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MEMSPEC.TXT
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1992-08-27
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102 lines
Supported Memory Specifications
───────────────────────────────
386MAX and BlueMAX support all of the leading PC memory specifications.
Among these standards are the EMS, XMS, VCPI, and DPMI specifications.
EMS Memory
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The Expanded Memory Specification ( EMS ) was developed by Lotus
Development Corporation, Intel Corporation, and Microsoft Corporation. The
EMS specification outlines a means by which resources above the 1MB
boundary can be accessed by programs which are EMS aware. Expanded memory
is provided by a software driven EMS manager which controls the EMS
resources. While systems with 80386 or later microprocessors can directly
emulate EMS with only a software driver, earlier architectures require
hardware support in the form of a LIM EMS card.
EMS memory above the 1MB boundary is configured in 16 KB units called
pages. The memory cannot be accessed directly since the scope of DOS is
limited to the first megabyte. Instead the pages are obtained by virtually
remapping them through a 64 KB 'window' in memory known as the page frame.
To obtain a copy of the EMS specification, write to:
Intel CO3-07
5200 NE Elam Young Parkway
Hillsboro, OR 97124
XMS Memory
──────────
The eXtended Memory Specification ( XMS ) allows for the orderly allocation
of extended memory resources. The specification outlines three different
regions of memory known as Upper Memory Blocks ( UMBs ), Extended Memory
Blocks ( EMBs ), and the High Memory Area ( HMA ).
The UMBs consist of the unused area between the system hardware found in
the region between physical addresses 640 KB and 1 MB. This area is also
used by memory managers and is commonly referred to as high DOS. By using
functions detailed in the XMS specification, many resident programs can
load resources into UMBs automatically. This reduces the overhead found in
the first 640 KB.
The HMA is the 64KB area starting at 1024KB and can be used by only one
program at a time. It is commonly used by system software such as DOS 5.0
(as well as DR DOS 5.0 and later) to load the bulk of the DOS kernel out
of the first 640 KB. The EMBs simply consist of extended memory above 1088
KB (1MB + 64KB).
To obtain a copy of the XMS specification, write to:
Microsoft Corporation
16011 NE 36th Way
P.O. Box 97017
Redmond, WA 98073
VCPI
────
The Virtual Control Program Interface ( VCPI ) memory specification
outlines a client-host relationship which allows more than one protected
mode program to execute at the same time. Since the VCPI interface is an
extension of the EMS specification, the VCPI server allocates EMS rather
than extended memory. The specification was originally developed by Phar
Lap Software, Inc. and Quarterdeck Office Systems.
DPMI
────
The DOS Protected Mode Interface ( DPMI ) is a relatively new memory
specification. The interface allows more than one protected mode
application to execute at a time much like VCPI, but the DPMI server
retains more control than a VCPI server in order to better ensure the
integrity of the system. Protected mode applications also tend to be
easier to develop under DPMI. For these reasons, DPMI will likely
supercede VCPI in the future.
To obtain a copy of the DPMI specification, write to:
Intel Literature JP26
3065 Bowers Avenue
P.O. Box 58065
Santa Clara, CA 95051
----------
Qualitas, Inc. Main : (301) 907-6700
7101 Wisconsin Avenue Sales : (800) 733-1377
Suite 1386 FAX : (301) 907-0905
Bethesda, MD 20814-4805 BBS : (301) 907-8030
CompuServe : 73377,3307
MCI : 336-2907
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386MAX, BlueMAX, and MOVE'EM are trademarks of Qualitas, Inc.
All company names and products are trademarks or registered trademarks
of their respective companies.