## Physical Device Driver Reference

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### 4h, 8h, 9h - Remarks

On entry, the request packet has the media descriptor set for the drive identified in the request packet header. The transfer address is a 32-bit physical address of the buffer for the data. The byte/sector count is set to the number of bytes to transfer (for character device drivers) or the number of sectors to transfer (for block device drivers). The starting sector number is set for the block device drivers. The System File Number is a unique number associated with an Open request.

The physical device driver must perform the following actions:

Perform the requested function
Set the actual number of sectors or bytes transferred
Set the status WORD in the request header

The DWORD transfer address in the request packet is a locked 32-bit physical address. The physical device driver can pass it to the DevHlp_ PhysToVirt to obtain a 16:16 address. The physical device driver does not need to unlock the address when the request is completed.

Note: The IOCtls READ and WRITE are not supported by OS/2 physical device drivers.