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====================================================================== INTRODUCTION ====================================================================== A new angle on memory management Version 3.00 of Microsoft Windows brings a new angle to PC memory management. It provides a protected mode graphical operating environment that runs existing DOS applications and allows Windows applications to break the 640K barrier. Windows 3.00 memory management is simpler in many ways than that of previous versions. However, its flexibility continues to present a challenge to those who want to understand its operation in depth. This document examines the three types of memory that Windows 3.00 can use (conventional, extended, and expanded) and discusses how the three modes of Windows 3.00 (real, standard, and enhanced) operate and use memory. ====================================================================== MEMORY TYPES ====================================================================== There are three different kinds of memory that can be installed in your machine. These are conventional, extended, and expanded. In addition, IBM PC-compatible machines contain a 384K reserved I/O address space. CONVENTIONAL MEMORY =================== Conventional memory is the first 640K of memory in your machine (see Figure 1). DOS has a limit of 640K of addressable memory, and all DOS applications have to run within this conventional memory. All of the Windows 3.00 operating modes share this limitation for running DOS applications, but standard and enhanced modes break the 640K limitation for running Windows applications. Windows 3.00 enhanced mode can create multiple virtual DOS machines (for more information on virtual DOS machines, see the "Enhanced Mode and Conventional Memory" section of this application note). NOTE: Enhanced mode Windows 3.00 also allows DOS applications to break the 640K barrier if they are written to use the Microsoft DOS Protected Mode Interface (DPMI) specification. DPMI allows DOS applications to run in protected mode under Windows 3.00, using up to 16 megabytes of extended memory directly. Applications must be specifically written for DPMI to provide this feature. ************************************************** Figure 1: Conventional and Extended Memory Graphic not available in text-formatted file. Please see printed document for Figure 1. ************************************************** 384K RESERVED I/O ADDRESS SPACE =============================== Between the top of conventional memory at 640K and the start of extended memory at 1024K lies the 384K reserved I/O address space (see Figure 2). This area does not contain physical memory. Mapped into the 384K reserved I/O address space are the BIOS (basic input/output system) ROM chips and the display adapter memory. When you install other accessory cards, such as network adapters, they occupy space within the 384K reserved I/O address space as well. It is important to remember that the 384K reserved I/O address area is always located in the same area of the IBM PC-compatible computer's address space: from 640K to 1024K (A000 to FFFF hexadecimal). There are no exceptions to this rule. This means that a standard IBM-compatible machine with 640K of conventional memory installed really has 1 megabyte of address space. The system memory occupies the first 640K, and the 384K reserved I/O address space occupies the area from 640K to 1 megabyte. This does not mean that the machine has 1 megabyte of memory. A machine with 1 megabyte of physical memory has an address space of 1408K. This consists of the 640K conventional memory, the 384K reserved I/O address space, and the 384K of extended memory starting at 1024K. The IBM PS/2 Models 50, 50Z, and 60 are examples of machines that always ship with at least 1 megabyte of memory installed. EXTENDED MEMORY =============== Extended memory is the simplest type of add-on memory to understand (see Figure 1). It is also the type of memory used by Windows 3.00 running in standard or enhanced operating mode. Extended memory is simply a seamless continuation of the original 1 megabyte address space on 80286 and 80386 computers. Extended memory always starts exactly at 1024K, where the 384K reserved I/O address space ends. There are no exceptions. It is not possible for an 8086 or 8088 machine to have extended memory. This is a hardware limitation of the 8086/8088 processors, which can handle only 1024K of total address space (that is, 640K system memory plus 384K reserved I/O address space). The 80286 processor can address 16 megabytes of total memory and the 80386 processor can address up to 4 gigabytes. Note that PC manufacturers often refer to extended memory as expansion memory, which is not to be confused with expanded memory. Windows 3.00 and all applications running under Windows access extended memory via the Microsoft eXtended Memory Specification (XMS). Rather than accessing extended memory directly, access is made via an XMS driver. This driver is called HIMEM.SYS. Older DOS applications that check available extended memory via the interrupt 15 service 88H will not see any extended memory with an XMS driver loaded. These applications must use the XMS, instead of interrupt 15, to access extended memory. EXPANDED MEMORY =============== Older versions of Windows use mostly expanded memory. Today, Windows 3.00 uses expanded memory only when running in real mode. However, it is important to understand the concept of expanded memory if you still run DOS applications that use it. There are two different kinds of expanded memory, differentiated by their Lotus/Intel/Microsoft (LIM) Expanded Memory Specification (EMS) version number. LIM 3.2 Expanded Memory ----------------------- We discussed earlier that the old PC/XT machines with 8086/8088 processors can address only 640K of memory. You can't add more than 640K of standard memory to the system, but you can provide more than 640K through a technique called bank switching. Expanded memory uses an empty area in the 384K reserved I/O address space of the machine to provide this functionality. Figure 3 shows the memory addressing range of an 8088-family processor on the left and an expanded memory card on the right. To use an expanded memory card, you must load a device driver to let the card know how to communicate with the PC. This device driver is called an Expanded Memory Manager, or EMM. The LIM 3.2 EMM establishes a 64K page frame within the 384K reserved I/O address space to perform EMS bank switching. The 64K page frame consists of four 16K contiguous pages. LIM 3.2 expanded memory won't work without a 64K contiguous page frame. The page frame is the area where the expanded memory manager maps information into and out of the RAM of the expanded memory card. Information is not physically copied from the EMS card to the RAM of the computer. The device driver simply changes the card's page registers to make the page frame point to the data on the expanded memory card. The data then appears in the page frame, and your application can access it. ************************************************** Figure 2: The 384K Reserved I/O Address Space (Use this page for reference when troubleshooting memory address conflicts.) Graphic not available in text-formatted file. Please see printed document for Figure 2. ************************************************** ************************************************** Figure 3: LIM 3.2 Expanded Memory Graphic not available in text-formatted file. Please see printed document for Figure 3. ************************************************** LIM 4.0 Expanded Memory ----------------------- The LIM 3.2 standard is fine for storing data such as spreadsheets in expanded memory, but it does not help for multitasking. This is why Lotus, Intel, and Microsoft created the LIM 4.0 standard. Comparing Figures 3 and 4 shows two of the major differences between LIM 3.2 and 4.0. First, you can have more than four 16K pages, much more. LIM 4.0 supports up to 64 pages, which are enough to bank 1 megabyte of memory at once. Second, the page frame itself no longer has to be four contiguous 16K pages. In fact, you need no page frame at all. Whichever EMS version you are dealing with, the