Intel 8080

The Intel 8080 is a seminal CPU introduced in 1974 that gave rise to the personal computer/home computer/microcomputer revolution.

It was integrated in early home computers like the Altair 8800, the Interact Home Computer, the DAI Personal Computer, and arcade systems like the Taito 8080 and Midway 8080.

The 8080 is often said to be the "first truly usable microprocessor". Its predecessor, the first 8-bit microprocessor Intel 8008, had a rigid seven-level address call stack instead of a flexible Stack Pointer. The 8008 instruction set is itself based on the CPU board of the Datapoint 2200 computer. Despite what its naming suggests, the Intel 8008 is totally unrelated to the Intel 4004.

Fun fact: the microprocessor isn't really an invention, but rather something that everyone knew would happen, and it was just a matter of waiting for the technology and market to be correct.

It was obvious in the late 1960s that a CPU board, built out of dozens of TTL chips, would eventually be put on a single chip. And it was just a matter of time for the density of MOS chips to improve to the point that it was practical. Source

The 8008 was built with PMOS circuitry, while the 8080 was built with NMOS, which provided much superior performance.

NMOS became the standard microprocessor technology until the rise of CMOS in the 1980s, combining NMOS and PMOS to dramatically reduce power consumption.

The 8080 is not binary-compatible with the 8008 because almost all the instructions were shifted to different opcodes.

One important but subtle change was that the 8 register/memory codes were reordered to start with B instead of A. The motivation is that this gave registers in a 16-bit register pair (BC, DE, or HL) codes that differ only in the low bit. This makes it easier to specify a register pair with a two-bit code.

CP/M required an 8080, 8085 or Z80 CPU and between 1976 and about 1983, microcomputers with a Z80 that ran CP/M were the norm before the market shifted to MS-DOS.

The 8080 ultimately led to the machine code-compatible, but more powerful clone Zilog Z80, which was of course also used in the Amstrad CPC and Sinclair ZX Spectrum among others. (Note that 8080 assembly language looks different from Z80 mnemonics; e.g. the Z80 uses LD whereas the 8080 has MOV and several other commands.)

Meanwhile Intel produced the 8085, an improved, backward-compatible version of the 8080, with refinements to power consumption and integration.

See: Notes on PLA Inside the ALU Instruction set: the octal table Register file Flag circuits The ALU and its hidden registers Decimal adjust circuitry 8085 CPU reverse engineered

• Intel 8080 at the English-language Wikipedia
• Intel 8080A datasheet
• 8080 assembly language programming manual
• 8080 Systems User's Manual Contains a detailed breakdown of machine cycles
• Mapping between i8080 and Z80 mnemonics
• 8080 opcode map
• 8080 CPU Exerciser
• Oral history collection: Intel 8080