PIX515 interfaces, How many without having 4PORT card installed?

[yeo]

The PIX515 comes with 2 interfaces and can support up to 6 if you have the correct software installed. I am wondering if I can upgrade my 3 port PIX to a 4 port with the addition of a single 10/100 NIc from Cisco or do I have to trash the extra single port I have and buy the 4 port?

[gfullage]

Yes, you can install a 2nd PIX-1E into the extra slot. See http://www.cisco.com/univercd/cc/td/doc/product/iaabu/pix/pix_sw/v_62/hig/515.htm (it's hard to find, so I'll cut/paste):

If your unit has a four-port Ethernet circuit board already installed, refer to Figure 4-8. (The four-port Ethernet circuit board requires the PIX-515/515E-UR license to be accessed.) If it has one or two single-port Ethernet circuit boards, refer to Figure 4-9.