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AXCEL216's MAX Speeed MS-DOS MEMORY TYPES, ARCHITECTURE, REGIONS + MAPPING NOTES: * For memory management guide + optimization tips *READ* MEMORY.TXT (included). * For DOS + Windows extended + expanded memory managers technical details see EMM386.TXT (included). * For abbreviations + terms explanations see GLOSSARY.TXT (included). * For Microsoft EMM386.EXE + HIMEM.SYS undocumented parameters see related topics in SECRETS.TXT (included). Memory mapping resources on the Internet: - PC Guide - Logical Memory Layout: http://www.pcguide.com/ref/ram/logic.htm - Microsoft XMS 3.0 Specification [XMS30.TXT, 163 KB, free]: ftp://ftp.microsoft.com/softlib/mslfiles/XMS.EXE - PC Memory Tutorial: http://cma.zdnet.com/book/upgraderepair/ch07/ch07.htm REGIONS.TXT Contents: I. MS-DOS MEMORY TYPES + ARCHITECTURE: 1. Conventional Memory [below the 1st MegaByte] 2. Extended and Expanded Memory: [above the 1st MegaByte] A. Extended Memory ["longer"] B. Expanded Memory ["fatter"] II. MS-DOS UPPER MEMORY REGIONS + MAPPING III. MY ADDENDUM ON UPPER MEMORY REGIONS MANAGEMENT ______________________________________________________________________________ I. MS-DOS MEMORY TYPES + ARCHITECTURE I compiled this topic based mostly on Raymond Dunn's public domain USENET article [EXT-RAM.TXT, 5 KB]: http://www.simtel.net/pub/simtelnet/msdos/info/ext_ram.zip and included current PC memory specifications and technology updates. My most sincere *THANKS* go to Raymond for his valuable contribution to these files! 1. Conventional Memory [below the 1st MegaByte] Memory is measured in Bytes. Each Byte contains 8 bits. The bit (binary digit) is the basic unit of (digital) information, and can be either 0 or 1. Computer data (i.e. memory or disk capacity) is measured using the hexadecimal system (base of 16). Multiples for Byte: - 1 KiloByte = 1,024 Bytes. - 1 MegaByte = 1,024 KB = 1,048,576 B. - 1 GigaByte = 1,024 MB = 1,048,576 KB = 1,073,741,824 B. - 1 TeraByte = 1,024 GB = 1,048,576 MB = 1,073,741,824 KB = etc... Memory addresses and ranges use the hexadecimal (hex) notation: numbers 0 to 9 and letters A to F, allowing 16 possible values for each hex digit. MS-DOS (MicroSoft Disk Operating System) was designed around the original 8088 Intel CPU which was [and still is :(] able to address only up to 1 MegaByte (MB) of memory (RAM), called "Conventional memory", and located between 0K and 1M [1 MB = 64 pages]. This space is divided into two major blocks: - 0K - 640K [640 KB = 40 pages] = "Low (DOS) RAM", used by software: MS-DOS core/system, I/O, programs, drivers, TSRs etc. - 640K - 1M [384 KB = 24 pages] = "High RAM", used by hardware: ROM, BIOS, Video, HDC etc. Conventional memory can be divided into 64 pages of 16K each, refered to as page 0, page 1, page 2, and so on, or by their hexadecimal segment addresses: page 0 at segment 0, page 1 at segment 0400, page 2 at segment 0800 etc. Examples of page numbers with corresponding segment and linear addresses: Page Segment Address Linear Address ---------------------------------------------- 0 0000 0K 1 0400 16K 2 0800 32K 4 1000 64K 8 2000 128K 12 3000 196K 40 A000 640K 63 FC00 1008K 1st MegaByte memory map [0000 - FFFF = 1M] usage on a typical X86 PC: Address Range Used by Size ---------------------------------------------- 0000 - 0FFF Low DOS RAM 640 KB A000 - AFFF VGA graphics 64 KB B000 - B7FF Monochrome video 32 KB B800 - BFFF VGA text 32 KB C000 - C7FF Video and HDC ROM 32 KB C800 - CFFF Available to