S/390

S/390
Name	S/390
Developer	International Business Machines Corporation
Released	1990s
Predecessor	System/370
Successor	z/Architecture
Type	Mainframe

S/390 S/390 is a mainframe server architecture introduced by International Business Machines Corporation as an evolution of System/370 to support enterprise-scale transaction processing, batch workloads, and virtualization. It consolidated decades of designs from IBM System/360, System/370, and related IBM product lines while interoperating with software developed for VM/CMS, MVS, and later OS/390. S/390 played a central role in large installations run by entities such as Deutsche Bank, HSBC, JPMorgan Chase, Bank of America, Federal Reserve System, U.S. Internal Revenue Service, and national data centers in France, Japan, and United Kingdom.

History

The S/390 lineage arises from architectural transitions that began with IBM System/360 and continued through System/370 and System/370-XA. During the late 1980s and early 1990s, IBM consolidated microcode advances from projects including System/390 Parallel Sysplex work and research from the IBM Research labs. Major milestones include announcements and product refreshes that aligned with enterprise demands from organizations like AT&T, General Electric, Siemens, Royal Bank of Scotland, and public administrations such as the United Kingdom Cabinet Office. The introduction of S/390 coincided with industry trends toward open standards driven by Unix variants such as AIX and influenced by interoperability initiatives like the Open Systems Interconnection model. Corporate alliances and procurement by firms like Accenture, PricewaterhouseCoopers, and Capgemini helped proliferate S/390 deployments in service bureaus and outsourcing arrangements.

Architecture and Design

S/390 retains a CISC heritage traceable to IBM System/360 while incorporating microarchitectural techniques explored in projects at IBM Research and in competition with vendors such as Fujitsu, Hitachi, and Unisys. Key design elements include a 31-bit general-purpose addressing model extended toward 64-bit concepts that later culminated in z/Architecture. S/390 systems implemented features for high-availability and data integrity such as hardware-assisted recovery mechanisms used in conjunction with Geographically Dispersed Parallel Sysplex configurations and clustering techniques drawn from Parallel Sysplex designs. Redundancy, channel I/O concepts originating from IBM System/360 Model 67, and integrated cryptographic hardware—later standardized by initiatives like Common Criteria evaluations used by defense and banking sectors—were prominent. The architecture supported virtualization primitives that enabled hypervisor-like environments foundational to VM/370 and subsequent virtual machine monitors.

Instruction Set and Compatibility

The S/390 instruction set preserved backward compatibility with legacy code written for System/370, System/360, and software built on MVS, VM/CMS, and OS/VS2. This compatibility allowed institutions operating legacy applications from vendors such as SAP, Oracle Corporation, SAS Institute, Micro Focus, and bespoke in-house systems at entities like General Motors and Lockheed Martin to migrate hardware without rewriting critical business logic. S/390 introduced new instruction encodings and privileged instructions to support virtualization, symmetric multiprocessing, and I/O channel control while maintaining compatibility layers expected by compilers from IBM Rational and language ecosystems including COBOL, PL/I, FORTRAN, C, and Assembler (computing) toolchains. Emulation and binary translation technologies from third parties such as Fujitsu and Amdahl vendors were sometimes used to bridge differences between S/390 and competing hardware.

Implementation and Models

IBM produced multiple S/390 models targeting different performance and scale points, comparable to model families produced historically by Amdahl Corporation and contemporaries like Hitachi mainframe product lines. Enterprise installations ranged from rack-mounted configurations housed in data centers operated by E*TRADE-class financial firms to large frame installations used by national postal services and telecommunications providers such as Deutsche Telekom and NTT. S/390 implementations incorporated microcode updates, dedicated I/O processors modeled on IBM channel I/O concepts, and optional cryptographic coprocessors conforming to standards used by institutions like Visa and Mastercard. Systems were often sold with service agreements provided by IBM Global Services and integration partners including DXC Technology and Tata Consultancy Services.

Operating Systems and Software Support

S/390 ran a range of IBM and third-party operating systems, most notably MVS family derivatives culminating in OS/390 and later z/OS after the evolution to z/Architecture. Virtualization stacks based on VM/CMS and tools for middleware such as CICS, IMS (information management system), DB2, and WebSphere provided transaction and database services used by industries ranging from banking to airlines, including clients like American Airlines and Delta Air Lines. Third-party software vendors—CA Technologies, BMC Software, Micro Focus, and Compuware—supported management, batch scheduling, and development tools. Integration with networking stacks and standards like TCP/IP enabled connectivity to distributed systems and clients running Windows NT, Solaris, and Linux variants deployed by enterprises.

Performance and Impact on Mainframe Computing

S/390 reinforced mainframes' role for mission-critical throughput, high I/O concurrency, and transaction integrity in sectors such as banking, insurance, and government. Benchmarks and real-world deployments demonstrated strengths in transaction-per-second metrics for applications hosted under CICS and throughput for large-scale batch processing used by tax agencies and clearinghouses. The architecture influenced subsequent designs including z/Architecture and competitive offerings from Fujitsu and Hitachi, and informed virtualization, security, and reliability expectations across the IT industry. Organizations such as The Open Group and standards bodies monitored mainframe evolution, while consulting firms documented migrations and total cost-of-ownership studies supporting decisions by CIOs at IBM customer organizations.

Category:IBM mainframe computers