The Intel 8080 is an early 8-bit CPU, released in April 1974 running at 2 MHz, and is generally considered to be the first truly usable microprocessor CPU design.
It is the successor to the Intel 8008, with which it was assembly language source-compatible because it used the same
instruction set developed by Computer Terminal Corporation. The 8080's 40 pin DIP packaging permitted it to provide a 16-bit address bus and an 8-bit data bus,
allowing access to 64 kilobytes of memory. It has seven 8-bit registers (six of which could be combined into three 16-bit registers),
a 16-bit stack pointer to memory (replacing the 8008's internal stack), and a 16-bit program counter.
The 8080 had 256 I/O ports allowing I/O devices to be connected without the need to allocate memory space - as is required for memory mapped devices -
but at the expense of having programmers deal with separate I/O instructions. The first single-board microcomputer was built on the basis of the 8080.
The 8080 was used in many early computers, such as the MITS Altair 8800 and
IMSAI 8080, forming the basis for machines running the CP/M operating
system (the later, fully compatible and more capable, Zilog Z80 processor would capitalize on this, with Z80 & CP/M becoming the dominant CPU & OS combination
of the period much like x86 & MS-DOS for the PC a decade later).
Shortly after the launch of the 8080, the Motorola 6800 competing design was introduced, and after that,
the MOS Technology 6502 clone of the 6800.
At Intel, the 8080 was followed by the compatible and electrically more elegant 8085, and later by the assembly language compatible 16-bit
8086 and then the 8/16-bit 8088, which was selected by IBM for its new PC to be launched in 1981. The 8080, via its ISA, thus got a lasting impact on computer history.
The 8080 was very popular and was second-sourced by various manufacturers. Clones of the 8080 were also made in
former Eastern Block countries like USSR, Poland, CSSR, Hungary and Romania.
Versions and speed:
8080/8080A: 2.0 MHz
8080A-1: 3.125 MHz
8080A-2: 2.67 MHz