DOS 32 KB D000 - DFFF EMS page frame 64 KB E000 - EFFF Available to DOS 64 KB F000 - FFFF BIOS and FDC ROM 64 KB To see a graphical map of all modules/programs/drivers using the memory below the 1st MegaByte, their sizes, the free memory status with specific hex address locations and the available memory blocks, run: MSD and press M. To see a detailed list of all modules/drivers using the memory below the 1st MegaByte, their sizes and the free memory status with specific hex address locations, run: MEM /A /D /P To see a classified list of all programs/drivers using the memory below the 1st MegaByte, their sizes, the free memory summary and the available memory blocks, run: MEM /A /C /P These commands can be executed either from the native/real MS-DOS mode or in a DOS box/session within MS Windows GUI. The undocumented "MEM /A" command line parameter is explained in "MEM.EXE HIDDEN PARAMETERS" in SECRETS.TXT (included). For more details take a look at: * These MSD (MicroSoft Diagnostics utility) reports in: - MSD95.TXT (part of W95-11D.ZIP) = Win9x/DOS7 users. - MSD62.TXT (part of W31-11D.ZIP) = Win31/DOS6 users. * These "MEM /A /C /P" stats in: - DOS95MEM.TXT and WIN95MEM.TXT (both part of W95-11D.ZIP) = Win9x/DOS7 users. - MEM62.TXT and MEM31.TXT (both part of W31-11D.ZIP) = Win31/DOS6 users. To comply with the "industry standard" IBM PC/AT architecture, this memory is organized as follows: 1M +---------------+ 0xFFFF \ \ | System BIOS | | | | ROM and | | | | FDC ROM | | | 960K +---------------+ 0xF000 | | | Option ROM, | | | | PnP BIOS ROM | | | | & Option RAM | | | 816K +---------------+ 0xCC00 | High RAM | | HDC BIOS RAM | | 384 KB | 800K +---------------+ 0xC800 | [640K - 1M] | | Video BIOS | | A000 - FFFF | | ROM, Option | | | Conventional RAM | ROM and RAM | | | 1 MB 768K +---------------+ 0xC000 | | [0K - 1M] | Video RAM: | | | 0000 - FFFF | VGA color | | | | and | | | | monochrome | / | 640K +---------------+ 0xA000 \ | | | | | | Base | | | | System | | Low (DOS) RAM | | RAM | | 640 KB | | | | [0K - 640K] | 1K +---------------+ 0x0100 | 0000 - 0FFF | | IV and BDA | | | 0K +---------------+ 0x0000 / / The MS-DOS Conventional memory map from 0 KiloBytes up to 1 MegaByte [1 MB]: Module Name and Usage Range Size -------------------------------------------------------------------------------------- * Low (DOS) RAM: 0K - 640K 640 KB - Interrupt Vectors (IV) and BIOS Data Area (BDA) 0K - 1K 1 KB - Base System RAM 1K - 640K 639 KB * High RAM: 640K - 1M 384 KB - Video RAM (VGA color and monochrome) 640K - 768K 128 KB - Video BIOS ROM, Option ROM and Option RAM 768K - 800K 32 KB - Hard Drive Controller (HDC) BIOS RAM 800K - 816K 16 KB - Option ROM, Plug-and-Play (PnP) BIOS ROM and Option RAM 816K - 960K 144 KB - System BIOS ROM and Floppy Drive Controller (FDC) ROM 960K - 1M 64 KB * TOTAL Conventional RAM 0K - 1M 1 MB The physical RAM below 640K is used by MS-DOS as its resource (mapped as shown above). Some of the memory above 640K is used for Video RAM, because various video types (CGA, EGA, MGA, PGA, 8514, VGA) have different requirements and starting locations, depending also on video controller bus types (ISA, VLB, PCI, AGP) and chipset brand/model (Tseng Labs, Cirrus, Trident, 3Dlabs, Number Nine, S3, Matrox, ATI, NVidia, 3dfx etc). But MS-DOS can map the unused "chunks" of remaining RAM immediately above the 640K barrier (the 384 KB "High RAM" area), if the BIOS "tells" it to at boot time. That's why this region is also called the Upper Memory Area (UMA), and it can be used to load programs, drivers, TSRs (Terminate and Stay Resident programs), and even parts of DOS itself "high", thus freeing more conventional RAM. This is possible by mapping the Upper Memory Blocks (UMBs) into usable RAM, by upper/extended/expanded memory managers, like the MS HIMEM.SYS and MS EMM386.EXE "combo", bundled with all Microsoft OSes/Environments, that load from the CONFIG.SYS file at bootup. 