Today in class I was watching my teacher and student splicing 3 Ethernet cables together. One went to the router, one went to one PC and the other to another PC. I didn't think that was possible, but it did work however it was terribly slow. I would have figured it acted as sort of like a hub. Why did this work?

I'm thinking it was just a "Y" cable with the 2 pc ends wired null in parallel.

just thinkin'
GV

Three ends shouldn't work, or in this case caused huge amounts of errors such that it barely worked. You can use a three end cable with the extra end wired to "monitor" one, but not both, of the other two computers. Useful for sniffers.

Four would be fine if wired properly. Basically you wire it like two separate cables, two pairs each. Won't work for gigabit.

Well all I saw is them remove the Ethernet cable from the wall jack strip each wire of the 4 pairs. Then take 2 other Ethernet cables (one about 3 inches and the other went back up and dropped down to another PC about 5 feet away) and twist all the like colors together and put some tape on it, then added a new jack to the short 3 inch cable and connected that too another PC.

i have seen this done but it aint reliable

It would cause a lot of collisions. therefore would be real slow.