Configuring SMARTDRV.EXE 4.0 DOUBLE_BUFFERING Properly (82856)

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To verify whether the SMARTDrive utility is necessary, enter the following command at the MS-DOS command prompt: If all of the buffering entries list "no", then double buffering is not necessary. If the double-buffering entry is contained within the CONFIG.SYS file, it may be disabled. The entry in the AUTOEXEC.BAT file should not be disabled.

If the 32-Bit Disk Access option is available, then double-buffering is probably not necessary. If the 32-Bit Disk Access option is not available, the following command line should be present in the CONFIG.SYS file

DEVICE=C:\WINDOWS\SMARTDRV.EXE /DOUBLE_BUFFER
				

where C is the drive and Windows is the directory location of the Windows 3.1 SMARTDrive utility.

If at any time the buffering entries list "yes", then the problem has been corrected. If the entry "-" appears in the DEVICE= buffering line, SMARTDrive hasn't yet determined if double buffering is necessary. This entry may be forced to change (from a "-" to a "yes" or a "no") by one of the following methods:

1. Loading drivers or TSRs (terminate-and-stay-resident) programs into UMBs (upper memory blocks).
2. Run Windows and start multiple instances of MS-DOS virtual machines. This may not trigger it to change, however, because only certain types of writes (DMA into linear != physical memory) will cause the buffering to start. If problems occur and the line still says "-", then this is most likely not the problem.

Some disk ROM BIOS versions cause Windows to crash when multitasking occurs. (Technically, this occurs when a page-fault or instance fault occurs during a read of memory-mapped I/O). Double buffering usually works around this problem because faults will not occur on the double buffer. In these cases, double buffering can be forced to start by adding a plus sign (+) to the end of the command line in the CONFIG.SYS file as follows where C is the drive and Windows is the directory location of the Windows 3.1 SMARTDrive utility.

Usually, a better approach is to disable the 32-Bit Disk Access option and use a temporary swap file.

If the machine continues to exhibit random operational problems while the 32-Bit Disk Access option is disabled, install the DOUBLE_BUFFER+ entry into the CONFIG.SYS file. Because "instance faults" on the double buffer may still occur, the complete solution is to load a 4K memory buffer before and after the double-buffer line in the CONFIG.SYS file. (Most any driver will work, as long as it does not contain Windows instance data. The idea is to ensure there is no Windows instance data in the same 4K page[s] as the double buffer.)