2. Extended and Expanded Memory [above the 1st MegaByte] A. Extended Memory ["longer"] Extended memory is an intrinsic part of the Intel CPU (X86) architecture. It is addressed directly in the CPU memory address space, above the 1st MegaByte on all IBM PC compatibles. MS-DOS (still) assumes that it runs on a 8088 CPU, and can thus only address the first 1 MegaByte [1024 KiloBytes] of memory space. :( Newer CPUs starting with the 80286 are capable of addressing the memory above the 1st Meg. But normally this memory canNOT be accessed by processors in "Real Mode" (designed for compatibility with the old 8088), using a single-tasking "Real Mode" Operating System, like Microsoft MS-DOS. Thus newer DOS based programs and games are designed to use a "Protected Mode" run-time environment ("DOS extender" using the DPMI interface) to access up to 32 MegaBytes of extended memory for intensive graphics rendering (SVGA modes), 3D textures and video/animation playback. Examples: Eidos Tomb Raider I, Lucas Arts Rebel Assault I and II, 3D Realms DukeNukem 3D. Other programs like RAM disks (MS RAMDRIVE.SYS), print spoolers, disk caches (MS SMARTDRV.EXE), use a ROM BIOS feature (on newer PCs that support it) that allows them to copy data between conventional and extended memory. Although these programs cannot execute in extended memory, they can use it as storage space. To access the entire physical extended memory on X86 compatible PCs, software programs need to perform in "Protected Mode" (also called "386 Enhanced Mode") by loading special (virtual I/O) drivers, thus allowing multi-tasking and faster (32-bit) I/O access, like Microsoft Windows in all its newer incarnations. Another processor mode is the "Virtual Real Mode", which allows "Real Mode" DOS programs to execute from within a "Protected Mode" environment in a confined (isolated) DOS session/box, by emulating a "Virtual Machine" (VM), and used by "Protected Mode" OSes/Environments, like Microsoft Windows. The first 64 KB of contiguous memory space located above the 1st Meg [between 10000 - 10FFF] is referred to as the High Memory Area (HMA), and is addressable within by MS-DOS as a result of the segmented memory scheme used to allow X86 CPUs to address more than 64 KB of RAM. Begining with MS-DOS 5.00 a large portion of the MS-DOS resident module (i.e. DOS BUFFERS) and/or some DOS Mouse drivers are stored in the HMA. MS-DOS canNOT load in the HMA if it is already occupied by another resident program at bootup. Extended memory can be used according to the XMS (eXtended Memory Specification) 3.0 standard, defined jointly by Microsoft, Intel, Lotus and AST, if mapped by an XMS device driver like HIMEM.SYS, provided with all Microsoft OSes/Environments. The XMS 3.0 standard allows the extended memory to be used by software designed to take advantage of it: - Terminate and Stay Resident (TSR) programs like DOS MOUSE Drivers; - Extended Memory Specification (XMS) applications like MS Windows; - XMS DOS games like 3D Realms DukeNukem 3D; - Static or dynamic RAM disks like MS RAMDRIVE.SYS; - Disk caching software like MS