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memspec.txt
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Title: Supported Memory Specifications
ID: Qualitas Technical Document 115
Product: 386MAX, BlueMAX
Date: 09/16/93
Supported Memory Specifications
-------------------------------
Qualitas MAX supports all of the leading PC memory specifications.
Among these standards are the EMS, XMS, VCPI, and DPMI specifications.
EMS Memory
----------
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
supersede 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 and 386MAX are registered trademarks, and BlueMAX and RAMexam
are trademarks of Qualitas, Inc. All other product names are
trademarks of their respective owners.
This technical note can be copied and distributed freely provided the
information is reproduced in its entirety and is not distributed for
profit.