Cisco PIX:

Is a dedicated hardware firewall appliance
Act as a  Stateful packet filtering firewall.
Use  PIX operating system similar in interface  to Cisco IOS .
Use  PIX Device Manager (PDM) for a graphical interface.
Provide  stateful firewall protection and IP Security (IPSec) VPN capabilities
To ensure the security PIX use inside interface , outside interface etc concepts

Cisco ASA:

Is firewall and [...]