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Encyclopedia > EMM386

The name EMM386 was used for the expanded memory managers of both Microsoft's MS-DOS and Digital Research's DR-DOS, which created expanded memory using extended memory on Intel 80386 CPUs. Expanded Memory was a trick invented around 1984 that provided more memory to byte-hungry, business-oriented MS-DOS programs. ... Microsoft Corporation, (NASDAQ: MSFT, HKSE: 4338) is a multinational computer technology corporation with global annual revenue of US$44. ... Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ... Digital Research, Inc. ... This article is about the operating system. ... Extended memory refers to memory above the first megabyte of address space in an IBM PC with an 80286 or later processor. ... The Intel386[1] is a microprocessor which was used as the central processing unit (CPU) of many personal computers from 1986 until 2007. ...


The technique probably first appeared with the development of CEMM, included with Compaq DOS 3.31 in 1987. Microsoft's version first appeared, built-in, with Windows/386 2.1 in 1988 and as standalone EMM386.SYS with MS-DOS 4.01 in 1989; the more flexible EMM386.EXE version appeared in MS-DOS 5.0 in 1991. CEMM, for Compaq Expanded Memory Manager was probably the first so-called PC memory manager for Intel 80386 CPUs, able to transform extended memory into EMS expanded memory by using the virtual memory features and the virtual 8086 mode of the CPU. It was present in Compaq DOS 3. ... Windows 2. ... Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ...


Just as the other expanded memory managers, EMM386 uses the processor's virtual 8086 mode. It temporarily shuts down during a Windows session in 386 Enhanced mode, with Windows' protected mode kernel taking over its role. In the 80386 and later, Virtual 8086 mode, also called virtual real mode (or VM86), allows the execution of real mode applications that violate the rules under the control of a protected mode operating system. ... Protected mode is an operational mode of x86-compatible CPUs of the 80286 series or later. ...


EMM386.EXE can map memory into unused blocks in the Upper Memory Area, allowing device drivers and TSRs to be "loaded high", preserving precious Conventional memory. (For details, see Upper Memory Area.) The Upper Memory Area (UMA) is a feature of the design of IBM PC-compatible x86 computers. ... Terminate and Stay Resident (TSR) is a system call in DOS operating systems that returned control to the system as if the program had quit, but kept the program in memory. ... Conventional memory is the first 640 kibibytes of an IBM PCs memory. ... The Upper Memory Area (UMA) is a feature of the design of IBM PC-compatible x86 computers. ...


See also


  Results from FactBites:
 
EMM386 - Wikipedia, the free encyclopedia (156 words)
The name EMM386 was used for the expanded memory managers of both Microsoft's MS-DOS and Digital Research's DR-DOS, which created expanded memory using extended memory on Intel 80386 CPUs.
It also had other functions related to Windows, notably managing the virtualization of DOS windows and acting as the actual protected mode Windows kernel.
EMM386 could map memory into unused blocks in the Upper Memory Area, allowing device drivers and TSRs to be "loaded high", preserving precious Conventional memory.
Vernon Frazee: MS-DOS v6.22 Help: EMM386.EXE (1849 words)
EMM386 reserves this amount of extended memory for use as EMS/VCPI memory when EMM386 is loaded by the DEVICE=EMM386.EXE command in your CONFIG.SYS file.
When it is loaded, EMM386 reserves the amount of memory specified by the MIN switch for use as EMS/VCPI memory (the default value is 256K).
EMM386 may be able to convert additional amounts of XMS memory to EMS/VCPI memory, up to the amount specified by the MEMORY parameter.
  More results at FactBites »

 
 

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