All IBM Mainframe and Midrange Systems

IBM produced two long-running families of enterprise computers that are grouped together here as its core business computing line. The System/360, announced in 1964, was the first computer family to cover both commercial and scientific work across a full range of machine sizes with compatible software, and IBM extended the same architecture forward through the System/370 in 1970, the System/390 in 1990, implementing the fifth-generation ESA/390 instruction set, and IBM Z, introduced in 2000 as the successor to System/390 and still sold today with full backward compatibility to decades-old software. Alongside this large-systems lineage, IBM built a separate midrange line for smaller business customers: the AS/400, announced in 1988 as the successor to the System/36 and System/38, consolidated IBM's earlier fragmented midrange computer offerings under one operating system, OS/400. Both lines share IBM as their manufacturer and a business-computing market, even though they descend from different internal architectures.