCI and many other memory manager programs. QEMM maximum RAM is 635K free conventional memory with up to 256MB XMS/256MB EMS shared.

MS-DOS 6.22, Windows 3.11/WFW 3.11[edit]

QEMM provides the best benefits to MS-DOS 6.22 or older since DOS's. MS-DOS 6.22 provides 619K free conventional memory and up to 64MB XMS/32MB EMS shared RAM. Assuming unaltered MS-DOS 6.22, without 3rd party utilities, i.e. JEMM, UMBPCI, etc. QEMM increases the available free conventional RAM to 635K with shared 256MB XMS/256MB EMS.

While using Windows 3.11 or Windows For Workgroups 3.11, QEMM provides additional free conventional memory for DOS Prompt running under Windows. QEMM is well suited for Windows 3.x as has supported for it since QEMM v5.x as early as 1990. As a result, QEMM 8.03 or QEMM 97 integrate very well with Windows 3.11/WFW 3.11.


Version history[edit]

Originally, the product was called QEMM-386 (require an intel 80386), and was released with a complementary product called QRAM (for use on intel 80286 and 8088). The 386 suffix was dropped starting with QEMM version 7.0 in 1993, when Intel released the Intel Pentium on 3/22/1993. The final release was re-branded as QEMM 97 to follow Microsoft's new branding trend of using year released instead of version numbers, specifically, Windows 95 and Windows 95 OSR2.


QEMM-386 v4.2 (1988-11-22)[edit]

  • Added support for intel 80486, DOS 4.01 and Windows 3.0.
  • Maximum RAM is 16MB XMS/16MB EMS.
  • LOADHI.SYS now loads 2 device drivers at a time.
  • New QEMM parameters include COMPAQ386S (C386S).
  • QEMM-386 v5.11 (1990-08)[edit]
  • QEMM supports moving and reallocating extended memory block, Virtual DMA Services (VDS) specification.
  • QEMM supports systems with large memory cache.


qemm loadhi.sys



QEMM - Wikipedia 

DOS - Wikipedia