1970s and 80s: The Intel 4004 Team, Zilog, And The Importance of Backwards Compatibility

The Intel 4004 was the world’s first commercially produced microprocessor, it was a 4-bit CPU on a single chip. Federico Faggin was the leader of the project, and the lead for the 4004’s successors: the 4-bit 4040 and the 8-bit 8008 and 8080. But in 1974 Faggin became frustrated with working at Intel, left and founded his own startup Zilog along with his Intel colleague Ralph Ungermann; they were later joined by fellow colleague Masatoshi Shima. Zilog then released the Z80, which was software compatible with Intel’s 8080, cheaper, and had a number of improvements; the Z80 was very successful for these reasons. A variant of the Z80 was later used in the original Nintendo Game Boy.

Following on from the 8-bit Z80’s success, Zilog released the 16-bit Z8000 in 1979… which was not as successful, for several reasons:

• It was released a year after Intel’s 16-bit CPU, the 8086, which was source compatible with the 8080, allowing software to be ported from the 8080 to the 8086 very easily.
• The Z8000 was not compatible with any other processor, not the Z80 nor 8086, so old software could not be easily ported.
• The Intel 8088, a cheaper version of the 8086, was released a few months after the Z8000, and was used in the original IBM PC, which took the world by storm.
• The 32-bit Motorola 68000 was released a few more months after the Z8000, and was much faster.

Much later in 1986 Zilog released the 32-bit Z80000, which was software compatible with the Z8000, but it wasn’t enough to save the series. After that Zilog left the high performance CPU race and refocused on the microcontroller market.

The Zilog story is a lesson in the importance of backwards compatibility and time to market. A key to Intel’s success has always been backwards compatibility: their main line of processors, the 8008, 8080, 8086, 8088, 80286, extending to the present day, support software written for their immediate predecessor with none or little porting by software developers, whereas all Intel’s projects that didn’t have backwards compatibility, like the iAPX 432, i960, i860 and Itanium, all failed. Time to market is also very important: although the Z8000 was much faster than the 8086, the 8086 had nearly a year head start in gaining popularity and software, and the even more powerful 32-bit Motorola 68000 released only months after the Z8000. This left the Z8000 in an awkward nowhere land: if you wanted to easily port your existing 8080 or Z80 software, the 8086 was attractive, and if you wanted very high performance, the 68000 was attractive. For all these reasons the 8086 and the 68000 both became very successful, and the Z8000 did not.