WPA was designed to replace WEP (the earliest Wi-Fi protection method) whereas WPA2 was designed as a replacement for WPA. With the evolution of wireless technology came problems related to security of personal data and information. It was very easy for hackers to break into a WEP protected Wi-Fi network. WPA made it relatively difficult but there still remained bugs that needed attention. For this reason, network security experts designed the WPA2 protection method.
Due to fairly simple algorithm, WPA uses relatively low amount of processing power while WPA2, which has a much more complex algorithm, requires much more processor resources to secure your wireless network.
The protection levels offered by each of these methods also differs. Hacking into a WPA secured network is much easier than hacking into a WPA2 protected wireless network.
The message integrity check algorithm used in WPA is called ‘Michael’ and supports TKIP (Temporal Key Integrity Protocol) encryption while the security algorithm used in WPA2 encryption is called AES (Advanced Standard Encryption).
All access points, old or new are capable of operating with WPA method. However, the same is not true as far as the WPA2 method is concerned. Most of the old access points need a firmware upgrade before they can operate with WPA2 encrypted wireless networks.
Last but not the least, you will never notice high network loads with WPA. However, the case may be opposite with WPA2 especially if you are using old firmware. If that happens, you may have to invest in purchasing new access points.