IP and Mac address: Why does a computer need two IDs

[theKbStockpiler]

I know this is described by layers but only one layer is actually on the net the others stay on the computer.

Thanks in advance!

[rcgreen]

Computers that are directly connected to each other
use the MAC address. This is at a lower layer than the IP address.
In fact, when you communicate between two computers on a
home network, say you ping one machine from another by IP
address, it first uses the ARP protocol to translate the
IP address to the MAC address.

The MAC address is physical, less abstract. It is how one network
card talks to another network card. The IP address is abstract,
and above that, even more abstract is a human readable name
like a host name or domain name.

The reason for the different levels of abstraction is so that
you could completely change the hardware (your network card)
into a totally different device (like fiber) and your software
(like the web browser) would still work.
Or you could change the IP addressing scheme (like IPv6)
and your hardware would not automatically become obsolete.