

              NOVELL TECHNICAL INFORMATION DOCUMENT

TITLE:              EXPLAINING EXTENDED, EXTENDED VIA XMS & EXPAN
DOCUMENT ID:        TID800058
DOCUMENT REVISION:  A
DATE:               18AUG94
ALERT STATUS:       Yellow
README FOR:         NA

NOVELL PRODUCT and VERSION:
DR DOS 6.0

ABSTRACT:
This document gives a brief explaination of Extended Memory, Extended
via XMS Memory, and Expanded Memory as seen on a MEM display.

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VERIFY THIS INFORMATION.  HOWEVER, THE INFORMATION PROVIDED IN THIS
DOCUMENT IS FOR YOUR INFORMATION ONLY.  NOVELL MAKES NO EXPLICIT OR
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SYMPTOM:

When using the EMM386.SYS device driver, you may notice that the MEM
command can display a memory report that seems to show more memory
available than exists on your computer. For example, consider the
following EMM386.SYS device driver line on a computer with 3,072 KB
of Extended memory:

     DEVICE=C:\DRDOS\EMM386.SYS /F=AUTO /K=AUTO /B=FFFF /R=AUTO

This line has the effect of converting all Extended memory into
Extended via XMS and EMS (Expanded) memory. The resulting MEM report
might show that the computer has 3,072 KB of Extended memory and
3,072 KB of EMS memory under the TOTAL column, with 2,864 KB of
Extended via XMS memory and 2,864 KB of EMS memory under the
AVAILABLE column as shown below.


         - MEMORY TYPE ------- TOTAL ---------- AVAILABLE ---
        |                  |                |                |
        | Conventional     |    (    60K )  |    (   626K )  |
        | Upper            |    (    96K )  |    (    79K )  |
        | High             |    (    64K )  |    (    18K )  |
        | Extended         |    ( 3,072K )  |    (     0K )  |
        | Extended via XMS |        N/A     |    ( 2,864K )  |
        | EMS              |    ( 3,072K )  |    ( 2,864K )  |
         ----------------------------------------------------

SOLUTION:

To understand this, it might be helpful to view the total Extended
memory available on a computer as comprising a dynamic pool of
memory. This memory can be viewed as dynamic because it is available
to be accessed either as Extended via XMS memory or as EMS (Expanded)
memory depending on the /K setting on the EMM386.SYS device driver. 

In the case shown above, /K=AUTO tells EMM386.SYS to allow ALL of the
Extended memory pool to be accessed as Extended via XMS memory and
EMS memory in equal portions. The MEM command therefore shows both


amounts of memory as being available because there may be a need to
use a portion or all of the memory pool as either Extended via XMS
memory or EMS memory. The /K switch can be used to put a limit on the
amount of EMS memory to be created from the total memory pool. The
following EMM386.SYS device driver line on the same computer with
3,072 KB of Extended memory will limit the amount of EMS memory to be
created from the total memory pool by setting the /K option to
/K=1024:

     DEVICE=C:\DRDOS\EMM386.SYS /F=AUTO /K=1024 /B=FFFF /R=AUTO

This line will still cause EMM386.SYS to convert all of the memory
pool into Extended via XMS, but it will limit the amount of EMS to
1,024 KB. The resulting MEM report might show that the computer has
3,072 KB of Extended memory and 1,024 KB of EMS memory under the
TOTAL column, with 2,864 KB of Extended via XMS memory still
available but only 896 KB of EMS memory under the AVAILABLE column as
shown below.


         - MEMORY TYPE ------- TOTAL ---------- AVAILABLE ---
        |                  |                |                |
        | Conventional     |    (   640K )  |    (   626K )  |
        | Upper            |    (    96K )  |    (    79K )  |
        | High             |    (    64K )  |    (    17K )  |
        | Extended         |    ( 3,072K )  |    (     0K )  |
        | Extended via XMS |        N/A     |    ( 2,864K )  |
        | EMS              |    ( 1,024K )  |    (   896K )  |
         ----------------------------------------------------

Notice in both of the above examples, that there is a difference
between the TOTAL of Extended memory and the AVAILABLE bytes of
Extended via XMS memory and a similar difference between the TOTAL of
EMS memory and the AVAILABLE bytes of EMS memory. This is due to the
amount of overhead memory used by the EMM386.SYS software to convert
the memory pool into both types of available memory.

XMS memory is Extended memory created by memory management software
which conforms to the XMS specification developed by Lotus, Intel,
and Microsoft (LIM). The DR DOS memory management software device
driver (EMM386.SYS) fully supports this specification and, as a
result, initially converts ALL of the computer's available Extended
memory into XMS Extended memory. This is the reason that there is no
Extended memory listed in the AVAILABLE column of the DR DOS MEM
report.  It has all been converted to XMS memory by the EMM386.SYS
device driver. This is also the reason why Extended via XMS lists as
N/A under the TOTAL column; XMS memory is created by a software
device driver and is not present at boot time.

EMS memory is listed with a specific value under the TOTAL column by
the MEM report unlike the Extended via XMS listing. EMS memory can be
created by a software device driver (like EMM386.SYS alone) or can be
created by EMS (LIM 4.0) hardware memory boards and their
accompanying device driver. This specific value is intended to
reflect the EMS memory created by the /K option on the EMM386.SYS
device driver line.   This value could also be created by certain
hardware platforms, typically non- 386/386sx/486 platforms, which
actually contain EMS (LIM 4.0) hardware.

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