here is an example to explain my incomprehension: PING: PC1 -----> SWITCH -------> PC2.
i know that when a PC1 send frame to switch, the switch will add the mac address to his mac address table, then it will diffuse the frame to all the PCs including PC2. PC2 respond to switch (because the message is refer to him) and the switch the mac address of PC2 to his mac address table.
PC1 -----> SWITCH -------> PC3.
now, when PC1 send frame to Switch. do switch diffuse the frame to all the PCs including PC2, OR it diffuse to all the PCs without PC2 since switch knows the mac address of PC2.