SMARTDRV.EXE; - Expanded Memory Specification (EMS) implementation like MS EMM386.EXE enhanced upper/extended/expanded memory manager, which uses page mapping (on 80386 and newer CPUs) to convert extended RAM into expanded, thus freeing additional conventional memory for use by MS-DOS and DOS programs. B. Expanded Memory ["fatter"] Expanded memory is defined within the architecture of the IBM PC/AT standard. It is refered to as "Paged Memory", can be addressed through a Page Frame within the first 1 MegaByte [1024 KiloBytes], and is thus accessible on all compatible 80X86 CPUs begining with the 8088 and including 80286, 80386, 80486, Pentium, Pentium Pro, Pentium II, Pentium III etc. The Lotus-Intel-Microsoft (LIM) 4.0 agreement is currently recognized as the common Expanded Memory Specification (EMS) industry standard. LIM 4.0 describes the following memory architecture: PC (X86) MAIN MEMORY LIM EXPANDED MEMORY 16M/4T +---------------+ | Extended | | Memory (XMS) | . up to 16 MB . +---------------+ 32M . on a 80286, . /| | . 4 GB on a . // | | . 80386/80486, . / / | | . 4 TB on a . / / | | | 80586/80686 | / / | | | etc... | / / | | 1M +---------------+ / / | | | High RAM |/ / | | 960K +---------------+ / | | | High Page | / | | | Frame: 12 | / | | | 16K Physical | / | | | Pages | / . Expanded . 768K +---------------+ / . Memory (EMS) . | High RAM |/ . divided into . 640K +---------------+\ . 16K Logical . | Low Page | \ . Pages . | Frame: 24 | \ | | | 16K Physical | \ | | | Pages | \ | | | | \ | | 256K +---------------+ \ | | | |\ \ | | | Low RAM | \ \ | | | | \ \ | | 0 +---------------+ \ \ | | \ \ | | \ \ | | \\ | | \| | +---------------+ 0 The Expanded Memory Standard (EMS) allows up to 32 MegaBytes of memory to be mapped into a total of 36 16K pages (as shown above) by swapping ("bank switching") small blocks ("pages") of extra memory into the 1M address space, so that only a few pages are addressable at a time, if using an expanded memory manager like Microsoft's EMM386.EXE. Third party enhanced memory managers like Quarterdeck's QEMM386.SYS (begining with version 7.0) can map and use up to 64 MegaBytes as expanded memory. The Page Frame below the 640K mark loads in a 64K contiguous low (DOS) RAM region, and allows the existing RAM to be shadowed, usually reserved for use by Operating Systems/Environments, like MS Windows. The Page Frame above the 640K barrier occupies a 64K contiguous high RAM region in the Video RAM and ROM areas, and is designed for DOS apps/games usage. Program code can be run or data can be stored interchangeably in any of these frames. Software using LIM 4.0 standard can thus have a large amount of physical memory available, but must access it by manually switching pages as required. LIM 4.0 can be implemented as a software emulation by a device driver, using the eXtended Memory Standard (XMS) in "Virtual X86 Mode" on any 80X86 CPU, so that the memory is mapped into any of the physical LIM pages. MS-DOS and MS Windows recognize LIM 4.0's presence and allow MS MSCDEX, MS SMARTDRV and other devices/drivers/TSRs to be allocated ("loaded") into LIM pages. LIM is not integrated into the Operating System though. To be able to map EMS, MS-DOS and MS Windows emulate LIM 4.0 using the computer's physical extended memory (XMS). This is achieved by a software control program called EMS device driver, which loads from the CONFIG.SYS file upon bootup on all X86 compatible PCs, like MS EMM386.EXE provided with all Microsoft OSes/Environments. DOS programs: - RAM