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. --------------------------------------------------------------------- DISCLAIMER: THE ORIGIN OF THIS INFORMATION MAY BE INTERNAL OR EXTERNAL TO NOVELL. NOVELL MAKES EVERY EFFORT WITHIN ITS MEANS TO VERIFY THIS INFORMATION. HOWEVER, THE INFORMATION PROVIDED IN THIS DOCUMENT IS FOR YOUR INFORMATION ONLY. NOVELL MAKES NO EXPLICIT OR IMPLIED CLAIMS TO THE VALIDITY OF THIS INFORMATION. --------------------------------------------------------------------- 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. --------------------------------------------------------------------- Any trademarks referenced in this document are the property of their respective owners. Consult your product manuals for complete trademark information. ---------------------------------------------------------------------