Partition support
Some IBM® displays allow you to divide the screen into areas which you can write to and read from separately, as if they were independent screens. The areas are called partitions, and features of BMS that allow you to take advantage of the special hardware are collectively called partition support.
Standard BMS is required for partitions.
- You can divide the physical screen into any arrangement of one to eight non-overlapping rectangular areas. The areas are independent from one other, in the sense that the operator can clear them separately, the state of the keyboard (locked or unlocked) is maintained separately for each, and you write to and read from them one at a time.
- Only one partition is active at any given time. This is the one containing the cursor. The operator is restricted to keying into this partition, and the cursor wraps at partition boundaries. When a key that transmits data is depressed (the ENTER key or one of the program function keys), data is transmitted only from the active partition.
- The operator can change the active partition at any time by using the “jump” key; your program can also, as explained in Determining the active partition.
- BMS also writes to only one partition on a given SEND, but you can issue multiple SENDs and you do not have to write to the active partition.
- The partition configuration is sent to the device as a data stream, so that you can change the partitions for each new task or even within a task. The BMS construct that defines the partitions is called a partition set and is described in Partition definition.
- You also can use the terminal in base state (without partitions) and you can switch from partitioned to base state with the same command that you use to change partition arrangements.
- When you specify how to partition the screen area, you also divide
up the hardware buffer space from which the screen is driven. In partitioned
devices, the capacity of the buffer is generally greater than that
of the screen, so that some partitions can be assigned extra buffer
space. The screen area allocated to a partition is called its viewport and the buffer storage is called its presentation space.
BMS uses the presentation space as its page size for the partition, so that you can send as much data as fits there, even though not all of it can be on display at once. Keys on the device allow the operator to scroll the viewport of the partition vertically to view the entire presentation space. Scrolling occurs without any intervention from the host.
- Some partitioned devices allow you to choose among character sets of different sizes. We talk about this in 3290 character size.
In spite of the independence of the partitions, the display is still a single terminal to CICS®. You cannot have more than one task at a time with the terminal as its principal facility, although you can use the screen space cooperatively among several pseudoconversational transaction sequences if they use the same partition set (see Terminal sharing).