Document 1205
Slow Disk Transfers

Initials:
        LM
        09/18/91
	DRDOS 6.0

Keywords:
        DISK
	
Description:
        Some customers may experience very slow data transfer rates when
        their applications are doing direct disk input. The slow transfer
        rate is a result of how DR DOS handles device drivers or
        applications which use upper memory blocks while writing data to
        the disk drive

        Under DR DOS, disk access going through UMBs is transferred to
        conventional memory before it is written. It is then written one
        sector at a time. This reduces 1:1 interleave down to 17:1 which
        results in disk writes being 3 to 8 times slower than disk
        writes going directly through conventional memory. It is only a
        problem with writes to the disk, not reads.

        What would cause this slow transfer rate under DR DOS?

        1) A disk I/O driver loaded into upper memory, such as the
        Stacer disk compressor or Disk Manager. The workaround is to
        load the driver in conventional memory.

        Note: The DR DOS SuperStor driver averts this problem by leaving
        the DMA TRANSFER part of its code in conventional memory.

        2) An application that makes disk transfers through UMBs, such
        as Lotus 3, Paradox 3, Autocad 386, Autocad 11.

        Digital Research designed DR DOS to make disk writes through
        conventional memory in order to protect customers with Bus
        Master controllers (newer PS/2 models) or some older hardware.
        Without this protection, data on their drives could be severly
        corrupted.

        Digital Research is currently investigating this problem. Please
        keep in contact with technical support for more information.