basic operating principle of bank switching is still at work. Backfilling ----------- With LIM 4.0's limit of 64 16K pages, you have enough pages to bank switch the entire conventional address range of the processor. Yet there must be no active ROM or RAM of any sort where you put an expanded memory page. This means you can't map EMS pages on top of anything that is already occupying address space in your machine (such as loaded DOS or video/system ROM). On the 80286 processor, this means you should disable as much motherboard memory as possible (down to 256K) and let the expanded memory card supply that memory. This process is called backfilling. This doesn't mean that your computer will have only 256K -- your programs still see a 640K machine. But since the expanded memory card is now supplying the memory, it can bank switch the memory. This capability is called (erroneously) "large page frame." The 80386 processor has a built-in ability to readdress any page of memory to any other location. This means you don't have to backfill on an 80386 to get large page frame LIM 4.0 functionality, nor do you need an expanded memory board. It's easy to convert your 80386's extended memory to expanded with an 80386 Expanded Memory Manager such as Microsoft EMM386.SYS. If you're using an expanded memory board on an 80386 machine, read your manual carefully before you backfill. Not all memory boards have the register support to supply more than four 16K pages (LIM 3.2). Though a memory driver may conform to the LIM 4.0 specification, that does not mean the hardware can provide more than four pages. Also, since Windows 3.00 supports extended memory directly, backfilling expanded memory will not give you any advantages unless you plan to run only real mode Windows. ************************************************** Figure 4: LIM 4.0 Expanded Memory Graphic not available in text-formatted file. Please see printed document for Figure 4. ************************************************** LIMulators ---------- There are some programs available that emulate expanded memory using extended memory and/or hard disk space. These programs are sometimes known as LIMulators. They are not much of an advantage because although they supply expanded memory, they are not hardware. They must place a 64K EMS page frame in conventional memory and also take up space for the driver itself. LIMulators generally take upward of 80K conventional memory to run. Since conventional memory is the most precious memory on your machine, we do not recommend these types of programs. They are also extremely slow. Expanded Memory Difficulties ---------------------------- Expanded memory requires a page frame to work, and the page frame is located within the 384K reserved I/O address space of your machine. Unfortunately, your EMM is not the only competitor for that memory space. Add-on boards such as network cards, 3270 emulation cards, ESDI disk controllers, and others can contend for this address space. Several potential difficulties can arise due to this contention: 1. Lack of Space The major problem is simply finding at least 64K of contiguous free space in which to place the page frame. LIM 4.0 does not require a 64K page frame but is almost useless without it. Frequently the address areas of various adapter cards need to be shuffled about to open a contiguous 64K page frame. Complicating this process are such boards as the IBM 3270, which have nonmovable addresses in most machines. 2. Mapping Conflicts Most EMMs (such as EMM386.SYS and Windows 3.00 enhanced mode) use a search algorithm to find unused memory between C000 and DFFF located in the 384K reserved I/O address space to use as page frames. Some cards (adapters) do not reserve their address space until you access the card, so the memory manager can inadvertently map EMS pages on top of an address the card will request. This can cause hanging and intermittent operation. This problem is fairly rare because the page search routine can locate almost all popular adapters. In case of problems, the first thing to do is to disable expanded memory. This will show if a page conflict really is causing the symptom you are experiencing. If the problem goes away without expanded memory, the memory manager must be told to exclude the address the adapter is occupying from consideration as a page location. The adapter also may have to be moved. You do this different ways with different memory managers. Consult your memory manager's documentation for information on how to exclude an address range. ====================================================================== WINDOWS 3.00 MODES AND MEMORY USAGE ====================================================================== How it works in each mode This section examines how the three different modes of Windows 3.00 (real, standard, and enhanced) use the different types of memory we have discussed (conventional memory, the 384K reserved I/O address space, extended memory, and expanded memory). REAL MODE WINDOWS 3.00 ====================== Real Mode and Conventional Memory --------------------------------- Windows 3.00 in real mode is similar in most respects to Windows/286 versions 2.x. Real mode Windows 3.00 executes entirely within conventional memory. It requires 384K of free conventional memory (393,216 bytes reported by CHKDSK) to start up successfully. Real Mode and the 384K Reserved I/O Address Space ------------------------------------------------- Windows 3.00 does not access the 384K reserved I/O address space directly in real mode. Remember though, if an external EMM is present (such as EMM386.SYS), the EMM will use areas of the 384K reserved I/O address space. NOTE: Windows 3.00 real mode operation is similar in most respects to Windows/286 versions 2.x. Real mode can use most Windows 2.x device drivers and runs applications written for Windows 2.x. Real Mode and Expanded Memory ----------------------------- SMALL VERSUS LARGE PAGE FRAME MODE Real mode Windows 3.00 will automatically switch into large page frame mode when 280K (plus or minus 8K) of free, mappable expanded memory pages in conventional memory are available after all Windows code has been loaded. The ending position of Windows code in memory plus the amount of Windows global memory determine the start of free expanded memory pages. Global memory is a memory segment that Windows puts aside to store things that need to be globally available to all applications, such as printer drivers and fonts. The point at which the free mappable expanded memory pages begin is called the EMS line. ADJUSTING THE EMS LINE There is no way to set the position of the EMS line explicitly, because real mode Windows sets it automatically, as discussed above. However, you can adjust the EMS line position in a manner relative to its current position with the command line parameters discussed below. REAL MODE WINDOWS EXPANDED MEMORY COMMAND-LINE PARAMETERS The /N Switch Starting real mode Windows with the /N command-line switch disables real mode Windows' use of expanded memory for banking of Windows applications. This effectively eliminates an EMS line. The /N switch does not disable expanded memory but only real mode Windows' use of it. Your external EMM will still be present. A page frame will be established, and applications can still use LIM 3.2 (if a 64K contiguous page frame is present). This means that this switch is not useful for debugging possible expanded memory page frame conflicts. The /N switch disables only real mode Windows' use of expanded memory, not the expanded memory itself. To disable the expanded memory itself, you must remove the external EMM. The /L Switch Starting real mode Windows with the /L+nnn parameter moves the EMS line up or down the specified amount of kilobytes (rounded to 16K increments). The command line WIN/L+16 moves the EMS up 16K, possibly fine-tuning Windows with your system, provided you are already in large page frame. Do not use the /L-16 parameter to move the EMS down, as it will infringe on global memory and cause problems with printing or displaying fonts. Real mode Windows normally starts in large page frame. Start real mode Windows with WIN /L+200 (where 200 is simply an arbitrarily large number) to force real mode Windows to small page frame mode. There