TITLE
    DOS Compatibility Card: Can't Use Most DOS Backup Programs 7/95
Article ID:
Created:
Modified: 		15804
7/13/94
7/17/95
TOPIC



    We are trying to perform a backup to floppy of files from a Macintosh DOS Compatible computer.

    When we tried to configure the backup or to do it using DOS backup, a message appears saying the estimated time is 1:24. More than an hour passes and nothing occurs, no copy to disk is made. From Windows, it hangs up and we have to reset the computer. From CPBACKUP, the program hangs up when the backup is attempted, the same program works fine in a 486DX equipped PC.

    Reinstalling MS-DOS and Windows have not corrected problem.

DISCUSSION


    The problem you are experiencing is due to the program trying to write directly to the floppy drive hardware. Since we are only emulating a DOS compatible floppy drive, accessing the hardware directly fails. Backup programs in order to gain speed, typically use DMA to write to floppy drives. Since the backup programs are not using DOS BIOS calls, they fail when they don't find the actual hardware they're looking for. However, some applications, such as Norton Backup for Windows can perform backups to floppy disks.

    Norton Backup for Windows has the same problem as other backup software when using the floppy drive but Norton Backup also has a work around for this. Norton Backup for Windows has a feature to backup files to any valid DOS path. By using "A:\" as the DOS path, Norton Backup for Windows will backup to floppy disks when used with the DOS Compatibility Card.

    The DOS Compatibility Card is not a "true DOS machine", we are a "DOS compatible" machine. Because of current technology limitations, there is no way to "emulate" DMA access to an Intel x86 architectured device. Anything that tries to access hardware directly, do not work in the DOS compatible card environment. When the PC was first designed, and in subsequent revisions of the PC hardware, BIOS was designed to handle the interface between the operating system and hardware. In order to ensure software compatibility, software programmers were urged to use BIOS calls as opposed to writing directly to hardware. With our DOS compatible card, any program that makes BIOS calls should work, and any program that writes directly to hardware will probably fail.

    There are no plans to add support for floppy disk DMA access to the DOS Compatible Card. Current solutions to the problem are copying the complete drive file to a different storage device while in the Macintosh environment, or double-clicking the drive container file and copying individual files from it, also while in the Macintosh environment.


    Article Change History:
    17 Jul 1995 - Added third-party solution
    07 Nov 1994 - Added additional information on why Backup programs fail.

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Document Information
Product Area: Computers
Category: DOS Compatible
Sub Category: DOS Compatibility Cards
Keywords: kwindows

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