disks like MS RAMDRIVE.SYS; - Disk caching routines like MS SMARTDRV.EXE; - CD-ROM driver extensions like MS MSCDEX.EXE; - EMS programs/games like Lucas Arts X-Wing etc, can be configured to use extended and/or expanded memory under the LIM 4.0 standards, as needed. See "BASIC *ESSENTIAL* MEMORY TIPS" in MEMORY.TXT (included) for a list of DOS applications, utilities and games that use EMS. II. MS-DOS UPPER MEMORY REGIONS + MAPPING Dale F. Ogden, computer programmer, was very kind to send me this detailed answer to my questions about MS-DOS upper memory regions mapping. My most sincere *THANKS* go to Dale for his valuable contribution to these files! "Greetings: Beyond the first 640K of conventional memory (0000h to 9FFFh), in the Upper Memory Areas, there are various types of information stored in ROM BIOS that depend upon the type of installed hardware. There are also areas reserved by the system for specific purposes (all memory addresses are in hexadecimal notation): - A000 to AFFF: VGA graphics. - B000 to B7FF: monochrome text (this region is usually available for loading TSRs and drivers "high" into UMBs). - B800 to BFFF: VGA Text. - C000 to C7FF: accelerated video cards. - C800 to EFFF: much of this region is available to create the page frame for EMS memory or to load TSR programs and drivers. Somewhere in that region there is ROM for the hard drives and likely for other hardware, too. - F000 to FFFF: usually cluttered with ROM (the floppies use this area) and most is not available for loading stuff; however, some of this area may be available. - 10000 to 10FFF: the first 64K beyond 1MB is referred to as the High Memory Area (HMA) that is addressable within by DOS as a result of the segmented memory scheme used to allow a 16-bit processor to address more than 64 kilobytes of memory (2^16=64K). Starting with MS-DOS 5.0, a large portion of the MS-DOS resident module is stored in the HMA, including, in some cases, Microsoft mouse drivers. - Beyond that is extended memory which, since the '386, can be "mapped" to whatever you want it to be. Memory managers, like EMM386, QEMM386, RM386, use command line parameters to load TSRs and drivers into specific regions of upper memory. These regions are defined not by specific addresses, but by available contiguous regions. The region B000 to B7FF (32K) is the first available region or UMB (Upper Memory Block) on my system. From CB00 to DBFF (68K) is the second available region and the EMS page frame is stored from DC00 to EBFF (64K). Each system is likely to be somewhat different. HiMem.Sys is the most conservative of all the memory managers in that it uses only areas not needed by anything else. Third party memory managers usually are more aggressive (but almost infinitely configurable) and recover memory used by ROMs that might only be needed at BOOT. In addition, certain technologies developed by the vendors of 3rd party memory managers (QEMM's "Stealth" and NetRoom's "Cloaking"), allow the Upper Memory Area (UMA) to be used for multiple purposes, but of course, not at the same time. The memory manager controls which function has access to the memory at any particular time and swaps the other information to extended (XMS) or expanded (EMS) memory (if available). The regions are not defined by any particular addresses. When DOS loads something in upper memory, it looks for available UMBs. Without a switch (/L:n, where usually n=1-4), it would load it into the first available UMB. The /L:n switch causes it to load in the