Device Driver Support for
OpenVMS Alpha 64-Bit Addressing
The OpenVMS Alpha operating system provides support for 64-bit
virtual memory addressing, which makes the 64-bit virtual address
space defined by the Alpha architecture available to the OpenVMS
Alpha operating system and to application programs. In the 64-bit
virtual address space, both process-private and system virtual address
space extend beyond 2 GB. By using 64-bit addressing features, programmers
can create images that map and access data beyond the limits of
32-bit virtual addresses.
Input and output operations can be performed directly to and
from the 64-bit addressable space by means of RMS services, the
$QIO system service, and most of the device drivers supplied with
OpenVMS Alpha systems. A device driver declares support for 64-bit
addresses individually by I/O function code. Disk and tape device
drivers support 64-bit addresses for data transfers to and from
disk and tape devices on the virtual, logical, and physical read
and write functions. For example, the OpenVMS SCSI disk class driver, SYS$DKDRIVER,
supports 64-bit addresses on the IO$_READVBLK and IO$_WRITEVBLK
functions, but not on the IO$_AUDIO function. The device drivers,
function codes, and $QIO arguments that support 64-bit addressing
are indicated in the appropriate chapters of this manual.
For more information about the OpenVMS Alpha device drivers
that support 64-bit addressing, see the OpenVMS Programming Concepts Manual.
To find out how to modify a customer-written device driver to support
64-bit addressing, see the OpenVMS Alpha Guide to Upgrading Privileged-Code Applications Manual.
HP OpenVMS I/O User's Reference Manual
Preface
