In a hub, a frame is passed along or "broadcast" to every 
one of its ports. It doesn't matter that the frame is only 
destined for one port. The hub has no way of distinguishing 
which port a frame should be sent to. Passing it along to 
every port ensures that it will reach its intended 
destination. This places a lot of traffic on the network 
and can lead to poor network response times. 

Additionally, a 10/100Mbps hub must share its bandwidth 
with each and every one of its ports. So when only one PC 
is broadcasting, it will have access to the maximum 
available bandwidth. If, however, multiple PCs are 
broadcasting, then that bandwidth will need to be divided 
between all of those systems, which will degrade 
performance. 

A switch, on the other hand, keeps a record of the MAC 
addresses of all the devices connected to it. With this 
information, a switch can identify which system is sitting 
on which port. So when a frame is received, it knows 
exactly which port to send it to, which significantly 
increases network response times. And, unlike a Hub, a 
10/100Mbps switch will allocate a full 10/100Mbps to each 
of its ports. So regardless of the number of PCs 
transmitting, users will always have access to the maximum 
amount of bandwidth. It's for these reasons

switch operates on data link layer.
hub operates on physical layer only.