designated available UMB. The purpose of this is to efficiently use the memory. TSRs and Drivers usually must be loaded into contiguous blocks of memory, so you want to load larger TSRs into larger UMBs and smaller TSRs into smaller UMBs. The actual addresses of those upper memory regions depend upon your system. The utilities that come with QEMM (Manifest) and other 3rd party utilities are more useful than MSD and make it easier to analyze what is happening with memory. The documentation that comes with QEMM is as good as any textbook in describing what is going on with conventional and extended memory, UMBs, HMA, EMS, XMS, VCPI and DPMI. There are also articles about optimizing memory usage in the MicroSoft Knowledge Base (MSKB): http://support.microsoft.com/support/ If your goal is to maximize conventional memory (you now have 623K which seems adequate for almost any purpose, I've never seen anything to need more than 619K to run, and 634K is the maximum possible with a VGA video card), invest in QEMM, but that seems a high price to pay for potentially only 11K of RAM. Hope I've been helpful. Dale F. Ogden" III. MY ADDENDUM ON UPPER MEMORY REGIONS MANAGEMENT To exemplify the Upper Memory Regions (UMRs) on a PC/AT IBM (X86) compatible computer, I have pasted below my system's MSD (the DOS based MicroSoft Diagnostics tool) Upper Memory Area (UMA) chart: ------------------------------- Memory ----------------------------- Legend: Available " " RAM "##" ROM "RR" Possibly Available ".." EMS Page Frame "PP" Used UMBs "UU" Free UMBs "FF" 1024K FC00 RRRRRRRRRRRRRRRR FFFF Conventional Memory F800 RRRRRRRRRRRRRRRR FBFF Total: 640K F400 RRRRRRRRRRRRRRRR F7FF Available: 625K 960K F000 RRRRRRRRRRRRRRRR F3FF 640864 bytes EC00 FFFFFFFFFFFFFFFF EFFF E800 UUUUUUUUUUUUUUFF EBFF Extended Memory E400 UUUUUUUUUUUUUUUU E7FF Total: 64512K 896K E000 UUUUUUUUUUUUUUUU E3FF DC00 UUUUUUUUUUUUUUUU DFFF MS-DOS Upper Memory Blocks D800 UUUUUUUUUUUUUUUU DBFF Total UMBs: 122K D400 PPPPPPPPPPPPPPPP D7FF Total Free UMBs: 17K 832K D000 PPPPPPPPPPPPPPPP D3FF Largest Free Block: 17K CC00 PPPPPPPPPPPPPPPP CFFF C800 PPPPPPPPPPPPPPPP CBFF Expanded Memory (EMS) C400 RRRRRRRRRRRRRRRR C7FF LIM Version: 4.00 768K C000 RRRRRRRRRRRRRRRR C3FF Page Frame Address: C800H BC00 ################ BFFF Total: 33152K B800 ################ BBFF Available: 32720K B400 UUUUUUUUUUUUUUUF B7FF 704K B000 UUUUUUUUUUUUUUUU B3FF XMS Information AC00 AFFF XMS Version: 3.00 A800 ABFF Driver Version: 3.5f A400 A7FF A20 Address Line: Enabled 640K A000 A3FF High Memory Area: In use Available: 65535K Largest Free Block: 65535K Available SXMS: 214976K Largest Free SXMS: 214976K VCPI Information VCPI Detected: Yes Version: 1.00 Available Memory: 32720K To display this chart on your system, run: MSD from a DOS prompt, and then press M. See MSD95.TXT (part of W95-11D.ZIP) or MSD62.TXT (part of W31-11D.ZIP) for MSD details. The UMA is contained between memory addresses A000 - FFFF on all X86 Intel compatible PCs (see chart above). As you can see in this particular layout, the entire UMA is mapped into two regions of available Upper Memory Blocks (UMBs): - region 1: located between addresses B000 - B7FF, enabled by the I=B000-B7FF EMM386.EXE switch (see further below), and - region 2: located between addresses C800 - EFFF, enabled by the I=C800-EFFF EMM386.EXE switch (see further below). These two UMRs are available for loading devices, drivers and/or TSR (Terminate and Stay Resident) programs "high", using the CONFIG.SYS DEVICEHIGH and INSTALLHIGH, and