Before Blockchains, There Was State Machine Replication

July 13, 2026

AI Summary

5 min read

Barbara Liskov, a Turing Award winner whose work on data abstraction and distributed systems shaped modern computing, spent the 1970s developing the programming language CLU to support modular programming. By the early 1980s, she felt she had done as much as she wanted in programming languages and was looking for a new challenge. She read a paper by Bob Kahn describing the dream of distributed computing—programs with components running on different nodes in a network, communicating with each other—and realized nobody knew how to build them. That became her next problem.

From Guardians to Ledgers: The Argus Language and Viewstamped Replication

Liskov’s first distributed systems project was a programming language called Argus, an extension of CLU. Argus introduced a new kind of object called a guardian, which resided at one node of a network and provided operations that could be called from other nodes. A distributed program consisted of many guardians, each running on its own node, communicating with each other. This was not a clean break from her earlier work—it was a continuation that added concurrency and, crucially, failure handling. Argus used atomic transactions and a two-phase commit protocol to ensure that computations spanning multiple nodes either completed fully or had no effect at all.

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What you'll learn

1 (00:00) **Introduction: The Problem of Malicious Attacks** - Barbara Liskov recounts how DARPA's interest in handling malicious attacks led her and student Miguel Castro to develop Practical Byzantine Fault Tolerance (PBFT).
2 (01:50) **Episode Setup: State Machine Replication & Blockchains** - Hosts Tim Ruffing and Ty Abraham introduce the episode's focus on the foundational computer science behind blockchains.
3 (02:56) **Origin Story: From Programming Languages to Distributed Systems** - Liskov explains her pivot from programming languages (CLU) to distributed systems around 1980.
4 (04:53) **The Argus Language: Guardians, Concurrency, and Failures** - Liskov describes how Argus tackled concurrency and failures in a distributed setting.
5 (07:29) **Modularity: The Link Between Theorems and Programs** - Liskov draws a parallel between modular programming and proving theorems.
6 (09:00) **Motivation for Viewstamped Replication: The Replicated File System** - The initial motivation was a practical one: building a replicated file system to avoid file transfers and downtime.
7 (12:15) **Viewstamped Replication: The Protocol and the "Ledger"** - Liskov and student Brian Oki developed Viewstamped Replication to solve the "embarrassing pause" problem in two-phase commit.

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Show Notes

Every blockchain today relies on replication techniques first developed in the 1980s by researchers who weren't thinking about cryptocurrencies at all.

In this episode, Tim Roughgarden speaks with MIT professor and Turing Award winner Barbara Liskov, one of the pioneers of programming languages, fault tolerance, and distributed systems. Joined by a16z crypto research partner Ittai Abraham, they trace the evolution of ideas that now underpin modern blockchain networks.

The conversation explores viewstamped replication, Practical Byzantine Fault Tolerance (PBFT), state machine replication, and why concepts developed decades before Bitcoin became the foundation for today's blockchain protocols. Along the way, Liskov reflects on the relationship between theory and practice, the importance of modularity and formal reasoning, and why AI is creating a new generation of systems research.

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