ID:D4 DOS 4.0 and Expanded Memory Drivers
DESQview 2.+ Technical Note #143

We have tested all of our products under DOS 4.0 and above and 
have not found any problems, other than those mentioned below 
under the heading "Consumer Alert! - Using the '/X' parameter."

DOS's Expanded Memory Drivers

DOS 4.0 provides two files, XMAEM.SYS and XMA2EMS.SYS, that can be 
used to provide expanded memory on some systems.  
     
     XMAEM.SYS:  This driver is used to emulate an IBM XMA card 
     on 386 IBM machines.  XMA is an IBM hardware specification 
     which uses a bank-switching technique.  It should be noted 
     that on a hardware level, this technique is not EMS 3.2, EEMS 
     or EMS 4.0.  It is IBM's own method.  The IBM 3270 
     Workstation program uses XMA in its native mode, but any 
     program that uses LIM style memory requires an additional EMS 
     emulation driver on top of XMAEM.SYS systems or XMA boards.

     XMA2EMS.SYS:  This driver, when used with a 386 that has 
     XMAEM.SYS loaded or when used with an XMA board, emulates 
     EMS 4.0.  This driver seems to do a reasonably good job of 
     emulating the EMS 4.0 spec, but is of limited use to DESQview 
     users in that it cannot set EMS pages in the 0-640K area and 
     cannot be made to set pages into high (640K-1 meg) memory 
     addresses other than the EMS 64K page frame.  This driver 
     can be used for DESQview program swapping, but not to 
     support multitasking in expanded memory.


Consumer Alert! - Using the "/X" Parameter

DOS 4.0 defines EMS 4.0 pages 254 and 255 to be reserved for the 
use of the DOS 4.0 utilities BUFFERS, FASTOPEN and VDISK.  This 
function can be utilized by allocating specific physical 16K 
pages for P254 and P255 on the expanded memory driver line in 
CONFIG.SYS.  These three utilities can then access this memory by 
giving them a "/X" parameter.  

This represents an addition to the EMS 4.0 specification by IBM, 
an addition which is not supported by the specification as 
outlined by Lotus, Intel and Microsoft.  It is not supported by 
Quarterdeck's QEMM driver or any other EMS 4.0 driver other than 
IBM's.  Quarterdeck believes that users with IBM DOS 4.00 or 4.01 
or MS-DOS 4.00 should not use the "/X" switch to load any of the 
above-mentioned utilities, as other EMS 4.0 software will not be 
able to detect this special usage of EMS and may overwrite these 
pages.  Since the BUFFERS driver contains directory information, 
this could lead to the loss of information on your hard disk.

Under the appropriate circumstances, later versions of DOS 4 
can be safely permitted to use expanded memory for loading 
BUFFERS, FASTOPEN and VDISK.  If you are using our Manifest 
product, it can detect whether your system is currently configured 
to use "/X" safely or not.  To find out, boot up without using the 
"/X" parameter and then look at Manifest's "Hints."  If one of the 
hints is to load your BUFFERS with the "/X" parameter, then you 
may assume it is safe to use.  If you are unsure about whether 
your DOS can safely use the "/X," we strongly recommend you do not 
use the "/X" parameter for BUFFERS, FASTOPEN and VDISK at any 
time, whether using our products or not.

                        ****************

Comparison of XMAEM and XMA2EMS and DESQview's QEMM products:

Unless you don't have the QEMM products, there is no particular 
reason to use the IBM drivers.  

On a 386:  IBM's drivers (both of which must be used), take 19K 
of conventional memory overhead vs. 1.5K for QEMM.  They do not 
provide memory sorting, loading high of TSR's, or caching of ROMS; 
DESQview users will not get virtual screen support, and the memory 
mapped by the IBM drivers can only be used by DESQview for swap 
space, not for multitasking programs.  Even if you don't plan to 
run DESQview or load TSRs into high memory,  QEMM is probably a 
faster and more robust driver.

On expanded memory boards:  The IBM drivers cannot be used on 
these boards.  Only IBM XMA boards or 386 extended memory can 
support the drivers.  You will still need to run the expanded 
memory driver that came with the board.

On Model 50/60 with memory expansion:  If you are not running 
DESQview, the IBM drivers will probably work well for expanded 
memory programs such as Lotus 1-2-3, but do not provide the 
motherboard or 640K-1 meg mapping that is desirable for multi-
tasking programs and loading TSRs into high memory.

        Copyright (C) 1991 by Quarterdeck Office Systems
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