 Unwilling to bet the company on the immature monolithic IC technology of the early 1960s, IBM built the S/360 series using IBM's Solid Logic Technology (SLT) modules.SLT could package several individual transistors and individual diodes with deposited resistors and interconnections in a module one-half inch square, roughly the equivalent logic of the earlier IBM Standard Modular System card, But unlike monolithic IC manufacturing, the diodes and transistors in an SLT module were individually placed and connected at the end of each module's assembly.First generation computers were largely out of reach of schools and hobbyists who wished to build their own, largely because of the cost of the large number of vacuum tubes required (though relay-based computer projects "were" undertaken).