Excessive Network Collisions?

[overpower]

Ok I'm writing this cause I've seen two contradictary responses to whether excessive collisions in a 10mbit network is normal or not.
First off what exactly causes a collision?
From what I've heard a collision is when two packets are sent into a port at the same time.
Secondly, when are collisions too excessive? Currently I'm getting told that two of my NetGear 10/100 nics
are having 400 collisions a second according to the schools routers. Of course this is only during a sustained file transfer.
I was wondering if collisions could be caused by cables/nics/operating systems/ etc. I've tried multiple nic/cable solutions and I've even switched physical ports on the school's router.
Thanks in advance.
Alan

 

[Norssak]

Collisions happen when 2 nodes on the same segment try to transmit at the same time. This is a natural statistical occurrence. The more nodes per segment, the more collissions will occur. So the fact that collisions are occurring is nothing to worry about. If you are getting too many collisions, such as if you have 24 port Hub, then you get a 24port switch, now there are no collisions (as long as fullduplex is enablabled)

 

[Ender78]

Alan,

How far apart are the machines (worst case scenario) at the school. 400 collisions per second is pretty bad (chances are that you are suffering from VERY bad network speeds as a good portion of the network is inaccessible during those colisions [for those that want to nitpick this statement please do so, I am trying to make the explanation as easy as possible]). I have alos een a really cheap or old hub to be problematic? 400 collisions per second is definately not normal !!!! Colisions cannot be avoided on a non switched network. I would also try to look at the statistics, and unplug one machine at a time (lets say for a minute). One bad network card could be killing your entire network.