System/370 Extended Architecture: Design Considerations

This paper reviews the overall objectives and the design considerations that led to the System/370 Extended Architecture (370-XA). It presents an overview of the differences between the System/370 and 370-XA architectures and summarizes all architectural extensions, deletions, and changes. Then it describes in more detail the extensions for interpretive execution, 31-bit addressing, protection, tracing, inter-CPU communications, and extended-precision floating-point division.