Which of the following electronic technologies is the key technology for…

Concept

Computer generations are classified by the electronic switching device used to build the machine’s logic circuitry. The criterion is one of hardware fabrication: whichever component realises the logic gates of the processor and memory gives that generation its name. Software, applications and instruction styles do not define a generation.

Generation → switching device

Application to this question

The question asks for the key technology of the third generation, so the third row of the table is the entry to identify: the integrated circuit. Invented independently by Jack Kilby (1958) and Robert Noyce (1959), an IC places many transistors, resistors and their metal interconnections on a single silicon chip instead of soldering each component separately. Machines built from monolithic chips of this kind include the Apollo Guidance Computer (1966), whose logic was almost entirely IC NOR gates, the PDP-8/I (1968), the first PDP-8 wired from TTL chips, and the IBM System/370 (1970). One nuance is worth knowing: the IBM System/360 of 1964 is conventionally taken as the opening of this generation even though its Solid Logic Technology units were hybrid modules rather than fully monolithic chips. Either way the defining direction of travel is integration onto a chip, so the correct choice is the integrated-circuit (IC) based technology.

Because the components are made together on one chip, the machine becomes physically smaller, draws far less power, generates less heat and fails far less often. It is this packaging step, rather than any change in the underlying transistor physics, that is treated as the start of a new generation.

Cross-check against the other technologies

• Vacuum tube — the glass valve of the first generation. Bulky, power-hungry and prone to burning out, it was already obsolete well before the mid-1960s.

• Discrete transistor — the second-generation device. It is solid-state, but each unit is still a separate component wired in one at a time, so it precedes the third generation rather than defining it.

• Microprocessor — an entire CPU on one chip (Intel 4004, 1971), which marks the fourth generation. A “macroprocessor” is something else again: a macro-expansion program, not a circuit-building technology.

Result: the third generation of electronic computers is built on integrated-circuit (IC) technology.