That portion of a unit control block that contains a drive ' s context while the driver is waiting for a resource 单元控制块的那一部分，该部分包括驱动程序上下文，而驱动程序正在等待资源。
2.
An area of main storage that holds the addresses of the unit control blocks and system control blocks for each symbolic unit 主存储器中存放每个符号设备的设备控制块和系统控制块的地址的一种区域。
