System Startup, Configuration, and Shutdown Reference Manual (32650-90907)

Chapter 5
Modifying Input/Output (I/O) Configurations
I/O Paths
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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 **
aclass (ac) adev (ad) apath (ap) avol (av)
dclass (dc) ddev (dd) dpath (dp) dvol (dv)
lclass (lc) ldev (ld) lpath (lp) lvol (lv)
maddress(ma) mclass (mc) mdev (md) mpath (mp)
mvol (mv)
clear (cl)(c) exit (ex)(e) help (he)(h) hold (ho)