is almost never a practical use for any other positive parameter. The /E Switch The /Ennn parameter gives you the ability to adjust the 280K default point at which real mode Windows will go into large page frame mode (see above). Keep in mind that real mode Windows does not automatically use one mode or the other without a good reason. Explicitly setting small or large page frame mode, as opposed to Windows' automatic choice, may cause problems. Windows' automatic choice is usually the best choice to take. However, if you want to explicitly set one mode or the other, you can use this switch. For example, starting real mode Windows with WIN /E100 causes Windows to go into large page frame mode if only 100K of bankable conventional EMS pages are free after Windows code initialization (this effectively switches real mode Windows to large page frame mode). Conversely, starting real mode Windows with WIN /E600 forces small page frame mode in all circumstances. You should normally use the /L+200 switch for this purpose. Real Mode and Extended Memory ----------------------------- CODE CACHING USING EXTENDED MEMORY Real mode Windows 3.00 does not access extended memory directly. However, if extended memory is present and HIMEM.SYS is loaded, real mode Windows can speed its operation considerably by performing code caching to extended memory. All Windows applications are segmented, that is, divided into segments that have certain attributes. These attributes include movable attributes, which means that the segment can be moved around in memory, and discardable attributes, which means that the segment can be discarded (that is, forgotten about, overwritten, and reloaded from disk when necessary). The largest portion of a given Windows application has both the movable and discardable attributes. Under real mode Windows, a lot of discarding goes on because real mode is limited to conventional memory. Windows applications are frequently 600K or larger, much larger than available free memory on a 640K machine with real mode Windows loaded. A Windows application keeps a minimum amount of code loaded in memory; this is known as its swapsize. As the program executes and you choose various functions, whenever Windows runs out of memory, it discards part of the application and overwrites it with new code loaded from the executable file on the hard disk. If XMS memory is accessible to Windows 3.00 via HIMEM.SYS, Windows will effectively discard code to extended memory. Rather than forgetting about the code segment and overwriting it with new code from the executable file, Windows copies the code segment to extended memory. Then, instead of having to reload from the executable file, Windows can fetch the code from extended memory when it is required again. This feature speeds up real mode operation considerably; code caching is not present in Windows/286 versions 2.x. Note that this feature does not replace the Windows SMARTDrive disk caching utility. SMARTDrive should still be loaded whenever possible. USING XMS MEMORY IN DOS APPLICATIONS DOS applications that use XMS memory can also be run from real mode Windows if the required amount of XMS memory is specified in the PIF (Program Information File). One important point about running such applications is that real mode Windows is already using all of the available XMS memory for code caching. Therefore, to run a DOS application PIF that requires XMS memory, you must swap extended memory to disk. For example, assume your machine has 2048K of extended memory. You specify in the PIF that your DOS application requires 1024K of XMS. Real mode Windows is already using all 2 megabytes of extended memory. When you run the DOS application, the first megabyte of XMS memory is swapped to disk, and the DOS application is given access to that megabyte. When you alt+tab back to real mode Windows, the original 1024K of XMS memory is reloaded from disk. Since this process can be slow, you should not request any more XMS memory than is absolutely necessary to run your application. SWAPPING DOS APPLICATIONS TO EXTENDED MEMORY Real mode Windows 3.00 can also swap DOS applications to extended memory. To do this, create a virtual hard disk in extended memory with the RAMDRIVE.SYS driver. Then, set the swapdisk= line in the [nonwindowsapp] section of the SYSTEM.INI file to point to the drive letter that RAMDrive creates. Note that you must have a RAMDrive that is at least three times larger than the largest DOS application you want to use. Also, be advised that using extended memory to create the RAMDrive will reduce real mode Windows' extended memory code caching ability and make it run more slowly. Note: Windows/286 versions 2.x have the ability to swap DOS applications directly to expanded memory. Since expanded memory is rarely used under Windows 3.00, this capability was removed. If you want to swap DOS applications to expanded memory, set up a RAMDrive in expanded memory and swap to the RAMDrive. RUNNING PROTECTED MODE DOS APPLICATIONS Windows real mode allows DOS applications that use a DOS extender technology such as VCPI (Virtual Control Program Interface) to run in protected mode. Extended memory allocation for such applications must be made in the PIF. STANDARD MODE WINDOWS 3.00 ========================== Breaking the 640K barrier on 286 machines Standard Mode and Conventional Memory ------------------------------------- When standard mode Windows 3.00 is executed, it adds the amount of free conventional and extended memory and looks at the total amount as one contiguous block of memory. Conventional memory has no special meaning under standard mode, except when running DOS applications. Running real or standard mode Windows 3.00 has the same DOS application support, and DOS applications must run within conventional memory. Standard Mode and the 384K Reserved I/O Address Space ----------------------------------------------------- Windows 3.00 does not access the 384K reserved I/O address space directly in standard mode. Still, if a physical expanded memory board is present, the board's EMM will use areas of the 384K reserved I/O address space. If you suspect a 384K reserved I/O address space conflict is causing a problem, temporarily remove the external EMM for testing purposes. Standard Mode and Expanded Memory --------------------------------- Standard mode Windows 3.00 does not use expanded memory at all. DOS applications running under standard mode can access expanded memory only if a physical expanded memory board along with the appropriate memory manager is present in the machine. Compatible 386 Expanded Memory Managers such as EMM386.SYS can be loaded to provide expanded memory outside of Windows. However, 386 Expanded Memory Managers cannot be used to provide expanded memory to DOS applications running from standard mode Windows. The 386 Expanded Memory Manager will be disabled when standard mode loads. See the "Expanded Memory for DOS Applications" section of this application note for more information on using EMS with standard mode. Standard Mode and Extended Memory --------------------------------- Windows 3.00 standard mode can access extended memory directly. It adds the free conventional memory and free XMS extended memory. It then provides the total as memory for Windows applications to use (minus the memory required by standard mode Windows itself). Standard mode initially accesses extended memory through the XMS driver HIMEM.SYS. DOS applications that use XMS memory can also be run from standard mode Windows. Since standard and real mode Windows both use the same DOS application support, the same restrictions apply (see the "Real Mode and Extended Memory" section of this application note). ENHANCED MODE WINDOWS 3.00 ========================== Entering the world of virtual memory Enhanced Mode and Conventional Memory ------------------------------------- Windows 3.00 enhanced mode deals with conventional memory in much the same way as standard mode. When enhanced mode Windows 3.00 is executed, it adds the amount of free conventional and extended memory, but in addition, Windows 3.00 combines a virtual hard drive memory factor and looks at the total amount as one contiguous block of memory. Conventional memory has no special meaning under enhanced