Virtual Disk Device Driver

The virtual disk device driver VDSK.SYS supports access to disk via the INT 13h CBIOS service. Since the CBIOS accesses the hardware ports directly and may therefore cause problems for other processes in the system, VDSK traps the INT 13h interrupt and emulates the processing of this interrupt. Note that VDSK does not provide I/O port level access to disk controllers.

The processing of an INT 13h request typically proceeds as follows:

  • The DOS application accesses the disk using INT 13h interface; the INT 13h request is trapped by VDSK.

  • VDSK builds a device driver request packet and sends it to the physical disk device driver. The VDM is then blocked, waiting for the request to complete.

  • The physical disk device driver processes the request packet. If the disk is currently busy, the request is queued.

  • When the request is completed, the physical disk device driver notifies VDSK, which unblocks the VDM.

    Protected mode applications access disks via a programming interface which goes through the kernel's device routing mechanism and finally to the physical disk device driver. The physical device driver receives an access request packet similar to that sent by VDSK.

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