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An Ethernet hub is – well, Wikipedia does an impeccable job of summarizing what it is:

An Ethernet hub, active hub, network hub, repeater hub, multiport repeater, or simply hub is a network hardware device for connecting multiple Ethernet devices together and making them act as a single network segment. It has multiple input/output (I/O) ports, in which a signal introduced at the input of any port appears at the output of every port except the original incoming.[1] A hub works at the physical layer (layer 1) of the OSI model.

To which may be added, that hubs come into the picture with the movement from the pure bus topology of the original Ethernet, to the star topology used in later years, so they postdate Ethernet itself.

And I'm wondering to what extent did the falling price of the electronics that would go into a hub, influence the timing of the switch from bus to star topology.

What was the first Ethernet hub?

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    There were multiport repeaters for thinwire; I think these were logically the same as 'hubs', which is more of a twisted-pair term. The result is a tree topology, not a simple star. Nov 13 at 4:00
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    Also for thickwire, which I had forgotten until @Jens triggered my memory. See my answer. Nov 13 at 13:41
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    @another-dave Repeaters are entirely different from hubs. See my comment on your answer for more details.
    – cjs
    Nov 13 at 14:01
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    I'd say Wikipedia does a far from "impeccable" job since, in Ethernet terminology a repeater is something entirely different from a hub: it forwards packets between two separate layer 1 networks.
    – cjs
    Nov 13 at 15:30
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Following on from the answer from Jens, but with specific DEC information.

I don't know about 'first', but the DELNI from DEC was a multiport Ethernet device for 'thickwire' installations.

You could connect it to a standard cable, where it would provide access for 8 systems; use it standalone, for a small "ethernet in a box"; or cascade them for more systems. The documentation suggests only two levels were possible; I assume this is because there's some propagation delay that would interfere with collision detect.

Per Computer History Museum,

A DELNI is a fan-out box that goes in a thickwire network between a transceiver (which connects to the female D-shell on the DELNI) and up to eight computers. These devices allowed DEC computers to be combined into Local Area and Inter Networks. The more common name for a DELNI today is 'hub.'

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    This doesn't answer the question because a repeater is entirely different from a hub. A hub connects multiple stations together into the same physical-layer network (CSMA/CD domain). A repeater connects two separate physical-layer networks, action as a station on each. Two stations on either side of a repeater can transmit at the same time and will never collide because they are actually on separate networks.
    – cjs
    Nov 13 at 14:00
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    Perhaps this is a matter of terminology. A DELNI connects multiple stations into a single network. It is not possible for two stations (either upstream or downstream) to transmit at the same time. A quick scan of the DELNI manual shows that DEC did not use the word 'repeater', so maybe that's my error. I will remove the word. Nov 13 at 14:31
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    Yes, if two stations connected through a DELNI could collide, it was not a repeater. "Repeater" is a term of art in the Ethernet world that specifically indicates a device that transfers packets between two separate layer 1 networks. (Though, perhaps confusingly, all these layer 1 networks may be part of a single layer 2 network.)
    – cjs
    Nov 13 at 14:36
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    @cjs Sorry but you appear to be confused. A repeater connects two physical networks (e.g thickwire and thinwire) into the same CSMA/CD domain. A thing that acts as a station on multiple networks would be a bridge or router.
    – richardb
    Nov 13 at 16:22
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    Ah, actually you're right; I was for some reason confusing repeater and bridge. Sorry about that.
    – cjs
    Nov 13 at 16:29
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As for the main question "what was the first Ethernet hub?", I cannot answer this, but my guess would be "multiple vendors came out with multiple hub models at the same time". See below for the reasoning.

But I lived through the transition from a thick ethernet bus-topology to a tree-topology in the department of my university, so I can tell you that yes, price very much paid a role, and also we made the transition not to hubs replacing the bus, but to switches (or a mix of switches and hubs, I don't remember the details) replacing the bus. Because hubs cause contention in the complete network, while switches keep this more locally. And since there's a lot more electronic in switches, price is even more important.

And I would assume that we were not the only ones who did it that way.

That said, the concept of a "network hub" predates ethernet hubs.

Before Ethernet, there were token-based networks, and for example one of them, ARCNET, used really cheap passive unpowered hubs. Which were actually mandatory, it didn't have a bus topology.

So the concept was well known, which is why I think you'll have a hard time pinpointing the "first" Ethernet hub, and when hubs were included in the standard, very likely multiple models were offered by multiple vendors. There may have been a proof of concept hub in some lab somewhere before it became part of the standard, but again, it'll be difficult to find out any details on that.

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    Also, the concept of a repeater is a really obvious one, and the concept of a repeater that also duplicates is a simple step. Nov 13 at 9:13
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    Ethernet hubs are, at least conceptually, rather different from Arcnet hubs since they must do something no token ring system needs to do: join all of the stations to a medium suitable for CSMA/CD or, essentially, behave like a system where all stations are connected to points along a single terminated transmission line.
    – cjs
    Nov 13 at 13:57
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    @cjs yes, they are different in what they need to do technically. But the concept itself (provide a split-off point) was already well known - you "just" had to figure the technical differences. The problem with all those "what was first" questions is that inventions don't spring full-formed into life from nothing, they are in the majority of cases iterations and improvements and re-applications of concepts that have been floating around and the time they were invented. So "how did this came to be invented" is much more interesting than "what was first". At least to me.
    – dirkt
    Nov 13 at 14:07
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    As someone who was a precocious kid ordering 3Com catalogues from 1-800 numbers and the like, I can elaborate on this a bit. Before switches were economical for anything but specialist applications, there were "bridges" to solve the contention issue... basically, a switch is a multi-port bridge or, conversely, a bridge is a two-port switch intended as a more cost-effective way to limit contention by breaking a network into smaller segments.
    – ssokolow
    Nov 13 at 14:21
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    @dirkt No, the concept itself is entirely different, though it may appear the same to the naïve observer. The whole point of an Ethernet hub is that it doesn't actually change the topology. Ethernet hubs and switches/etc. are as similar as balloons and aeroplanes.
    – cjs
    Nov 13 at 14:34
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Probably the slightly weird DELNI, which allowed multiple nodes to share one thickwire tap came out before but thinwire Ethernet (802.3a) and repeaters (802.3c) were both added to the Ethernet standard in 1985.

DEC's classic 8 port thinwire + AUI DEMPR came out in 1986, and a cutdown 1 thinwire + 1 AUI version (DESPR) in 1987. The latter initially retailed for $875.

Possibly others were slightly earlier and/or cheaper but that's about the right ballpark.

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The first "hub" I saw was a multiport AUI connector. Probably less to save money, as they were expensive, too. But they reduced the risk of doing anything bad to the vampire clamps on the yellow cable (10BASE5).

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