mode, except when running DOS applications. Enhanced mode runs DOS applications by creating virtual DOS machines up to 640K in gross size. Each virtual DOS machine inherits the environment that was present before Windows enhanced mode was executed. This means that every driver and TSR loaded before you run Windows is present and consumes memory in every subsequent virtual DOS machine. The net memory available within virtual DOS machines under enhanced mode is slightly less than the free memory at the DOS prompt before you start Windows. Enhanced Mode and the 384K Reserved I/O Address Space ----------------------------------------------------- Windows/386 versions 2.x use the 384K reserved I/O address space only to place the expanded memory page frame, and then to a maximum of only four 16K pages. Windows 3.00 enhanced mode uses the 384K reserved I/O address space for two purposes: 1) to place DOS protected mode application program interface (API) translation buffers, and 2) to place the expanded memory page frame (if required). Frequently, all of the free pages in the 384K reserved I/O address space are utilized by enhanced mode. API TRANSLATION BUFFERS IN THE 384K RESERVED I/O ADDRESS SPACE Although Windows 3.00 enhanced mode breaks the 640K barrier for Windows applications, it still runs on top of DOS. The copy of DOS upon which Windows is running can execute and access data only within conventional memory. The same restriction applies to network software or other drivers loaded before enhanced mode Windows. Enhanced mode allocates buffers in the 384K reserved I/O address space to translate DOS and network API calls from protected mode to real mode. Since the 384K reserved I/O address space is within the first megabyte of address space, it can be accessed by DOS in real mode. The translation buffers are used as a window through which applications executing in protected mode can pass information to and from DOS and the network. Ideally, there would be enough free space in the 384K reserved I/O address space to place both the translation buffers and the expanded memory page frame. Yet on many configurations there isn't enough room. This means you have to make a choice. Either the expanded memory page frame can be eliminated or the translation buffers can be allocated in conventional memory instead of in the 384K reserved I/O address space. If the translation buffers are allocated in conventional memory, they take up space in every virtual machine from Windows that you create. You will have less space in virtual machines to run DOS applications. The translation buffers can be allocated either in the 384K reserved I/O address space or in conventional memory, but never half-and-half. Fortunately, Windows 3.00 enhanced mode provides a method for specifying your preference. To do this, place the following switch in the [386ENH] section of the SYSTEM.INI: ReservePageFrame=Boolean If ReservePageFrame=true (the default), enhanced mode Windows allocates the page frame first and the translation buffers second. This makes it likely that the translation buffers will be forced into conventional memory but allows you to use expanded memory in DOS applications. If ReservePageFrame=false, the translation buffers are allocated first and the page frame second if there is still room. This setting gives you the most free memory within virtual machines, but you may not be able to use expanded memory in DOS applications. However, remember that Windows applications do not need expanded memory to function; only DOS applications that can utilize expanded memory will be affected. One important note: If you are using the EMM386.SYS driver, translation buffers are always placed in conventional memory. PAGE FRAME PLACEMENT IN THE 384K RESERVED I/O ADDRESS SPACE As noted in the expanded memory discussion earlier in this document, expanded memory support requires a page frame located in the 384K reserved I/O address space. With LIM 4.0 expanded memory, it is not necessary to have a 64K contiguous page frame in this area. It's not necessary to have a page frame at all in LIM 4.0. Still, if you want to use expanded memory in your DOS applications, you must have a 64K contiguous page frame. This is composed of four contiguous 16K pages in the 384K reserved I/O address space. On a typical IBM machine there are only eight free 16K pages in the 384K reserved I/O address space (refer to Figure 2). Four contiguous pages are required for expanded memory support in DOS applications, leaving only four other free pages. Other cards such as network adapters and ESDI hard disk controllers also need to occupy pages in the 384K reserved I/O address space. Frequently the combination of installed adapters can break up the free area in the 384K reserved I/O address space so there is no 64K contiguous area in which to place the page frame. In this case, you will not see any free expanded memory in your DOS applications running under Windows 3.00 enhanced mode. If you experience this problem, you may need to rearrange your adapter memory locations to get expanded memory support for DOS applications. This is easiest to do on machines using the Micro Channel Architecture (MCA) or Extended Industry Standard Architecture (EISA) bus standards. IBM Personal System/2 models 50 and above are equipped with the Micro Channel bus. The PS/2 machines allow you to change adapter memory locations simply by booting with the PS/2 Reference Disk and choosing Change Configuration. A similar procedure is available on most EISA bus machines such as the COMPAQ SYSTEMPRO and HP Vectra 486. Normal Industry Standard Architecture (ISA) bus machines such as the IBM AT and COMPAQ 386 may require you to open the case and flip DIP switches on the cards to change their memory addresses. Use Figure 2 as a handy worksheet when readdressing adapters to open a 64K page frame. If you want, you can disable expanded memory support entirely under Windows 3.00 enhanced mode by adding the NoEMMDriver=yes parameter in the [386ENH] section of the SYSTEM.INI file. CONTROLLING ENHANCED MODE 384K RESERVED I/O ADDRESS SPACE MAPPING In Windows/386 versions 2.x, the WIN.INI parameters EMMExclude= and EMMInclude= are used to control expanded memory page frame placement. These parameters are used under Windows 3.00 enhanced mode to control not only the expanded memory page frame but also the API translation buffer mapping. Under Windows 3.00 these switches begin with the letters EMM only for downward compatibility reasons. They no longer apply only to expanded memory. The EMMPageFrame= parameter still applies only to the expanded memory page frame. In Windows 3.00 these switches have been moved from the WIN.INI file to the [386ENH] section of the SYSTEM.INI. Windows/386 versions 2.x do not use the E000-EFFF area of the 384K reserved I/O address space unless specifically instructed. Windows 3.00 enhanced mode will use this segment unless the machine identifies itself as a PS/2. To explicitly exclude an area of the 384K reserved I/O address space from mapping by Windows 3.00 enhanced mode, use the EMMExclude= statement. The EMMExclude= parameter accepts a four- digit hexadecimal memory range, such as EMMExclude=E000-EFFF. Since there is no standard for hardware implementation of the E000-EFFF area, it is frequently necessary to exclude this range for enhanced mode to function properly. Most adapter cards are automatically detected and excluded by Windows 3.00 enhanced mode. If you suspect a problem with a 384K reserved I/O address space memory conflict, use EMMExclude=. There are very few uses for the EMMInclude= statement. Normally Windows 3.00 enhanced mode automatically uses all free pages in the 384K reserved I/O address space. Likewise, there are few uses for the EMMPageFrame= statement, since it controls only the expanded memory page frame and not the translation buffers. The Windows/386 2.x LastEMMSeg= parameter is not used by Windows 3.00. Enhanced Mode and Expanded Memory --------------------------------- Windows 3.00 enhanced mode does not use expanded memory itself. It can create expanded memory for use by DOS applications written to use expanded memory, such as Lotus 1-2-3. Expanded memory required by a DOS application can be specified in the Advanced section of the application's PIF. It