Technical data

controller function for your system is implemented on the CPU module, but
a second network controller, the DESQA Ethernet adapter module, can be
added to your system.
1.2.2.5 Real-Time Controllers
Real-time controllers interface with devices that monitor or control
particular processes; for example, laboratory equipment or manufacturing
equipment connected to the system. Typically, real-time controllers are
parallel devices, not serial devices.
1.2.2.6 Printer Interfaces
Some printers require specific interfaces to communicate with the system.
For example, the LG01, LG02, and LP29 and LP37 printers require the
LPV11–SA interface module.
1.2.2.7 Other Available Options
Your system arrives configured with the options you ordered. As your needs
change, you can add more options. Your Digital sales representative can
advise you on available options. VAX 4000 Model 200 Technical Information
describes the options currently available for VAX 4000 systems. Digital
provides installation for additional options that you order.
1.3 Dual-Host Capability (VMS Systems Only)
A dual-host system consists of two systems in a VAXcluster sharing their
ISEs through a Digital Storage Systems Interconnect (DSSI) bus. Each
system can have direct access to any of the ISEs in either system; this can
include a shared common system disk.
The primary application for such a configuration is a VAXcluster system.
The simplest dual-host configuration, for example, is to configure one
system disk to be used as the system disk by both systems. The system
disk physically resides in one enclosure; however, both systems have equal
access to the system disk and to any other DSSI mass storage device in
either enclosure over a common DSSI bus.
A DSSI device, such as the RF72, has a built-in dual-host capability
that allows it to connect to two DSSI host adapters. The DSSI storage
adapter, embedded in the system’s CPU, allows you to extend a DSSI bus
by physically connecting it to another system.
Using an external DSSI cable, any two DSSI-based systems can be
connected to form a dual-host configuration. Figure 1–13 shows a dual-
host configuration with two VAX 4000 systems.
System Overview 1–25