“As you can see, the 1970s were a time of large changes in semiconductor chip technology. The 4004 and 8008 were created when the technological capability intersected with the right market.”
Ken Shirriff shows how he got Die photos and analysis of the revolutionary 8008 microprocessor, 45 years old.
This chip, Intel’s first 8-bit microprocessor, is the ancestor of the x86 processor family that you may be using right now. I couldn’t find good die photos of the 8008, so I opened one up and took some detailed photographs. These new die photos are in this article, along with a discussion of the 8008’s internal design.
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The 8008’s complicated story starts with the Datapoint 2200, a popular computer introduced in 1970 as a programmable terminal. (Some people consider the Datapoint 2200 to be the first personal computer.) Rather than using a microprocessor, the Datapoint 2200 contained a board-sized CPU build from individual TTL chips. (This was the standard way to build a CPU in the minicomputer era.) Datapoint and Intel decided that it would be possible to replace this board with a single MOS chip, and Intel started the 8008 project to build this chip. A bit later, Texas Instruments also agreed to build a single-chip processor for Datapoint. Both chips were designed to be compatible with the Datapoint 2200’s 8-bit instruction set and architecture.
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The Datapoint 2200’s architecture was used in the TMC 1795, the Intel 8008, and the next version Datapoint 220011. Thus, four entirely different processors were built using the Datapoint 2200’s instruction set and architecture. The Intel 8080 processor was a much-improved version of the 8008. It significantly extended the 8008’s instruction set and reordered the machine code instructions for efficiency. The 8008 was used in groundbreaking early microcomputers such as the Altair and the Imsai. After working on the 4004 and 8080, designers Federico Faggin and Masatoshi Shima left Intel to build the Zilog Z-80 microprocessor, which improved on the 8080 and became very popular.
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A key innovation that made the 8008 practical was the self-aligned gate—a transistor using a gate of polysilicon rather than metal. Although this technology was invented by Fairchild and Bell Labs, it was Intel that pushed the technology ahead.
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While the 8008 wasn’t the first microprocessor or even the first 8-bit microprocessor, it was truly revolutionary, triggering the microprocessor revolution and leading to the x86 architecture that dominates personal computers today.
The legacy of the Datapoint still exists in the Intel ‘little-endian’ architecture and parity flag being two examples cited. Those engineering decisions were in an era long gone. They have been subsumed in newer technologies and newer circuit and component innovation. It took 6 years (to 1978) from the 8008 to break into the personal computer era with the Apple II and the TRS 80 and the many other ‘cpu on a chip plus a whole lot of glue circuits on a board’ personal computers. 6 years after than (~1984) and the IBM PC tackled the business world and the 80286 showed up. 6 years after (~1990) that and megabyte working memory sizes showed up with the 80386 to manage it. Another 6 years (~1996) and the I’net started pushing. By 2002, the modern PC era was well under way with networking, sound, mutli-tasking operating systems, gigahertz clock speeds, gigabyte working memory sizes, 64 bit CPU’s, and on and on.
Now, even a cheap cell phone has a GHz clock speed, a gigabyte of working memory, and 8 GB of non-volatile memory. And a high resolution color display and many sensors and capabilities not seen in any consumer computer even ten years ago … not to mention the network infrastructure that supports it. And the cell phone is a common as dirt Christmas present, even for kids.
Merry Christmas!