Vimm hosts these downloads on hard drives and solid state drives. He's doing some maintenance with the PS2 drives, so they'll be down for however long he needs.
As to how a game is transferred from a disc to a computer file, I don't actually know myself, I would assume that with DVDs and other disc based media, they're placed into a suitable disc player and ripped with some form of programme. Might wanna do some searching or asking on a forum dedicated to this stuff if you want a good answer.
"NintenDON'T sue me please haha"
So I was wanting to play FFX but it didn't download, all it said was "PS2 downloads are offline today while a disk is moved." So does that mean the emulation team is working on fixing or adjusting something? I'm just curious. Also, can someone explain to me how a game is transferred from a disc to a computer file?