the AUTOEXEC.BAT LOADHIGH (abbreviated as LH) commands. Such an UMA layout can be obtained ONLY by using an Upper/Extended/Expanded memory manager in CONFIG.SYS, like Microsoft's HIMEM.SYS + EMM386.EXE "combo", or a similar 3rd party enhanced memory manager, such as Quarterdeck's QEMM386.SYS, Helix's NetRoom RM386.EXE, Qualitas' 386MAX.SYS, Caldera's DR-DOS EMM386.EXE, Uwe Sieber's UMBPCI.SYS etc, to map the UMA, and to provide UMBs that allow drivers/devices/TSRs to load "high" and programs to use it. Example: DEVICE=drive:\path\HIMEM.SYS /TESTMEM:OFF DEVICE=drive:\path\EMM386.EXE RAM I=C800-EFFF I=B000-B7FF M3 AUTO The above UMA layout corresponds to these EMM386.EXE two I=xxxx-yyyy switches. The Legend explains the meaning of the symbols. The areas marked with ## and RR canNOT be mapped by memory managers, because they are used by Extended, Hard Disk, Option and/or Video BIOS ROM and RAM. The 64K contiguous area marked with PP (between C800 - D7FF in this case) is occupied by EMM386.EXE's Page Frame, in expanded memory "mode", enabled by the RAM or HIGHSCAN EMM386.EXE parameters. The areas marked with UU (in region 1 and 2) are taken by devices, drivers and/or TSRs, ONLY if loaded with DEVICEHIGH in CONFIG.SYS, or LOADHIGH (LH for short) in AUTOEXEC.BAT. The FF areas represent free UMBs, and can be used by programs specifically written to make use of the UMA, like MS Windows. NOTE: The EMM386.EXE line MUST FOLLOW the HIMEM.SYS line in CONFIG.SYS! ALL OTHER DEVICE/DEVICEHIGH commands MUST FOLLOW the HIMEM.SYS and EMM386.EXE lines in CONFIG.SYS! The "n" variable (used by the "/L:n" switch) can have any integer value begining with 1 and up to the maximum number of UMRs available on your machine, as mapped by an Upper/Extended/Expanded memory manager (EMM386.EXE, QEMM386.SYS, RM386.EXE, 386MAX.SYS, UMBPCI.SYS etc) loaded from CONFIG.SYS. You can fiddle with the "/L:1", "/L:2"... "/L:n" etc switches to determine your best UMA setup. Example of CONFIG.SYS DEVICEHIGH line that uses a specific /L:n switch to load a particular device/driver/TSR into a targeted UMR: [CONFIG.SYS lines are processed before AUTOEXEC.BAT lines when your machine boots] DEVICEHIGH /L:1=C:\path\IFSHLP.SYS This line loads IFSHLP.SYS, the mandatory Windows/WfWG 3.xx/9x 32-bit disk access compatibility (legacy) DOS driver in the UMA region 1, located in this example between addresses B000 - B7FF. The B000 - B7FF UMR is not used by the standard PC/AT computer BIOS or Microsoft based OSes if you don't use two video adapters in the same PC, or an older black and white (monochrome) video controller. Therefore you can gain an extra 32 KB of contiguous upper memory available to programs/TSRs, ONLY IF you add the I=B000-B7FF switch to your memory manager line in CONFIG.SYS (see the EMM386.EXE line above). Same /L:n switches can also be used with the LOADHIGH (abbreviated as LH) command in AUTOEXEC.BAT, to load MS-DOS mode TSRs/drivers at bootup. An example is loading the DOS Mouse driver in UMA region 1: [AUTOEXEC.BAT lines are processed after CONFIG.SYS lines when your machine boots] LOADHIGH /L:1=C:\path\MOUSE <YOUR_MOUSE_DRIVER_PARAMETERS> The order of loading devices/drivers/TSRs in Upper Memory is of UTMOST importance: larger FIRST, smaller LAST. You need to experiment with multiple configurations until you reach your optimum memory setup, eventually loading ALL your devices/drivers/TSRs in UMA, thus freeing maximum possible low DOS memory, which is better used by DOS based programs/games. Have fun!