DOCUMENT:Q71865 26-NOV-1999 [msdos] TITLE :Requirements for UMB Support in MS-DOS 5.0 PRODUCT :Microsoft Disk Operating System PROD/VER:MS-DOS:5.0 OPER/SYS: KEYWORDS:msdos ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft MS-DOS operating system version 5.0 ------------------------------------------------------------------------------- SUMMARY ======= MS-DOS version 5.0 provides systems the ability to free up conventional memory by running device drivers and other memory resident programs in the upper memory blocks (UMBs) located in the upper memory area (UMA). The UMA is address space located between 640K and 1024K that normally contains the system ROM BIOS and the video, network, and other hardware adapters. To access MS-DOS 5.0's ability to support UMBs, Microsoft recommends the following system conditions be met: - A 80386 or 80486 microprocessor - 350K of XMS memory - The following CONFIG.SYS statements: device=himem.sys dos=umb or dos=high,umb device=emm386.exe noems or device=emm386.exe ram Any DEVICEHIGH statements in the CONFIG.SYS file must follow the two device statements previously mentioned. MORE INFORMATION ================ 80386 or 80486 Microprocessor ----------------------------- The 80386 and 80486 are the first processors that have paging hardware capability. EMM386.EXE uses this capability to map device drivers or programs into the UMA where these programs run in real-mode addresses that are below the 1024K line. Therefore, EMM386.EXE can currently work only with these microprocessors. For any earlier processor, a different upper memory manager is necessary for access to that area. 350K of XMS Memory ------------------ XMS is the Lotus/Intel/Microsoft/AST eXtended Memory Specification, which is a standard way for programs to use extended memory. 350K is the recommended amount of XMS memory necessary to use all of the UMA for UMBs. However, it is possible to have a smaller amount of XMS memory for UMB support. Most often, 350K of UMBs will never be available due to the system ROM BIOS and other hardware adapters that may be present in the UMA. CONFIG.SYS Statements --------------------- The following MS-DOS 5.0 statements are needed for UMB support: - The DEVICE=HIMEM.SYS statement loads the extended memory manager driver that provides access to extended memory. - DOS=UMB provides MS-DOS the link to the UMA providing UMB support. - The EMM386.EXE statement needs one of the following switches to manage the UMA: noems (Does not provide expanded memory support) ram (Provides both upper memory and expanded memory support) Examples: device=c:\dos\emm386.exe noems device=c:\dos\emm386.exe ram More information on this topic can be found in the version 5.0 "Microsoft MS-DOS User's Guide and Reference," pages 313-330. Additional query words: 5.00 noupd ====================================================================== Keywords : msdos Technology : kbMSDOSSearch kbMSDOS500 Version : MS-DOS:5.0 ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 1999.