much smaller than SLT's metal cans. Each package contains a ceramic wafer with up to four silicon dies on top, each die implementing one transistor or two diodes; and thick-film resistors underneath. ULDs were used in the Launch Vehicle Digital Computer and Launch Vehicle Data Adapter of the Saturn V rocket. Advanced Solid Logic Technology (ASLT) increased packaging density and circuit performance by stacking two substrates in the same package. ASLT is based on the Emitter-follower-coupled-switch used with current-steering logic. ASLT voltage levels were : > +235 mV is high, < -239 mV is low. Monolithic System Technology (MST) increased packaging density and circuit performance by replacing discrete transistors and diodes with one to four monolithic integrated circuits (resistors now external from the package on the module). Each MST chip holds about five circuits and is the approximate equivalent of an SLT card. Circuits used NPN transistors. MST was first introduced in January 1968 and provided improved cost/performance for IBM's System/370 product line of the 1970s. Gallery See also Standard Modular System References External links IBM's Solid Logic Technology (SLT) 1964-1968, Vintage Computer Chips, includes video of automated manufacturing process Chip carriers Solid Logic Technology Solid Logic Printed circuit board manufacturing Computer-related introductions in 1964