ARCH
- Default
- ARCH(8)
- Recommended
- ARCH(x) where x is the lowest level of hardware your application will have to be run on, including any disaster recovery systems.
- Reasoning
- Higher ARCH settings enable the compiler to exploit
features of the corresponding and all earlier hardware models in order
to achieve the best performance.Note: Your application might abend if it runs on a processor with an architecture level lower than what you specified with the ARCH option.
- Considerations
None besides matching to hardware level
By varying only ARCH and keeping the other options at their best recommended settings, the following performance improvements were measured over a set of IBM® internal performance benchmarks:Table 1. ARCH levels with average improvement ARCH Levels Average % Improvement ARCH(9) vs. ARCH(8) 0.3% ARCH(10) vs. ARCH(9) 9.1% ARCH(11) vs. ARCH(10) 0.9% ARCH(12) vs. ARCH(11) 8.7% ARCH(13) vs. ARCH(12) 1.1% When moving from ARCH(8) directly to ARCH(13), the average performance gain on these same set of benchmarks is 23%.
Note that only the ARCH compiler option was changed for the numbers above, and the underlying hardware was an IBM z14™ machine in all cases. This means the performance gains are strictly from compiler improvements in optimizing the COBOL applications tested.
This set of benchmarks is a mix of computation intensive and I/O intensive applications. Computation intensive applications see the largest improvement: for example, one computation intensive benchmark is reduced by 86% in execution time moving from ARCH(7) to ARCH(12). Other benchmarks spend the majority of their time performing I/O operations, and relatively little time in compiler-generated code. The performance of these benchmarks is not significantly affected by the ARCH option.
For reference, the mapping between ARCH settings and hardware models is provided below:Table 2. ARCH settings and hardware models ARCH Hardware Models ARCH(8) 2097-xxx models (IBM System z10® EC)
2098-xxx models (IBM System z10 BC)ARCH(9) 2817-xxx models (IBM zEnterprise® z196 EC)
2818-xxx models (IBM zEnterprise z114 BC)ARCH(10) 2827-xxx models (IBM zEnterprise EC12)
2828-xxx models (IBM zEnterprise BC12)ARCH(11) 2964-xxx models (IBM z13®)
2965-xxx models (IBM z13s®)ARCH(12) 3906-xxx models (IBM z14)
3907-xxx (IBM z14 ZR1) modelsARCH(13) 8561-xxx models (IBM z15®)
8562-xxx (IBM z15 T02) models