All Pixen are just pcs. They all have intel cpus.
You can build your own pix 520 with a certain intel motherboard and intel nics. The problem is that buying the 16MB flash card to run PIX OS > 5.2, IIRC, is 800ish US. The total cost of the project would be more than a used 501 or 506. A pix 520 with the 2MB flash card cannot run any pix os from the last 18+ months. Caveat Emptor
The appeal is building a frankenpix (the community name for em) is for people who want to play with > 2 interfaces and failover, if they are hardcore about studying for the CCSP or Cisco Firewall Specialist designations.
Cisco has not taken a dim view of hobbyists creating these. If you were to use one in a production business network however, they would probably come to your house, rough you up and rearrange your furniture.
