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Encyclopedia > CEMM

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. Compaq Computer Corporation was founded in February 1982 by Rod Canion, Jim Harris and Bill Murto, three senior managers from semiconductor manufacturer Texas Instruments. ... A memory manager is a part of a computer program which accepts requests from the program to allocate and deallocate chunks of memory. ... An Intel 80386 Microprocessor The Intel 80386 is a microprocessor which was used as the central processing unit (CPU) of many personal computers from 1986 until 1994 and later. ... Extended memory refers to memory above the first megabyte of address space in an IBM PC with an 80286 or later processor. ... Expanded Memory is memory used through EMS. In systems based on Intel 80386 or later processors expanded memory is part of the extended memory that is mapped into the expanded memory page frame by the processor. ... Virtual memory is a computer design feature that permits software to use more main memory (the memory which the CPU can read and write to directly) than the computer actually physically possesses. ... In the x86 CPU architecture Virtual 8086 mode, also called virtual-real mode, allows the emulation of real mode in protected mode. ...


It was present in Compaq DOS 3.31, in 1988 or before. 1988 is a leap year starting on a Friday of the Gregorian calendar. ...


Together with IBM, Compaq was the first vendor to propose computers based on the 386 CPU and it was natural for them to develop solutions leveraging the specific features of their new hardware and in this case allowing existing EMS-compatible DOS programs to access all the memory. International Business Machines Corporation (IBM, or colloquially, Big Blue) (NYSE: IBM) (incorporated June 15, 1911, in operation since 1888) is headquartered in Armonk, New York, USA. The company manufactures and sells computer hardware, software, and services. ...


Alas, interesting features often come with less interesting drawbacks. Although CEMM was called an "expanded memory manager", it was really a tiny, protected mode, single tasking operating system kernel, also called a virtual machine monitor. It had to catch all the interrupts and all the exceptions, and to reflect them to the virtual machine where DOS ran. This slowed the machine down a little, increased the latency of interrupts and changed the behavior of DOS programs trying to execute invalid machine instructions. In general terms, a virtual machine in computer science is software that creates an environment between the computer platform and the end user in which the end user can operate software. ...


Because CEMM put the CPU into protected mode, other programs (DOS extenders) could not do this anymore by themselves. A special API, the VCPI, had to be developed to allow running DOS extender programs. The first CEMM compatible with VCPI was 4.0, provided with Compaq DOS 4.01. DOS extender is a rather curious name invented in the 1980s for programs started from MS-DOS, but which actually need to run in protected mode. ... DPMI is the method which Microsoft prescribes for a DOS program to run in protected mode and to access extended memory under a multitasking operating system like Microsoft Windows. ...


Compaq has a 1987 patent on the technology, and they were probably the creators and the first company to use it. However, over time, QEMM and 386/MAX became the standard packages. Windows/386 2.1 and later releases contained a built-in expanded memory manager (EMM386) available during Windows sessions and otherwise used for running multiple DOS virtual machines. DR-DOS 5.0 (in 1990) and MS-DOS 5.0 (in 1991) officialized the technology outside of the Windows context. QEMM, the Quarterdeck Expanded Memory Manager by Quarterdeck, was a popular memory manager for the DOS operating system. ... Microsoft Windows 2. ... DR-DOS is an MS_DOS_compatible operating system for IBM PC_compatible personal computers, originally developed by Gary Kildalls Digital Research and derived from CP/M_86. ... 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. ...


External link

  • U.S. Patent 4,926,322 (http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=4,926,322.WKU.&OS=PN/4,926,322&RS=PN/4,926,322) - Software emulation of bank-switched memory using a virtual DOS monitor and paged memory management

  Results from FactBites:
 
CEMM - Wikipedia, the free encyclopedia (348 words)
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.
Although CEMM was called an "expanded memory manager", it was really a tiny, protected mode, single tasking operating system kernel, also called a virtual machine monitor.
The first CEMM compatible with VCPI was 4.0, provided with Compaq DOS 4.01.
BioMed Central | Full text | Chemically defined medium and Caenorhabditis elegans (3030 words)
Animals grown on 1.7% agar CeMM plates, reached a length of 1 mm in times not significantly different from those in liquid CeMM (Table 2), implying growth rate differences are the effect of CeMM composition but not the physical state.
CeMM composition changes as the result of animal growth in the medium and growth rates are consequently altered as the medium changes.
Mixed stage animals grown in liquid CeMM can be directly mixed 1:1 with freezing medium [4,7] and slowly frozen to -80°C. Compared to typical starved L1 freezes prepared from NGM grown animals, larger numbers of animals are viable after three years.
  More results at FactBites »

 
 

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