The OS (short for Operating System) has a great deal to do with this. Microsoft OSes (read "Windows") and Apple OSes (read "Mac OS X or OS 9x) are very very different. For example, Macs don't read .exe which means that programs that work on Windows won't work on Macs (unless you have VPC, but this consumes too much CPU and RAM, plus it can't run everything).

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

"Raise your can of Beer on high
And seal your fate forever
Our best years have passed us by
The Golden Age Of Leather"
-Blue Öyster Cult-