1. The Evolution of S/390

2. To understand the System/390 family of products, it is useful to review a bit of history. On April 7, 1964, IBM announced System/360 family of computers. The “360” in the name referred to all points of a compass to denote the universal applicability, wide range of performance and price, and the “whole company” scope of the development effort. The System/360 Architecture owes ist existence to the genius of three scientists,Gene Amdahl,Gerry Blaauw,Fred Brook sand to the then vice president of development,B.O. Evans and his team who made it happen.

3. Although the System/360 remained unchanged for six years, just six months after its introduction, IBM executives began to plan for systems that would exploit the emerging Monolithic Circuit (MLC) technology. By the end of 1965, a draft document defining a new family of computer systems, called “NS” for New Systems, was complete. The New Systems were to be based on monolithic circuit technology and an extended System/360 architecture to be called System/370. The System/370 architecture preserved upward compatibility with application programs written for the System/360 architecture. During the development of System/370 family, IBM recognized the need to expand the amount of main storage available to application programs. This need led to virtual memory which was publicly announced in August 1972 along with the System/370 Models 158 and 168.

4. The Models 158 and 168 brought the multiprocessing configuration to the System/370 family. Additional main storage support came with the System/370 Extended Architecture (370- XA), announced in 1981 and first shipped in 1983. The next advance in the architecture came in 1988 with the introduction of the Enterprise System Architecture/370 (ESA/370). This architecture again improved virtual storage addressing by adding access registers, which allowed access to another form of virtual storage, called data spaces. Data spaces allow more data to reside in main and expanded storage, reducing I/O and improving throughput.

5. In September 1990 IBM introduced the Enterprise System Architecture/390 and the ES/9000 System/390 family of computers. The ESA/390 includes ESCON and sysplex. In 1994 IBM announced extensions to the System/390 family including additions to the ES/9000 line, which further exploit these features, and introduces new, scalable, System/390 parallel processing computers in a Parallel Sysplex environment. For IBM, two new computing directions are set with this announcement. Complementary metal oxide semiconductor (CMOS) technology is introduced as a building block for very large computers, complementing bipolar technology; and computers targeting specific application environments -- rather than the full, general- purpose environment- are introduced.

8. Architectural Integrity - Backward Compatibility Assuming no I/O conflict, IBM guarantees that binaries produced for 1965 machines will run unchanged on todays servers.