In most cases, spooling represents the most efficient
way of handling the unit record input and output of many virtual
machines. However, special cases may justify the dedication of a real
unit record device to a single virtual machine. One special case is when the virtual machine's operating system does
its own spooling, such as POWER/VS under DOS/VS or JES under OS/VS. To
eliminate double sFooling of printer output, include a DEDICATE
statement in the virtual machine's directory entry, such as:
DEDICATE OOE 002 This statement causes VM/370 to pass all virtual printer OOE output
directly to the real printer at 002. Another case where a user may want a unit record device dedicated to
his virtual machine would be if the virtual machine produced a
sufficient volume of output to keep the device busy. Users can also have the system operator dynamically dedicate a unit
record device to their virtual machine. First, send the system operator
the message:
#cp msg operator pIs attach punch at ooa
If a punch is free at OOd, the operator issues the command:
attach OOd to userid as OOd When the device is attached, VM/370 sends a confirmation message to PUN OOD ATTACHED When the device is no lenger needed, issue the command: Icp detach OOd Devices: The DEDICATE statement can be used to place a
device that --VM/370 does not support into a virtual machine's
configuraticn. To dedicate a device, the device must: • Be physically connected to the System/370 • Be supported by the virtual machine's operating system • Not violate
restriction any of the restrictions contained in
section of the Fer examFle: A directory entry can include the statement:
DEDICATE 007 012 the VM/370 where real address 012 could represent a 2671 Paper Tape Reader that is
part of the System/370 on which VM/370 is running. If the operating
system was generated with a 2671 defined at address 007, handles
the device and CCW address translation associated with reading from the
device. The operating system in the virtual machine is responsible for
error recovery and error recording procedures. QU IBM VM/370 Operating Systems in a Virtual Machine

When using the DEDICATE statement to attach a 2305 to a
virtual machine, both the real and virtual addresses must refer to the
first base device address on the unit. The first base address of the 2305 is 0 or 8 --the resulting address appears as xxO or xxB. However, when VM/370 processes the statement, it creates all eight addresses (0-7 or 8-F) for the 2305. The LINK control statement has no unique considerations for running an
operating system in a virtual machine. Use the SPECIAL control statement to add I/O devices that do not require
corresponding real devices. Some examples are: magnetic tapes,
channel-tc-channel adapters, pseudo timers, communication lines, and
devices that, while available to the System/370, are not supported by VM/370. Installaticns can use the SPECIAL control statement to specify a
virtual transmission control unit for a multiple-access operating
system. For example: If the system requires three communication lines
from a 2703, specify: SPECIAL 061 2703 IBM SPECIAL 062 2703 IBM SPECIAL 063 2703 TELE
Before a terminal can communicate with a multiple-access system, the
terminal user must issue the DIAL command:
dial userid to connect to any available line port; or issue:
dial userid 062 to connect to a particular line. Of the three lines specified in the foregoing example, one was a
teletypewriter line and two were IBM terminal lines. When the DIAL command is issued with no specific address, VM/370 connects the terminal
to any available line as defined in the SPECIAL control statement; the
line then belongs to the specified userid. If no lines are available or
if all lines are busy, VM/370 issues an error message ana does not make
the connecticn. To droF a dialed line, a user must issue the CP RESET command. Section 1. General Considerations 45