When your program calls dynamic allocation using SYC 99 or the DYNALLOC macro, you can use the XTIOT option, which is bit S99TIOEX. It causes creation of an XTIOT entry instead of an entry in the TIOT. The XTIOT resides above the 16 MB line. This option requires your program to be APF authorized, in supervisor state, or in a system key (0–7).

With dynamic allocation, you can use the NOCAPTURE option, which is bit S99ACUCB. If the actual UCB address is above the 16 MB line and you do not code LOC=ANY option on the DCBE macro, then, OPEN and EOV will capture it and EOV and CLOSE will uncapture it. (Capturing means to create a 24–bit address for a UCB that has an actual address above the 16 MB line. This NOCAPTURE option also causes creation of an XTIOT instead of a TIOT entry, but it does not require your program to have authorization). If you code the LOC=ANY option on the DCBE, then OPEN will not capture the UCB and its address will be in a four-byte field in the DEB.

With dynamic allocation, you can use the S99DSABA bit, which allows the DSAB control block to reside above the 16 MB line. If you turn S99DSABA on, then you must also turn on S99TIOEX and your program must be authorized.

The purpose of these three dynamic allocation options (XTIOT, NOCAPTURE, and LOC=ANY) is to reduce use of storage below 16MB. BSAM, BPAM, and QSAM also support these three options.

To learn whether the allocation has any of these three options, issue the DEVTYPE macro with the INFO=AMCAP option. On a system before z/OS® V1R11, bits S99DSABA and S99TIOEX will be off. On a release V1R12 or later system, these options should only be used when NON_VSAM_XTIOT=YES is specified in the DEVSUPxx parmlib member. This is represented by the DFAXTBAM bit in the DFA as mapped by IHADFA.