2. When using the SPOOL, DEDICATE, and SPECIAL directory control
statements to define virtual devices, the user must specify virtual
addresses that do not conflict or contend with the virtual centrol
unit interface. This conflict or contention occurs tecause devices
can require special I/O interface protocol from control units such
as shared and nonshared sunchannel operations. Putting devices that
require different read control units on the same virtual centrol
unit can result in a hung or busy condition. 10 avoid this problem,
the user must define (and separate) devices within their own centrol
unit range. For example, if the directory entries specify: SPOOL 102 3211 SPECIAL 103 3270 the control unit 0 on channel 1 controls both a nonshared device
(the 3211 printer) and a shared device (the 3270 display unit).
Processing of channel programs involving these two devices can
result in a hung or busy condition. Section 64 Changes to V!j370 Restrictions 6-3
6-4 IBM VM/370 Release 6 Guide
Previous Page Next Page