is no longer necessary for Windows applications to use expanded memory because they can now access extended memory directly. The main issues for expanded memory under Windows 3.00 are page frame conflicts, as discussed above. Windows/386 versions 2.x provide large page frame expanded memory only for the Windows virtual machine. Windows 3.00 enhanced mode provides large page frame LIM 4.0 expanded memory in all virtual DOS machines. This is not currently useful for most DOS applications that use expanded memory. Most DOS applications use only the 64K page frame itself, not the additional bankable pages in conventional memory that large page frame LIM 4.0 supplies. However, this feature may be useful in the future. A compatible external 386 memory manager such as EMM386.SYS can be loaded to provide expanded memory for DOS applications running outside of Windows 3.00 enhanced mode. Note: EMM386.SYS is specifically designed to work in conjunction with Windows 3.00. This driver is not needed to have expanded memory available inside of Windows 3.00 and is actually turned off when Windows 3.00 enhanced mode is run. See the "Expanded Memory for DOS Applications" section of this application note for more information. Enhanced Mode and Extended Memory --------------------------------- Like standard mode, Windows 3.00 enhanced mode can access extended memory directly. It adds the free conventional memory and free XMS extended memory plus a virtual hard drive memory factor. It then provides the total as memory for Windows applications to use (minus the memory required by enhanced mode Windows itself). DOS applications that use XMS memory can also access XMS in virtual machines under enhanced mode Windows. The XMS memory supplied to DOS applications by Windows 3.00 enhanced mode can be virtualized. RUNNING PROTECTED MODE DOS APPLICATIONS Windows enhanced mode allows DOS applications to run in protected mode if they are written to use the Microsoft DOS Protected Mode Interface (DPMI) specification. NOTE: Enhanced mode uses the XMS to initially load itself and its drivers into extended memory before starting up. This is why enhanced mode requires the presence of HIMEM.SYS, the XMS device driver. Enhanced Mode and Virtual Memory -------------------------------- A VIRTUAL MEMORY CONCEPTUAL ANALYSIS Virtual memory gives you the ability to run more simultaneous programs than the amount of physical memory installed on your computer would normally allow. Virtual memory has been widely used for years in the world of mainframe computers and recently came to the IBM world with the introduction of the IBM/Microsoft OS/2 operating system, which is based on the 80286 processor. Windows 3.00 enhanced mode goes beyond the world of OS/2 to offer virtual memory using the special demand paging capabilities of the Intel 80386 processor. The best thing about virtual memory in Windows 3.00 enhanced mode is that programs do not need to be written specifically to take advantage of it. When you start Windows 3.00 enhanced mode and from the Help menu, choose Help About Program Manager, you will see that much more memory is available than is installed in your machine. Windows applications can use this extra memory without being written specially for it because Windows applications are device independent. They let Windows handle the memory management and simply ask Windows for memory allocations. With virtual memory, Windows applications keep asking for more memory, which Windows 3.00 enhanced mode is now able to deliver. If you have less memory, the application runs slower; if you have more memory, it runs faster; but it is almost always able to run. At any given moment during the execution of a program, some parts of its code and data are in physical memory; the rest is swapped to the hard disk. Whenever a reference is made to a memory address, if the information is currently in physical memory, it is used without program interruption. If the information isn't in physical memory, a page fault occurs. The Windows 3.00 enhanced mode virtual memory manager takes control. The required code or data is pulled into physical memory from the hard disk, and if necessary, some other information is swapped out. Pages are swapped out on a least recently used (LRU) basis. The page(s) that have not been accessed for the longest time are the first to be swapped out. All this swapping occurs without notice to the user, who sees only a little hard disk activity. Windows 3.00 enhanced mode virtual memory is a demand-paged system. This means that pages of data are brought into physical memory when they are referenced. A demand-paged system does not attempt to predict what pages will be required in the future. The enhanced mode virtual memory subsystem is implemented by the Windows 3.00 Virtual Memory Manager (VMM) along with the pageswap device. The VMM maintains the virtual memory page table. The page table lists which pages are currently in physical memory and which are swapped to disk. Because Windows 3.00 enhanced mode is a multitasking environment, the VMM page table also contains a list of which memory pages belong to which process. When the VMM needs a page that is not currently in physical memory, it calls the pageswap device. Pageswap allocates and deallocates virtual memory and maps pages into and out of physical memory. Some virtual memory systems rely on program segmentation to do their work. Windows applications are segmented. However, virtual memory under Windows 3.00 enhanced mode is not related to the segmentation of Windows applications. All memory, virtual and physical, is divided into 4K pages and the system is managed on this basis. Page mapping starts at 0 kilobytes and works up. There are two kinds of pages that can be allocated: physical pages and virtual pages. The amount of physical pages is simply the amount of physical memory in the machine divided by 4K. In contrast, memory allocated to an application is made up of virtual pages. At any given time, a virtual page can be in physical memory or swapped to the hard disk. As mentioned above, Windows 3.00 enhanced mode virtual memory management uses the least recently used (LRU) page replacement algorithm. The virtual page table contains flags for each page that indicate whether the page has been "accessed" and if the page is "dirty." Accessed means that a process has made a reference to the page since it was originally loaded. Dirty means that a write has been made to the page since it was loaded. Because a memory write qualifies as an access, the Dirty attribute implies the Accessed attribute. To illustrate, assume Windows 3.00 enhanced mode is out of physical memory space. A process requests additional memory. Windows has to decide which page(s) currently in physical memory it should swap to disk to fulfill the request. This decision is a three-step process: 1. The virtual memory manager scans the page table, looking for pages that have neither an Accessed nor a Dirty attribute. During the scanning process, it clears the Accessed attribute from all the pages. 2. If it can find enough pages meeting the not Accessed/not Dirty requirement, it fulfills the request. It swaps the pages to disk and gives the resulting free memory to the process. 