This can't be overemphasized. Both 10BASE5 and 10BASE2 were a "shared medium". Everyone connected to the same cable. It really was "an absolute nightmare" to debug.
There were no hubs and/or switches to isolate users from each other.
I don't know if they existed in the early days, but when 10Base-T got popular both hubs & switches would often have a 10Base-2 segment interface or two as well.
I'm fairly sure there was some possibility of segment isolation, because people thieving BNC terminators (seriously, they're like crack to schoolkids, along with mouse-balls) would drop off chunks of the network, but not the entire thing.
I guess it could have just been multiple NICs in the server, though.
I'm fairly sure there was some possibility of segment isolation
This discussion seems to have died off, but here's some stuff I dug up mostly from Wiki (it's been so many years since I was directly involved with any of it):
10BASE5 could be a max length of 500 meters
and have up to 100 nodes
The 10BASE5 cable must be one linear run;
T-connections are not allowed.
10BASE2 could be a max length of 185 meters
and have up to 30 nodes
So there was need for some "segment isolation" as you call it. A single Ethernet would have multiple segments (all activity fully visible on all segments), because given the restrictions on physically routing the network cables around, it wasn't possible to connect everyone in even a relatively small building to a single segment. E.g. 185 meters isn't much when it has to be snaked around the backs of desks and around the perimeters of rows of cubicles.
There were devices called "repeaters" (originally very dumb two-port amps/isolators) that would connect segments of the same Ethernet. IIRC you could even connect a 10BASE5 segment to a 10BASE2 segment.
You were limited to how many segments you could have overall, and limited in overall distance to IIRC about 1500 meters for pure 10BASE5. Every packet was visible everywhere else, it was all a single "collision domain". The distance limitation had to do with all devices needing to observe a collision within a certain amount of time (active transmitters were monitoring the wire to see if any other packet collided with theirs). CSMA/CD protocol meant all active transmitters would stop sending and "back off" an exponentially increasing random amount of time when they detected a collision.
Combine all that with "quirky" Ethernet controller chips for even more fun.
I sure don't miss any of that. Thankfully those memories have faded over time.
This can't be overemphasized. Both 10BASE5 and 10BASE2 were a "shared medium". Everyone connected to the same cable. It really was "an absolute nightmare" to debug.
There were no hubs and/or switches to isolate users from each other.