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LIM4.TEC
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1990-07-05
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DESQview 2.01 Technical Note:
Lotus/Intel/Microsoft Expanded Memory
Specification 4.0 (LIM 4.0)
DESQview version 2.01 (or greater) supports the LIM 4.0 as well
as the EEMS and LIM 3.2 standards. Using a LIM 4.0 driver AND
a board designed to fully support the LIM 4.0 specification,
DESQview can support multi-tasking beyond the 640K barrier in a
manner that previously could only be achieved with an Enhanced
expanded memory card (EEMS).
While the EMS 4.0 specification supports multitasking in expanded
memory, boards designed for the EMS 3.2 spec cannot support this
feature, even with an EMS 4.0 driver.
I quote PC Week Magazine (Nov. 3, 87):
"Currently, none of Intel Corp.'s AboveBoard EMS products,
for instance, support multitasking, since all were designed
for their own EMS 3.2.
'We're offering a 4.0 driver with our boards, but you still
won't be able to get multitasking performance.' conceded
Rich Bader, general manager of Intel's PC products division.
'However,'he noted,'the only thing not privided is concurrency.
In all other areas, our boards support all the new features of
EMS 4.0.'."
DESQview continues to support the swapping of programs to EMS 3.2
hardware with an EMS 4.0 driver and will support multitasking on
EMS 4.0 specific hardware with the EMS 4.0 driver.
Identifying LIM 4.0 Hardware
The hardware features that identify whether an EMS board fully
supports the multi-tasking features of LIM 4.0 are:
1. ABILITY TO ADDRESS MORE THAN 64k OF CONTIGUOUS MEMORY AT
A TIME. EMS boards designed before LIM 4.0 utilize only
four adjoining 16K pages. A true LIM 4.0 supporting
board should be able to concurrently map AT LEAST 64 16K
pages.
2. ABILITY TO MAP THIS MEMORY BELOW THE 640K BARRIER. As
with an EEMS board, it is necessary to have memory from
an EMS 4.0 board backfill motherboard memory in order to
obtain EMS 4.0 partitions in expanded memory that will
be of sufficient size to run most large programs. The
section of the board that backfills lower memory, plus
any remaining space above 640K to the base address of
the video card determines the size of this contiguous
paging area.
It is quite possible that companies that develop LIM 4.0 drivers for
their boards may soon be advertizing them as LIM 4.0 boards, but that
does not make them so. If you are considering the purchase of a LIM
4.0 and would like it to run properly with DESQview, you should call
the manufacturer to confirm that the HARDWARE supports these features -
AND ask if they have tested with DESQview. DESQview is one of the
first and best known programs to specifically support LIM 4.0, so they
should have tested it.
AST Research has announced that they will produce a LIM 4.0 driver
that will be fully functional with their EEMS boards. DESQview is
expected to utilize either the older EEMS driver or the newer LIM 4.0
driver for multi-tasking with existing AST hardware.
As of 1/1/88, the only boards that have been announced that fully
support LIM 4.0 are for the IBM PS/2 series, but we would expect
fully functional LIM 4.0 boards to become available for PC,XT and
AT computers during the first half of 1988.
* * * E N D O F F I L E * * *