Some 7090 features, including index registers, character instructions and floating point, were extra-cost options.
The schedule delays caused by IBM's multiple incompatible architectures provided motivation for the unified System/360 family.
In the summer of 1965 they wrote the WATFOR compiler for their 7040, which became popular with many newly formed computer science departments.
[4][5] IBM also offered the 7040 (or 7044) as an input-output processor attached to a 7090, in a configuration known as the 7090/7040 Direct Coupled System (DCS).
[6][7] IBM used similar numbers for a model of its eServer pSeries 690 RS/6000 architecture much later.