In the 1970s, as integrated circuit manufacturers were able to fit larger numbers of transistors on a single chip, single chip computers were introduced, by intel, motorola, and their competitors.
These chips would have a full, but small, set of control and data registers, and circuitry to decode and execute instructions.
The intel 4004, which had registers only four bits wide, is the lineal ancestor of intel's Pentium family of computer chips. The intel 4004, and its rivals, used only a few thousand transistors.
By 1993, when the first computers in the Pentium family of computer chips were introduced, single chip computers incorporated millions of transistors.