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The Original Shareware 1.1
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The Original Shareware (WeMake CDs)(Volume 1.1)(CDs, Inc)(1993).iso
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LIM4-2.TEC
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1990-07-03
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ID:L4 Expanded memory with LIM 4.0 board
Why won't my LIM 4.0 board give me a Largest Available Expanded
Memory size greater than 0K?
---------------------------------------------------------------
The Largest Available Expanded Memory value indicates the largest
chunk of expanded memory that can be used to run a program in.
When this value is 0, no program can run in expanded memory;
multitasking can only occur in conventional memory.
Three things are necessary before any expanded memory board can
be used for multitasking with DESQview.
1) At least some memory below 640K must be able to take an
expanded memory map; it must have expanded memory management
hardware associated with it. For purchasers of expanded memory
boards for the PC, XT, and 286 AT, this means disabling
motherboard memory below 640K and filling out main memory with
the expanded memory board. The more memory disabled and
backfilled, the larger a chunk of expanded memory can be grabbed
at one time to run a program in.
2) The board must be capable of mapping pages of expanded memory
below 640K. If the board can't map pages of expanded memory
below 640K, there's no point in disabling main memory. If the
board can't map pages of expanded memory below, say, 256K,
there's no point in disabling main memory below 256K.
3) The driver that manages the expanded memory on the board must
be capable of mapping pages of expanded memory below 640K. Here
again, any limitation on the driver's power is a limitation on
the whole process.
If these three conditions are met, the Largest Available Expanded
Memory value will be equal to the amount of expanded memory that
has been mapped below 640K. For purchasers of expanded memory
boards, this means that the Largest Available Expanded Memory
value will be equal to the quantity of memory that has been
disabled on the motherboard and "backfilled" from the expanded
memory board.
(This exact equivalence is always the case for users with EGA and
VGA boards. Due to DESQview's ability to map additional memory
into available video areas above 640K, users of monochrome and
Hercules video cards may see a Largest Available figure that is
64K greater than the size of the backfill; CGA users may see a
figure 96K greater.)
The catch: properties #2 and #3 are OPTIONAL for boards that meet
the Lotus-Intel-Microsoft Expanded Memory Specification 4.0 (LIM
4.0). Let the buyer beware.
DESQview would also like expanded memory hardware and software to
permit the mapping of pages of expanded memory anywhere between
640K and 1024K. This property is very helpful in increasing the
size of Largest Available Conventional Memory in DESQview, and
the Largest Available Conventional Memory at the start of
DESQview is an upper limit on Largest Available Expanded Memory.
Again, this property is optional for boards that meet the LIM 4.0
specification.
It is worth repeating that, even with a Largest Available
Expanded Memory value of 0, you can still multitask as many
programs as will fit in conventional memory; and you can still
swap multiple programs in and out of expanded memory very
quickly. The one thing you cannot do with a Largest Available
Expanded Memory value of 0 is to multitask programs in expanded
memory. Programs that are swapped to expanded memory under these
circumstances are frozen until you swap them back into
conventional memory.