What is the difference between decentralized and distributed systems?
“Given a random piece of tech, the first question is not how does it work, but what does it do.”
“The difference is subtle and moreover:
A decentralized system is a subset of a distributed system.
The primary difference is how/where the “decision” is made and how the information is shared throughout the control nodes in the system.
Decentralized means that there is no single point where the decision is made. Every node makes a decision for it’s own behaviour and the resulting system behaviour is the aggregate response.
Think of groups of humans for this:
· We all make decisions (constrained to be sure) but our decisions influence the decisions of all around us until we get “large” system level behaviour (e.g. capitalism).
· A key characteristic is that typically no single node will have complete system information.
(For an example of decentralized applications, read the post on Coindesk.)
Distributed means that the processing is shared across multiple nodes, but the decisions may still be centralized and use complete system knowledge. (For an example of a distributed ledger read this post on Coindesk. )
Swarming algorithms are typically decentralized to increase the robustness of the system; but even some of them have a “leader” that all others must follow.
Some control algorithms I’ve seen for multiple quad-copter control are purely distributed in that a central over-seer gives optimization problems to each copter to solve then return the solution. The over-seer will then issue commands based on the aggregate result.
Here’s a philosophical question: if the over-seer is “voted” into office by the nodes, is it decentralized or centralized? I’d have to say decentralized, but it is arguable.”
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