The MIDAW facility is a method of gathering and scattering data from and into discontinuous  storage locations during an I/O operation. The MIDAW format is shown in Figure 7-3. It is  16 bytes long and aligned on a quadword. An example of MIDAW usage is shown in Figure 7-4. The use of MIDAWs is indicated by the MIDAW bit in the CCW. If this bit is set, the skip flag  cannot be set in the CCW. The skip flag in the MIDAW can be used instead. The data count in  the CCW must equal the sum of the data counts in the MIDAWs. The CCW operation ends  when the CCW count goes to zero or the last MIDAW (with the last flag) ends.  The combination of the address and count in a MIDAW cannot cross a page boundary.  Therefore, the largest possible count is 4 K. The maximum data count of all the MIDAWs in a  list cannot exceed 64 K, which is the maximum count of the associated CCW. The scatter-read or scatter-write effect of the MIDAWs makes it possible to efficiently send  small control blocks that are embedded in a disk record to separate buffers from those that  are used for larger data areas within the record. MIDAW operations are on a single I/O block,  in the manner of data chaining. Do not confuse this operation with CCW command chaining. 298  IBM z15 (8561) Technical Guide Figure 7-4 MIDAW usage Figure 7-3 MIDAW format