## Physical Device Driver Reference

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### Block Device Drivers

These drivers support I/O for block or record oriented devices. These devices are usually characterized by one or more of the following:

Random access
Reading data is non-destructive (persistent)
Accessing of data is difficult on byte boundaries
Utilizing Direct Memory Access (DMA)

A block device driver does not have a name; instead, a block device driver is assigned one or more drive letters. Because a block device driver can support multiple devices (or units), a drive letter is assigned by the OS/2 kernel for each device (or unit). For more information on block device drivers, refer to the Storage Device Driver Reference.