System Startup, Configuration, and Shutdown Reference Manual (32650-90892)

118 Chapter5

Modifying Input/Output (I/O) Conﬁgurations

I/O Paths

An I/O path is the system address assigned to the device interface hardware and the

physical path used to reach an I/O device.

I/O Paths Used to Boot a System

When a system is powered on or reset, the processor-dependent code (PDC) and

I/O-dependent code (IODC) hardware routines read and initialize the I/O paths used to

boot or reboot the system. The I/O paths that are used to load the system from disk or tape

are referred to as

boot paths

. They consist of:

• the primary boot path, for booting from disk

• the alternate boot path, for booting from a tape

• the console boot path, which determines whether or not the console can boot itself

(“autoboot”) without operator intervention

Each device conﬁgured for the boot path has been assigned a unique LDEV number which

identiﬁes a physical device associated with a system. Two of the boot paths, the primary

boot path and the console boot path, require a speciﬁc LDEV. The system master volume

must be mounted on LDEV 1 for the operating system to be booted from disk and LDEV 20

must be assigned to the system console.

At system installation, these devices are assigned a default boot path, which the system

manager may redirect either through the system initialization prompts or the initial

system load (ISL) interface. For more information on system initialization and ISL, refer to

Chapter 3 , “System Startup Functions,” in this manual.

Selecting I/O Paths

An I/O path is determined by the bus converter (S) module number, the device adapter

(DA) slot number, and the device address.

Using the SYSGEN I/O Conﬁgurator

To view and modify the I/O conﬁguration from within SYSGEN, you use the I/O

conﬁgurator module. To do so, start SYSGEN and enter IO at the SYSGEN prompt.

SYSGEN displays the commands available to you. To issue a command, you can enter

either the full command name or the abbreviation shown in parentheses in Example 5-1.

Example 5-1. Starting the I/O Conﬁgurator

:SYSGEN

sysgen>IO

** I/O configurator commands **