Why Banks Still Rely on IBM Mainframes: The IOE Architecture Explained

What is IOE?

IOE refers to three IT giants: IBM (I), Oracle (O), and EMC (E). Their products provide the underlying operating systems, middleware, and databases used by many enterprises.

Traditional IOE architecture – a centralized, closed‑source system where applications run on one or two servers, and the vendor supplies the operating system, middleware, and database.

Go‑IOE architecture – a distributed, open‑source system where applications run on dozens or hundreds of servers using publicly available software.

Which IBM systems do banks use?

Banks’ core banking systems vary by bank, business line, and IBM product. Major state‑owned banks (e.g., ICBC, CCB) use IBM Z series mainframes for core banking; some commercial banks use the i series; others use the p series. Many ancillary systems also run on IBM hardware.

Hardware: IBM Z series (large‑scale mainframes), i series, p series, x series (x86 servers).

Software: DB2/Informix/VSAM databases; CICS, MQ, WAS middleware; AIX, OS400, VSE, OS390 operating systems.

Most banks have hundreds of business systems, with over 70% running on IBM p series, x series, or blade servers, while the rest use various foreign vendors such as HP and Dell.

Can banks move away from IOE?

Replacing IOE faces several obstacles: the need for absolute stability and risk avoidance, massive procurement interests, a shortage of talent that understands both legacy and modern technologies, and the lack of domestic products that match IBM’s performance.

Even a new bank would need enormous investment and manpower to build a comparable mainframe capability, and the transition could take a decade.

Who can replace IOE?

IBM mainframes (Z series): no viable replacement now or in the foreseeable future.

IBM small systems (i/p series): also irreplaceable.

IBM x series (PC servers): can be substituted with domestic alternatives.

EMC/IBM storage: can be replaced for general purposes.

Oracle/IBM middleware and databases: currently not replaceable.

Conclusion

In the x‑series server and generic storage domains, domestic products can compete, but in core banking hardware and software, the legacy IOE ecosystem remains dominant.