Preface#

Modern digital hardware is easy to use without understanding. A logic gate, a flip-flop, a lookup table in an FPGA — all can be dropped into a design as black boxes that simply behave. But the shape of those black boxes is not arbitrary. Every one of them carries the fingerprints of the technology it replaced and the constraints that technology lived under.

This notebook exists to make that lineage visible.

It is not a textbook and not meant to be read strictly front to back, though it does follow a rough progression — from the earliest physical representations of discrete state, through the component families that industrialized logic, to the integrated and programmable forms in use today. The emphasis is less on cataloging devices than on the reasoning that connects them: what each era was trying to solve, what it gave up to get there, and which ideas proved durable enough to survive into the next generation.

A few things recur at every layer, regardless of the underlying technology. The distinction between combinational and sequential behavior. The role of state and how it is stored. Timing, and what happens when signals arrive later than assumed. Abstraction, and the moments when the layer beneath reasserts itself. Recognizing these across relays, tubes, transistors, TTL, CMOS, and programmable logic is the real subject — the specific devices are examples, not the point.

This material is written primarily as a working reference, structured so that others can follow the same thread. Everything here is for educational and reference purposes. Where the history is compressed or simplified, it is in service of the through-line rather than exhaustive accuracy, and details worth verifying should be verified against primary sources.

Some portions are developed with the assistance of modern AI-based tools used as research aids and writing accelerators. These tools help with structuring ideas, surfacing connections, and improving clarity — but they are not authorities. Not all content has been independently verified in every context, and errors or omissions are possible. Final judgment and responsibility rest with the human reader — and with me as the author.

This is one volume in a set of engineering notebooks. It shares its voice and structure with its siblings, and it assumes the reader would rather understand why digital logic looks the way it does than simply memorize how a given part is wired.

— Chris Deever