Introduction to TRANSFER Delivery System

GUARDIAN 90 and EXPAND—Distributed
Processing
The TRANSFER Delivery System
1-12 109426—Introduction to TRANSFER Delivery System
As shown in Figure 1-5, to direct an I/O request to a device, a process makes a file
system request and specifies the name of the device. If the device is a disk, the name of
the disk is further qualified by subvolume and file names. If the device is a terminal on
a multipoint line, the name of the line is qualified by a subdevice name.
EXPAND
EXPAND is an extension of GUARDIAN 90. It links geographically distributed
NonStop systems to create a network that has the same reliability, capacity to preserve
database integrity, and potential for modular expansion as a single system. EXPAND
can use any data communications link: bisynchronous lines, X.25 connections, a FOX
fiber optic link, and so on. If the network is properly designed, communication paths
are constantly available, even in the event of a line or component failure.
An application that runs on a single node does not require EXPAND.
Figure 1-5. An Input-Output Process as a Server
WRITE
on $OUT
WRITE
Complete
Requester
Input-Output
Process
Device $OUT
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