3. If it can't find enough pages the first time through, it repeats the scan. Yet this time through, none of the pages has an Accessed attribute because it was cleared by the first scan. Theoretically, therefore, more pages will meet the requirements, and the request can be fulfilled. If the required pages are still not found by the second scan, Windows then swaps out the pages regardless of their attributes. The benefit of Windows 3.00 enhanced mode virtual memory support is the ability to run more programs than could be supported by actual physical memory. The drawbacks are the disk space requirement for the virtual memory swap file and a decrease in overall execution speed when swapping is required. However, it's better to be able to run a program slowly in a virtual memory system than not to be able to run it at all. VIRTUAL MEMORY PAGING FILE OPTIONS AND CONTROLS Windows 3.00 enhanced mode can use one of two types of virtual memory paging files, or swap files: temporary or permanent. Only one type of swap file can be used when running Windows 3.00. Do not attempt to create a swap file on a RAMDisk. Creating a swap file on a RAMDisk is a self-defeating pursuit -- you would be sacrificing physical memory to provide a place to create virtual memory to replace the physical memory you have used to create the RAMDisk. Windows 3.00 in 386 enhanced mode requires a minimum of approximately 1.5 megabytes of hard disk space free on the paging drive to provide virtual memory support with a temporary swap file. A temporary swap file is simply a normal DOS file created on the hard disk that can shrink and grow in size as necessary. The temporary swap file is called WIN386.SWP. It does not have a Hidden or System attribute and can be deleted at any time you are not currently running Windows, if necessary. It is normally deleted automatically when you exit Windows 3.00 enhanced mode. This temporary swap file is the default swap file that Windows 3.00 uses and is created automatically when Windows 3.00 is started. Temporary swap file location and size can be adjusted by inserting parameters in the [386ENH] section of the SYSTEM.INI file. The temporary swap file is always created in your Windows 3.00 directory unless you set the PagingDrive= parameter. If the PagingDrive= parameter is set (for example, PagingDrive=D:), the swap file will be created in the root directory of the specified drive. There is no way to specify a subdirectory for the temporary swap file location. Temporary swap file size is controlled by the MaxPagingFileSize= parameter. The size of the temporary swap file can also be limited in a different way by the use of the MinUserDiskSpace= parameter, which tells enhanced mode to leave the specified amount of disk space in kilobytes free when creating a temporary swap file. A permanent swap file occupies a contiguous section of your hard disk. Because it is contiguous, using a permanent swap file moderately improves the speed of the Windows 3.00 virtual memory system, and its access requires less overhead than a normal DOS file. The permanent swap file is a hidden file called 386SPART.PAR, which also has a System attribute. It is always placed in the root directory. Since the permanent swap file must be contiguous, you can't create a permanent swap file larger than the largest contiguous free segment of your hard disk. Permanent swap files are created and deleted with the Windows 3.00 SWAPFILE.EXE utility program. A SYSTEM.INI parameter is not used to point to the location of the permanent swap file. Instead, the Swapfile utility program creates a SPART.PAR file in your Windows 3.00 directory. Windows 3.00 enhanced mode reads the SPART.PAR file to find out where the permanent swap file is and how large it is. SPART.PAR is marked read-only to keep you from accidentally deleting it. If you delete SPART.PAR, Windows will not know about the permanent swap file. Also you can't delete the permanent swap file with the Swapfile utility because Swapfile also reads SPART.PAR. The Swapfile utility makes DOS calls that cannot be made from protected mode Windows. Therefore, SWAPFILE.EXE can be run only from real mode Windows 3.00 to create or delete a permanent swap file and cannot run with other applications. If the Swapfile utility program says that the maximum swap file size it can create is smaller than your free disk space, your hard disk is fragmented. If you want to create a larger permanent swap file, you must optimize your hard disk (optimizing is also known as unfragmenting, or compacting). This must be done with a third-party utility program such as Bridgeway Publishing FastTrax, Norton Utilities, Mace Utilities, Golden Bow VOpt, or Central Point PCTools. If you have already created a permanent swap file, make sure to delete it using the Swapfile utility program before optimizing your hard disk. It is not necessary to delete the permanent swap file every time you optimize your hard disk -- only when you want to increase the size of the permanent swap file by optimizing, then re-creating it. The Swapfile utility program supports only disks that use 512-byte sectors. If 512-byte sectors are not being used, this indicates a nonstandard configuration such as a third-party disk partitioning driver. Swapfile (and Windows 3.00 itself) supports drives with 512-byte sectors that have been partitioned with the DOS FDISK utility. Never run Swapfile on a drive that uses a partitioning driver in the CONFIG.SYS, with the exception of COMPAQ's ENHDISK.SYS. If you receive a message that your swap file is corrupted, run the Swapfile utility, delete the current swap file, and create a new one. PAGING TO NETWORK DRIVES Paging to a network drive, while certainly possible, is extremely slow and is not recommended. Only temporary swap files can be used on network drives. If you want to page to a net drive, the directory must not have a DOS Read-Only attribute. You must have Create and Write access to the directory. Note that because they are not MSNet-Redirector compatible, the root of a Novell network drive is the root of the server. Do not set the PagingDrive= parameter to a Novell network drive. If you do so and multiple users run Windows 3.00 enhanced mode, their computers will hang because they will overwrite each other's swap files, all with the same name and all created in the root directory of the server. ====================================================================== WIN.COM AUTOMATIC START-UP PARAMETERS ====================================================================== WIN.COM starts up automatically in the appropriate Windows 3.00 operating mode for your machine and the amount of memory installed. These modes are real mode (similar to Windows/286 2.x), 286 standard mode (also known as 286 protected mode), and 386 enhanced mode (also known as 386 protected mode). However, Windows may be forced into one of the three modes through the following command-line switches: Command Line Mode ------------ ---- WIN /R Real WIN /S or WIN /2 Standard WIN /3 Enhanced REAL MODE REQUIREMENTS ====================== The requirements for WIN.COM to automatically start up in real mode are the following: * 8088 processor or above * 384K of free conventional memory (393,216 bytes reported by CHKDSK) STANDARD MODE REQUIREMENTS ========================== The requirements for WIN.COM to automatically start up in standard mode are the following: * 80286 processor or above * 192K of free extended memory * XMS driver loaded (HIMEM.SYS) ACTUAL STANDARD MODE REQUIREMENTS Standard mode conventional/extended memory requirements are mutually dependent and are not fixed. A typical installation requires a minimum of 128K free at the DOS prompt to run standard mode, assuming sufficient extended memory is free. Standard mode requires between 384K and 512K combined conventional and extended memory to run (approximately). For example, if only the minimum 192K of extended memory is free, approximately 322K of conventional memory is required to run standard mode. However, If available extended memory is increased to approximately 208K or greater, only 128K of conventional memory is required. This example is intended to illustrate that memory requirements are interrelated and variable. ENHANCED MODE REQUIREMENTS ========================== The requirements for WIN.COM to automatically start up in enhanced mode are the following: * 80386 processor or above * 1024K of free extended memory * XMS driver loaded (HIMEM.SYS) ACTUAL ENHANCED MODE REQUIREMENTS See the above notes for standard mode regarding the interrelationship of conventional and extended memory requirements. A typical installation requires a minimum of 182K free at the DOS prompt to run enhanced mode, assuming sufficient extended memory is free. Enhanced mode requires between 580K and 624K combined conventional and extended memory to run (approximately). Note that enhanced mode can start up in low memory situations only because it provides virtual memory support. However, it may be extremely slow due to the large amount of disk swapping it must perform. All numbers are approximate and may vary widely depending on the configuration (for example, Windows device drivers chosen, DOS version, display adapter, etc.). 