The Intel 4004 was a 4-bit

4-bit

The Intel 4004, the world's first commercially available single-chip microprocessor, was a 4-bit CPU. The F-14 Tomcat's Central Air Data Computer was created a year before the 4004, but its existence was classified by the United States Navy until 1997...

 central processing unit

Central processing unit

The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...

 (CPU) released by Intel Corporation in 1971. It was the first complete CPU on one chip, and also the first commercially available microprocessor. Such a feat of integration was made possible by the use of then new silicon gate technology allowing a higher number of transistors and a faster speed than was possible before.
The first public mention of 4004 was an advertisement in the November 15, 1971 edition of Electronic News, though unconfirmed reports put the date of first delivery as early as March 1971.