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1989-06-02
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DESQview 2.01 Technical Note:
Expanded Memory Specification Version 4.0
(EMS 4.0)
DESQview version 2.01 (or greater) supports the EMS 4.0 as well
as the EEMS and EMS 3.2 standards. Using a EMS 4.0 driver AND
a board designed to fully support the EMS 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 EMS 4.0 Hardware
The hardware features that identify whether an EMS board fully
supports the multi-tasking features of EMS 4.0 are:
1. ABILITY TO ADDRESS MORE THAN 64k OF CONTIGUOUS MEMORY AT
A TIME. EMS boards designed before EMS 4.0 utilize only
four adjoining 16K pages. A fully capable EMS 4.0
supporting board should be capable of supporting the
placement of EMS pages ANYWHERE within the first 1
Megabyte of address space (theoretically as many as 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 EMS 4.0 drivers
for their boards may soon be advertizing them as EMS 4.0 boards,
but that does not necessarily mean they are fully capable EMS 4.0
at the hardware level. If you are considering the purchase of a
EMS 4.0 board 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 EMS 4.0, so they should have tested it.
AST Research has announced that they will produce a EMS 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 EMS 4.0
driver for multi-tasking with existing AST hardware.
For readers of INFOWORLD, the December 12, 1988 issue has a very
good discussion of the hardware specifications of EMS 4.0 along
with a comparison of six boards (starting on page 54). We
recommend it to your attention.
* * * E N D O F F I L E * * *