What causes software to be "incompatible?"

Hey, guys -- quick question.
What makes a software incompatible with a system?
I'm quite fond of Zonealarm, and I was really disappointed when
I found out that it caused my SZ to crash on every startup (something
about page faults). I don't think it's too memory taxing, since both
my desktop (Dimension 8300) and SZ have 1GB. Could it be processor speed?
1.83 Core Duo v. 2.80 Pentium IV?

P.S. Why is my Bus speed only 166 MHz?

Thanks for the help ^_^

 

Most likely it is other programs loading at the same time. You might shift the order that it appears in startup or in the registry and make it work.

'Cos that's what the Core Duo runs at. Intel uses some "Quad-Pumped" marketing hype to say the FSB is 667 (166*4=667) so their processors seem faster.

 

What you call incompatabilty happens when driver and dll's are not compatable. You by chance don't have another AV installed do you? I have seen this if a pc was infected with virus too. As well as different mfg of av. Generally when this happens boot into safe mode, do a uninstall, reboot. These programs (av and fw) do like programs running in back ground when doing installs. So to a right click on the icons located in the sytem try (bottom right), and shut down all that you can. The do a ctl+alt+del and see if any applications are running, close down all. The try the installation agian.