Central Processing Units

The Intel corporation designed the 8 bit 8080 microprocessor as an enhancement to its earlier 8008 microprocessor.  The chip was introduced in April of 1974.  The 8080 had 8 general purpose registers, each 8 bits, a 16 bit program counter, and a 16 bit stack pointer.  The processor supported a maximum of 64K of combined data and program memory.  The chip contained 6,000 NMOS transistors, produced with a 6 micron resolution, and ran at a clock speed of 2 MHz.  The 8224 clock generator and 8228 system controller were normally used with the 8080.  The first personal computer, the Altair, was based on the 8080. 

Clones of the 8080 were produced by Texas Instruments, National Semiconductor, AMD, Signetics, OKI, Tesla, Siemens, NEC, and Mitsubishi. 

Two years later, in 1976, Intel introduced the 8085 processor.  The 8085 was an improved version of the 8080: the instruction set was upward compatible (two instructions were added, and the interrupt structure was enhanced.  The chip also incorporated the functions of a clock generator and system controller, simplifying implementation.  This increased the chip count to 6,500, but the chip was smaller due to the use of a 3 micron process.  The 8085 was also easier to use because it required only 5 volt power (the 8080 required +5, +12, and -5 volt power.)