128K of extended memory is recovered from shadow RAM usage on COMPAQ 386 machines. Memory requirements take into account memory that can be recovered from SMARTDrive (down to the minimum cache size specified). ====================================================================== THE FREE SYSTEM RESOURCES PERCENTAGE ====================================================================== The Program Manager and File Manager Help About boxes in Windows 3.00 standard and enhanced modes give percentage figures for Free System Resources and Free Memory. To understand what the Free System Resources percentage means, you must understand some of the anatomy of Windows' internal structure. The part of Windows that runs Windows applications is made up of three main segments called KERNEL, GDI (graphics device interface), and USER. KERNEL loads and executes Windows applications and handles their memory management. GDI manages graphics and printing. USER controls user input and output, including the keyboard, mouse, sound driver, timer, and communications ports. In Windows 2.x these modules are linked to the files WIN200.BIN and WIN200.OVL by the Setup program, so you can't see them in the Windows directory. In Windows 3.00, they're separate and are located in the SYSTEM subdirectory. Both USER and GDI have storage areas that are limited to 64K in size. A storage area limited to 64K is known as a local heap. The Free System Resources percentage reflects the remaining free percentage of combined USER and GDI local heap space. Although Windows 3.00 allows you to run a much larger number of simultaneous Windows applications than any previous Windows version, it is not without limitations. If you receive an Out of Memory error and the Help About box shows a large amount of Free Memory, look at the Free System Resources percentage. Chances are you are low on system resources. Every window, subwindow, and icon that is created requires GDI local heap space. It is theoretically possible to exhaust the system resources with only one application, such as Program Manager, if enough objects are created by the application. Another important aspect of Windows application memory management that is not included in the Free System Resources percentage is the number of selectors. A selector is a memory pointer that is consumed with each memory allocation made by a Windows application. Windows 3.00 has a fixed number of selectors. If a Windows application allocates a very large number of small data objects, it is possible to run out of selectors. This will produce an Out of Memory error message. Writing a Windows application to handle its own data objects more efficiently can help in this situation. If you experience a chronic problem with a particular application while few or no other applications are loaded, contact the application vendor. It is important that the vendor becomes aware of the problem so the problem can be corrected if possible. However, please note that this is a Windows 3.00 limitation, not an application problem. Writing an application to handle data objects efficiently can reduce, but not eliminate, the problem. ====================================================================== ENHANCED MODE PERFORMANCE TIPS ====================================================================== Getting the most from your machine The following suggestions should assist in maximizing the performance of your Windows 3.00 enhanced mode installation. Many of these suggestions apply to standard and real modes as well. 1. Use SMARTDrive. The Microsoft SMARTDrive disk caching driver can produce the largest single Windows 3.00 performance improvement. Use SMARTDrive whenever possible. Allocate the largest amount of memory to SMARTDrive without impairing your ability to run your desired applications. For basic information on SMARTDrive installation and operation, refer to the Microsoft Windows User's Guide version 3.0 manual. 2. Keep your hard disk optimized. A fragmented hard disk greatly impacts Windows' performance, especially when a temporary swap file and/or SMARTDrive is installed. Use a hard disk optimizer program on a weekly basis to keep your disk contiguous. 3. Create a permanent swap file. Using a permanent swap file improves performance over using a temporary one. See the "Enhanced Mode and Virtual Memory" section of this application note for more information on permanent swap file allocation. 4. Turn off graphics port trapping. The speed of running DOS applications under enhanced mode can be noticeably improved by not selecting any of the Monitor Ports options in the Advanced section of the PIF Editor. The High Graphics option is on by default to provide the widest range of DOS application compatibility but is not required for most applications. 5. Turn off the FileSysChange= option. Windows 3.00 enhanced mode can monitor disk access by DOS applications and send directory update messages to the File Manager. This allows the File Manager to be automatically updated by changes made to files or directories by DOS applications. However, it is not a necessity and leaving this option off (the default) speeds file access by DOS applications. To disable this feature, set FileSysChange=no in the [386ENH] section of the SYSTEM.INI file. 6. Turn off the ReservePageFrame= option. Turn this option off if you do not require expanded memory support for DOS applications. Turning this option off ensures that you're getting the most possible memory in virtual machines. To disable this feature, set ReservePageFrame=no in the [386ENH] section of the SYSTEM.INI file. 7. Use the right number of DOS buffers. If you are using SMARTDrive, set the number of DOS disk access buffers in your CONFIG.SYS file to 15 (that is, BUFFERS=15). Using a greater number of buffers with SMARTDrive will actually decrease efficiency. If you are not using SMARTDrive, use BUFFERS=30. 8. Use the lowest common display driver. Using a display driver with a higher resolution or greater number of colors results in slower display performance. If you do not require the extra features of the display driver, use a driver with less capability. Usually this suggestion applies to display systems that are VGA compatible but offer an extended mode driver, such as the Video Seven or 8514. Using the standard VGA driver instead offers faster display performance but less resolution and/or color support. 9. Use the proper hard disk interleave. Frequently, a hard disk is formatted with the wrong interleave at the dealer or factory. You can use a program such as Gibson Research's SpinRite to verify that you are using the proper interleave. Some utilities can correct your interleave without reformatting the hard disk. ====================================================================== EXPANDED MEMORY FOR DOS APPLICATIONS ====================================================================== UNDER REAL MODE WINDOWS 3.00 ============================ Real mode Windows 3.00 and DOS applications can both use the same external Expanded Memory Manager (EMM). Expanded memory can be provided either by a physical expanded memory board, or by a 386 Expanded Memory Manager. Common expanded memory boards include the Intel Above Board and AST RAMpage. Common 386 Expanded Memory Managers include Microsoft EMM386.SYS (included with the Windows product), COMPAQ CEMM.EXE (included with COMPAQ 386 machines), Qualitas 386 to the Max (386MAX.SYS), and Quarterdeck QEMM.SYS. If a physical expanded memory board is used, you will get the best performance from real mode Windows by backfilling to provide large page frame LIM 4.0 support. Some boards do not have the hardware register support to provide large page frame LIM 4.0 -- only small page frame (see the "Expanded Memory" section of this application note). All 386 Expanded Memory Managers provide large page frame LIM 4.0 support. Remember that DOS applications require LIM 3.2 (a 64K contiguous page frame) to use expanded memory, but real mode Windows requires LIM 4.0 (does not require a 64K contiguous page frame). If you see expanded memory in Windows but not in your DOS applications, you probably do not have a 64K contiguous page frame (LIM 3.2), and you may need to rearrange adapter locations. Refer to the "Expanded Memory" section of this application note for more information. UNDER STANDARD MODE WINDOWS 3.00 ================================ As noted in the standard mode section of "Windows 3.00 Modes and Memory Usage" of this application note, Windows 3.00 standard mode does not use expanded memory. DOS applications running under standard mode can use expanded memory only with a physical expanded memory card such as an Intel Above Board or AST RAMPage. 