The Mainframe Six

Summary

Sidenote: The Mainframe Six Created 23 September 2022 - Updated 24 September 2022 There are six companies remaining in the mainframe industry - Hitachi, NEC, Fujitsu, Atos (formerly Bull), Unisys, and IBM. Three of those - Fujitsu, NEC, and IBM - still develop their own CPUs, though Fujitsu is likely to do so for only one more generation. If I had to speculate about where each of them is used, this is more or less what I'd end up with. IBM is global and has, as best I can tell, between 3000 and 7000 Z customers. Many of these are on very large systems; IBM scales to far higher performance levels and core counts than other vendors. Unisys is global, with higher concentrations in Latin America (especially for MCP) and East Asia (especially for OS 2200.) MCP is more common in banking and telecom, OS 2200 in airline and government. Both exited custom CPUs in the early 2010s but have fast emulators. I'd guess there's 800-1200 MCP sites and a much smaller number of OS 2200 sites - which is a little sad because OS 2200 is awesome. MCP uses an impressive high-level-language-oriented descriptor ISA, while OS 2200 uses a 36-bit ones' complement ISA with some unusual characteristics. Fujitsu is mostly global, with the notable exception of North America, and has several distinct mainframe families. The ex-Siemens BS2000 lineup and the semi-IBM-compatible GS21 family use different software but on the same 390-based custom CPUs. The former ICL family, the 29-series descriptor systems, lives on in Britain in finance and government but is slowly declining and has been primarily run emulated for over 20 years. BS2000 is concentrated in Germany, the GS21 userbase in Japan. I'd guess there's a total of 1000-1500 Fujitsu mainframe customers, with a majority being in Japan, but I'm not super confident in that. Hitachi, though they once had a thriving global business including North America, markets their systems exclusively in Japan. Until approximately 2020, they built custom CPUs, but...