In 1975 AMD introduced the Am2901 and Ken Shirriff takes a look inside. This chip was a type of processor called a bit-slice processor: each chip processed just 4 bits, but multiple chips were combined to produce a larger word size. This approach was used in the 1970s and 1980s to create a 16-bit, 36-bit, or 64-bit processor (for example), when the whole processor couldn’t fit on a single fast chip.

The Am2901 chip became very popular, used in diverse systems ranging from the Battlezone video game to the VAX-11/730 minicomputer, from the Xerox Star workstation to the F-16 fighter’s Magic 372 computer.3 The fastest version of this processor, the Am2901C, used a logic family called emitter-coupled logic (ECL) for high performance.

In this blog post, Ken opens up an Am2901C chip, examines its die under a microscope, and explains the ECL circuits that made its arithmetic-logic unit work.

See the blog post for all the details.