a few questions on a 3-year old iMac. Owner is a Windoze person and doesn't understand Macs, thus can't understand specs. I'm retired and do no gaming. a) Whats the difference between a Dual Core or 2 Dual Core processor? Does it matter much? Is this speed related only? b) On my own, can I swap drives? And are they ATA or SATA? c) Link to ext HD for backup? Firewire 800, 400 or SATA? d) Can additional memory be installed by owner? e) Do iMacs have a fan for cooling? f) Are there spare slots (PC, PCI or whatever) ?