Dr. Scott M. Baker Reaches Back Into Microprocessor History to Design an Intel 4004 SBC
Period-appropriate single-board computer design pays homage to Intel's four-bit 4004 — with a few modern quality-of-life additions.
Vintage computing enthusiast Dr. Scott M. Baker has designed a single-board computer that reaches right back into the earliest days of microcomputing — picking Intel's first commercially-released microprocessor, the 4004, as its heart.
"I’ve previously done projects using the [Intel] 8008, the world's first commercially available 8-bit microprocessor, and I've always wanted to do some projects using the 4004, the first commercially available microprocessor (dropping the '8-bit' qualifier; the 4004 is 4-bit)," Baker explains of the project. "I'm saying 'commercially available,' because as one reader points out, there was a classified navigation computer for the F-14 fighter airplane that preceded the 4004."
Intel's 4004 was launched back in 1971, and is generally recognized as the first commercially-successful microprocessor built using large-scale integration (LSI). Its success, though, was not found in the contract for which it was designed — the creation of a chipset to drive a printing calculator from Busicom — but as the first in what would become Intel's x86 architecture and the company's rise to one of the biggest names in computing.
Baker's single-board computer — which accepts either an original Intel 4004 or compatible or its 1974 successor the Intel 4040, which Baker notes "is certainly a lot less expensive" — is based on a design from Jim Loos and is built primarily around period-appropriate components, including 74-series logic chips and an Intel 4289 Standard Memory Interface designed to adapt the chip's four-bit address bus to an eight-bit equivalent for compatibility with standard read-only memory (ROM) modules.
The design also includes a few improvements over what an original Intel board may have looked like: the 4004's 4kB ROM space is expanded to 16kB with four-bank paging, there's a choice of "bit-banged" CPU-driven or hardware serial interfaces, Multimodule expansion, and an RC2014 bus interface — adapted to the four-bit processor through the use of a peripheral interface chip. Finally, there's room for up to a generous — by the standards of the time, at least — 320 bytes of RAM, a four-bit LED display, and four DIP switches for input.
Schematics and Gerber board files for the project have been released on GitHub under an unspecified license; Baker's write-up is available on his website.