The Backbone is normally only used to connect the servers. The Workstations/Users would then run the connection off the servers separate ports. This requires a little more work in the configuration, but provides much greater process speed and greatly limits possible network problems.
Example:
In the Planned configuration, each computer labs would have a 100MB connection divided among the 20 or so computers. This would also be a private connection for those machines.
Since the connections would directly to the server containing the data, the server could put out up to 800MB of Data. Additionally, since only 20 computers are on each connection, the possibility of collisions is greatly reduced.

In comparison:
The Current setup has everyone running on a single 100MB connection. This means that the 100MB connection is divided among the 140 computers in D-Wing. The possibities of collisions is also much greater. The use of a switch doesn't help since all the traffic goes to either the Server or the Internet. Switches improve performance when setup with multiple sources of data.