of capabilities and prices with a unified architecture, to replace its earlier computers. 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. Schools and hobbyists 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). The fourth generation (VLSI) was also largely out of reach, too, due to most of the design work being inside the integrated circuit package (though this barrier, too, was later removed). So, second and third generation computer design (transistors and LSI) were perhaps the best suited to being undertaken by schools and hobbyists. See also History of computing hardware List of transistorized computers References