The OpenVMS Alpha and Integrity server 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 Integrity server 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 $QIO system service, and most of the device drivers supplied with OpenVMS Alpha and Integrity server systems. A device driver declares support for 64-bit addresses individually by I/O function code. Disk and tape device drivers support 64-bit addresses for data transfers to and from disk and tape devices on the virtual, logical, and physical read and write functions. For example, the OpenVMS SCSI disk class driver, SYS$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.