IBM has often taken an ambiguous stance toward small mainframes. The 4300 machines of the early ’80s were the first physically small mainframes, but still required traditional raised floor and separate peripherals.
Introduced in 1986, the 9370 systems were intended to be “VAX-killers,” serving as departmental machines—a niche now filled by Windows and Linux Intel-based servers. What distinguished the 9370s was their (relatively) low price and power as well as their integrated disks and tape drives. These machines fit in a single, standard rack without raised floor or heavy-duty cooling.
Alas, the 9370 wasn’t the success IBM had hoped, although the next hardware generation (ES/9000) did include the 9221, which was essentially an updated 9370. The 9370s and 9221s, while not huge sellers, were popular with smaller software vendors who couldn’t justify the expense of a larger system.
IBM also tinkered with a single-user mainframe with the IBM Personal Computer XT/370, but these limited capability machines were curiosities at best. The next serious foray was the P/370, which evolved from a research project by IBM Fellow Bill Beausoleil’s group. These were true mainframe systems in a PC-size box, and were followed by the P/390 in several incarnations. The P/370 and P/390 were also mostly popular with small Independent Software Vendors (ISVs), although some shops did use them for production.
The P/390 overlapped chronologically with the Multiprise systems, which were “real” mainframes in that they used the same central processor as the 9672 G5 systems. Ranging from 3.5 to 125 MIPS, the Multiprise machines were the next step up from a P/390, and were beloved among vendors and small shops alike.
All of the systems previously mentioned implemented 24-bit System/370 or 31-bit System/390 (ESA) architecture. When 64-bit z/Architecture was announced in 2000, the Multiprise and P/390 machines were suddenly obsolete. That doesn’t mean they stopped working; IBM supported 31-bit operating systems for several more releases, but when the zSeries announcements didn’t include a Multiprise follow-on, small shops started to wonder what their next step would be.
And what about non-IBM mainframe solutions? The last of the OEMs—Amdahl and Hitachi—exited the market in 2000 after the z/Architecture announcement, claiming that the technology investment for 64-bit was prohibitive. IBM’s 1956 consent decree requiring sharing of technology with OEMs expired in 1997, and that, presumably, was a factor in Amdahl and Hitachi’s decision. IBM no longer had a legal requirement to help them compete.
For many years, the small systems gap was filled by FLEX-ES, a product from Fundamental Software that provided System/390 emulation on Intel hardware. Starting in 1993, IBM allowed small commercial installations to license the 31-bit version of FLEX-ES. By 2002, there was also a 64-bit z/Architecture version, but IBM only allowed its use by ISVs. Fundamental had a good relationship with IBM, but was a casualty of the Platform Solutions Inc. (PSI) fight: IBM’s lawyers apparently felt it couldn’t continue with FLEX-ES while fighting PSI, so 64-bit FLEX-ES licenses weren’t renewed after 2007, although 31-bit customers with perpetual licenses continue.
From 2005 to 2008, PSI offered an Itanium-based System z alternative, but PSI was unable to get IBM to agree to license its software on its platform. After more than a year of mutual name-calling and lawsuits, IBM ended the dispute by acquiring PSI, and the product was withdrawn.
IBM recently introduced its zPDT (Personal Development Tool), an emulator logically similar to FLEX-ES (albeit in no way derived from it). Originally available only to ISVs, zPDT has recently been made available to anyone who wants to develop software on z/OS using the IBM Rational products. It offers decent power on modern commodity hardware, suitable at least for development, if perhaps not for serious production (due to its lack of support for Parallel Sysplex, CPU sharing, and other Reliability, Availability and Serviceability [RAS] features of true System z hardware).