The the late 1960s and early 70s, there was much talk about "generations"
of computer technology. This photo illustrates what were commonly known
as the three generations:
First generation: Vacuum tubes (left).
Mid 1940s, beginning with ENIAC. IBM pioneered the
arrangment of vacuum tubes in pluggable modules such as the one shown in the
photo. The IBM 650 (1953) was a first-generation
computer, as were the pioneering IBM one-off
SSEC (1948) and NORC (1954),
both built by Columbia University's Watson Lab.
Second generation: Transistors (right). 1956. The era of
miniaturization begins. Transistors are much smaller than vacuum tubes,
draw less power, and generate less heat. Discrete transistors are soldered
to circuit boards like the one shown, with interconnections accomplished by
stencil-screened conductive patterns on the reverse side.
The IBM 7090 was a second-generation computer.
Third generation: Integrated circuits (foreground), silicon chips
contain multiple transistors. 1964. A pioneering example is the ACPX
module used in the IBM 360/91, which, by stacking
layers of silicon over a ceramic substrate, accommodated over 20 transistors
per chip; the chips could be packed together onto a circuit board to achieve
unheard-of logic densities. The IBM 360/91 was a hybrid second- and
Other generations were to follow: the fourth (1971-1980) based on Very Large
Scale Integrated (VLSI) circuits such as the Digital Equipment Corporation
DECSYSTEM-20, and the
IBM PC and PC/AT.
And then a fifth based on Ultra Large Scale Integration (ULSI) and parallel
processing (21st Century laptops, notebooks, tablets, etc). And then
whatever else comes next,
computers. In any case, at this point (2021) the average cell phone or
"smart watch" has more memory and computing power and speed than our
third-generation IBM 360/91 did, which sold for millions of dollars and
occupied acres of floor space.