The virtual block device replaces the Windows 3.0 virtual hard disk device (VHD), and provides a new set of services to support multiple block device drivers. The virtual block device performs all of the functions that VHD supported in Windows 3.0. This includes entering critical sections during Interrupt 13h calls to the ROM BIOS and allocating DMA buffers when DMA hard disks are detected.
The virtual block device can work in conjunction with virtual fast disk devices, or it can work alone to improve the performance of hard disks that do not have the fast disk device support.
The virtual block device provides the following services:
BlockDev_Command_Complete
BlockDev_Find_Int13_Drive
BlockDev_Get_Device_List
BlockDev_Get_Version
BlockDev_Register_Device
BlockDev_Send_Command
BlockDev_Synchronous_Command
The virtual block device also provides the following APIs:
BlockDev_API_Hw_Detect_Start
BlockDev_API_Hw_Detect_End
BlockDev_API_Int13_Chain_Check
The virtual block device is also linked to the following structures: