Device Driver Support for
OpenVMS Alpha and I64 64-Bit Addressing
The OpenVMS Alpha and I64 operating systems provide support
for 64-bit virtual memory addressing, which makes the 64-bit virtual
address space defined by the architecture available to the OpenVMS
Alpha and I64 operating systems 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
$QIO system service, and most of the device drivers supplied with
OpenVMS Alpha and I64 systems. A device driver declares support
for 64-bit addresses individually by I/O function code. Disk and tape
device drivers support 64-bit addresses for data transfers to and
from disk and tape devices on the virtual, logical, and physical
read and write functions. For example, the OpenVMS SCSI disk class
driver, SYS$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 device drivers that
support 64-bit addressing, see the HP OpenVMS Programming Concepts Manual.
To find out how to modify a customer-written device driver to support
64-bit addressing, see the HP OpenVMS Guide to Upgrading Privileged-Code Applications Manual.