386 Expanded Memory Managers cannot be used to provide expanded memory support for DOS applications running from standard mode. Still, 386-compatible EMMs can be loaded to provide DOS application expanded memory support outside of standard mode. UNDER ENHANCED MODE WINDOWS 3.00 ================================ Expanded memory emulation is provided internally for DOS applications running under enhanced mode. The only requirement is the presence of a 64K contiguous page frame. See the "Enhanced Mode and the 384K Reserved I/O Address Space" section of this application note for more information on page frame placement. Expanded memory for DOS applications can be allocated and/or limited via PIF parameters. EXTERNAL 386 EXPANDED MEMORY MANAGERS ===================================== Some 386 Expanded Memory Managers have a special feature that allows standard or enhanced mode Windows to turn them off when Windows is run. Memory managers with this capability are EMM386.SYS and CEMM.EXE. Windows can turn off EMM386.SYS even if expanded memory is in use at the time. CEMM.EXE requires that no expanded memory be in use when standard or enhanced mode Windows is run. Other memory managers such as 386MAX and QEMM cannot be loaded with standard or enhanced mode Windows. Some 386 Expanded Memory Managers provide the capability to load DOS device drivers into free areas of the 384K reserved I/O address space. This process works correctly under real mode Windows, and if you must run real mode, this is recommended for best performance. EMM386.SYS and CEMM.EXE do not provide this capability, but 386MAX.SYS and QEMM.SYS do. If you plan to switch back and forth between real mode and standard or enhanced mode Windows 3.00, we recommend using EMM386.SYS. Neither standard nor enhanced mode will run with 386MAX or QEMM. Using one of these memory managers requires you to reboot with a different CONFIG.SYS and AUTOEXEC.BAT to switch between Windows 3.00 operating modes. Using EMM386.SYS allows you to run whichever mode you want. ====================================================================== DPMI AND VCPI ====================================================================== SPECIFICATIONS FOR DIFFERENT PURPOSES ===================================== The DOS Protected Mode Interface (DPMI) was developed by a group of industry leaders including Borland, Eclipse, IBM, IGC, Intel, Locus, Lotus, Microsoft, Phar Lap, Quarterdeck, and Rational Systems. Several members of the DPMI committee were also involved in the creation of the Virtual Control Program Interface (VCPI). DPMI is primarily a creation of Microsoft, and VCPI was formulated primarily by Phar Lap Software. DOS EXTENDED APPLICATIONS ========================= DOS extended applications execute code in the protected mode of the 80286 or 80386 processor. Unlike OS/2 applications, DOS extended applications are launched from standard MS-DOS or PC-DOS. Creating a DOS extended application requires a method to switch the processor to protected mode and to allocate extended memory. Until DPMI, there has been no standard method for DOS extended applications to perform these tasks plus multitask memory with other applications on 80286 processors. Hundreds of existing applications have been created using various types of DOS extenders. OS/2 extender applications that do not already support DPMI will require minor modifications to do so. COMPARING VCPI TO DPMI ====================== VCPI and DPMI solve two different problems. VCPI provides an interface between applications using DOS extenders on an 80386 machine, and 386 Expanded Memory Managers. For example, the 386 Expanded Memory Managers QEMM, 386MAX, and CEMM support the VCPI specification. VCPI allows applications using DOS extenders to run simultaneously with 386 Expanded Memory Managers on a 386 machine. However, multitasking operating environments such as Windows 3.00 enhanced mode, OS/2, UNIX 386, and VM386 have memory and protection models that are not compatible with the VCPI interface. DPMI was created so these environments can run extended DOS applications. Additionally, DPMI provides support for 80286-based machines, which VCPI does not. DPMI has the capability of running DOS extended applications on a variety of processors and operating environments. ====================================================================== GLOSSARY ====================================================================== 386 Expanded Memory A device driver loaded that provides expanded Manager (EMM) memory on an 80386-based computer without a physical expanded memory board. 386 Expanded Memory Managers operate via the 386 processor's hardware capabilities. 386MAX.SYS A 386 Expanded Memory Manager from Qualitas Corp. CEMM.EXE A 386 Expanded Memory Manager from COMPAQ. CEMM is provided with all COMPAQ 386-based computers. It carries an extension of .EXE rather than .SYS even though it is installed in the CONFIG.SYS file like other 386 Expanded Memory Managers. Conventional Memory The memory in your machine from 0K to 640K. DPMI The DOS Protected Mode Interface (DOS extender industry standard). Applications that use the DPMI specification can run in protected mode and break the 640K barrier under standard or enhanced mode Windows 3.00. The DPMI specification is available from Intel Corporation. EMM386.SYS The Microsoft 386 Expanded Memory Manager. See the Windows 3.00 user's guide for more information. EMM Expanded Memory Manager. EMS Expanded Memory Standard. There are two Expanded Memory Standards, which are designated LIM 3.2 and LIM 4.0. Expanded Memory Manager A device driver that provides an interface to (EMM) expanded memory. An Expanded Memory Manager, or EMM, is either specific to a particular physical expanded memory board, or uses the 386 processor. Extended Memory Memory in your machine above 1 MB. Extended memory always starts at 1024K. Large Page Frame A slang term denoting the presence of bankable expanded memory pages in conventional memory. It is usually used to refer to an amount of bankable pages equal to or greater than 384K (that is, bankable pages ranging from 256K to 640K). Note that the term "large page frame" is a misnomer. The page frame is actually never any larger than four 16K pages and is always located in the 384K reserved I/O address space. Additional bankable pages in conventional memory do not make the page frame larger; they simply provide additional bankable pages. LIM 3.2 The Lotus/Intel/Microsoft expanded memory standard (EMS) version 3.2. It provides for a maximum of four 16K bankable pages that must be contiguous. LIM 4.0 The Lotus/Intel/Microsoft expanded memory standard (EMS) version 4.0. It provides for a maximum of 64 16K bankable pages, which do not have to be contiguous. Page Frame An area within the 384K reserved I/O address space that is designated the expanded memory page frame. The page frame itself can be a maximum of four 16K pages. QEMM386 A 386 Expanded Memory Manager by Quarterdeck Corp. Small Page Frame A slang term denoting the presence of expanded memory that does not place bankable pages within conventional memory. VCPI An 80386 memory management standard created by Phar Lap Software in conjunction with other software developers. VM Virtual machine. VM is a protected memory space created through the hardware capability of the 386 processor. Virtual Memory A term stating the combination of conventional, extended, and hard drive factor memory. Virtual Hard Drive The available space on a hard drive partition Memory Factor that Windows can address as physical memory. VMM Virtual Memory Manager. XMS The Microsoft eXtended Memory Specification. The XMS provides a standard way for real mode applications to access extended memory. DOS applications running under Windows 3.00 can use the XMS to access extended memory. The XMS document and sample source code is available from the Microsoft Information Center at (800) 426-9400 [international callers should call (206) 882-8661].