ADAT?

I don't mean to be a wise a$s, but this is the type of info that you can find from google in a couple of seconds.. So in the time it takes for you to wait for someone to reply you could have already answered all of those questions yourself just by doing a little bit of work.
Now I don't mind helping people out, and I got no problem answering newbie questions either but it seems like everytime you run into a problem you just ask about it straight away, without even bothering to look it up in the manual or anywhere else. Most of the time all of the answers are easy to find by searching for it yourself...

ADAT used to be the industry standard digital multitrack... they got so cheap because now pro tools is the industry standard.

Now a days people use ADAT optical / lightpipe to multi-track. It is basically the ability to record 8 tracks simultaneously to your multitracking software just like you would to an ADAT recorder. Check out the Hammerfield website and the Behringer ADA8000 also the MOTU 828 all of these use lightpipe or ADAT optical technology.

Actually the behringer ADA8000 is only $200, but you have to get a soundcard that has ADAT optical inputs like the EMU cards or the ones afforementioned.