I understand the context to be that COBOL, as a DSL for batch processing, declares its .data and .bss segments, or the equivalents on host systems, statically in the DATA DIVISION and usually doesn't dynamically allocate memory. This, coupled with CPU, memory, and I/O bandwidth reservation from a job scheduler on an exclusive hot-swappable partition on a host (z/OS aka MVS) plus USVs, redundant disks/disk ports, and networks makes "never fail" much more a consequence and primary objective of mainframe architectures where COBOL workloads are usually run.