Cisco - Cisco PIX Firewall Release Notes, Version 6.3(5)
Cisco - Upgrade Software for PIX 500 Security Appliance 6.x to 7.x
The Cisco PIX 500 Series Security Appliances has been retired and is no longer supported.
End-of-Sale Date: 2008-07-28
End-of-Support Date: 2013-07-29
Source: Cisco - Cisco PIX 500 Series Security Appliances - Retirement Notification
Cisco Community - PIX 515 Memory Question
Cisco - Configuring the PIX Firewall and VPN Clients Using PPTP, MPPE and IPSec
By clabretro on YouTube:
YouTube - THE UNTOLD STORY: How the PIX Firewall and NAT Saved the Internet on 2023-06-03 by The Serial Port.