Mechanical Design Consideration in the ERMA System

This paper examines some of the early 1954 design concepts of ERMA (Electronic Recording Machine, Accounting), developed for the Bank of America to record commercial checking-account activity. Standardized plug-in circuit and relay modules are described which include printed wiring, an adapter for in-rack testing, and controlled air flown Emphasis is placed on reliability and easy access for maintenance and repair, by the use of integrated inter-rack raceway wiring, internal rack printed-wiring busses, and rear-access inter-connector wiring . The exclusive adoption of solderless connections for inter-package wiring, and the use of stock parts in preference to "specials" is stressed. It is discussed how standardization was accomplished in 22 different forms of 1500 electronic circuit packages, in the areas of connector pins, supply voltages, and distribution circuits. An integrated method of cooling is outlined, beginning with module-guiding metal rails fastened to a hollow shelf assembly; embracing shelf, rack, and cabinet ducts; and completed with underfloor plenums. The associated closed-loop cooling and filtering system is shown, which used a bypassed chilled-water arrangement and an electrostatic air filter. Special equipment, such as magnetic drums, cross-bar switch assemblies, and tape-transport mechanisms are treated. It is pointed out, when any complex device such as ERMA is being pioneered, that the design of the individual components must often be based on incomplete information -- leading to a change in specifications as functional relationships become more apparent. A specific warning is sounded that the number of inter-rack leads are usually underestimated, with an attendant poor access to terminals. Sixteen photographs contribute to a detailed presentation of the completed design.