Specifications

Data Structures
1.19 Unit Control Block (UCB)
Table 1–22 (Cont.) Contents of Unit Control Block
Field Name Contents
DEV$V_RED Redirected terminal
DEV$V_NNM Device name has a prefix of the format ‘‘node$’’
DEV$V_WBC Device supports write-back caching
DEV$V_WTC Device supports write-through caching
DEV$V_HOC Device supports host caching
DEV$V_LOC Device is accessible via local (non-emulated) controller
DEV$V_DFS Device is DFS-served
DEV$V_DAP Device is DAP accessed
DEV$V_NLT Device is not-last-track; that is, it has no bad block
information on its last track
DEV$V_SEX Device supports serious exception handling (tape)
DEV$V_SHD Device is a member of a host-based shadow set
DEV$V_VRT Device is a shadow set virtual unit
DEV$V_LDR Loader is present (tape)
DEV$V_NOLB Device ignores server load balancing requests
DEV$V_NOCLU Device will never be available clusterwide
DEV$V_VMEM Device is a virtual member of a constituent set
DEV$V_SCSI Device is a SCSI device
DEV$V_WLG Device has write logging capability
DEV$V_NOFE Device does not support forced error
DEV$V_AIP Allocation is in progress (MME)
DEV$V_CRAMIO Device supports CRAM mailbox I/O
UCB$L_AFFINITY* Bit mask of the CPU-IDs of processors in a multiprocessing system that have
physical connectivity to the device. Such processors can thereby access the
device’s registers and initiate I/O operations on the device.
UCB$L_XTRA SMP alternate STARTIO wait.
UCB$B_DEVCLASS Device class. The DPT of every driver should specify a symbolic constant
(defined by the $DCDEF macro) for this field. The driver-loading procedure
writes this field when it creates the UCB.
Drivers with set mode and device characteristics functions can rewrite
the value in this field with data supplied in the characteristics buffer, the
address of which is passed in the I/O request.
The following device classes are defined:
DC$_DISK Disk
DC$_TAPE Tape
DC$_SCOM Synchronous communications
DC$_CARD Card reader
DC$_TERM Terminal
DC$_LP Line printer
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