Gamejackel type mdfing?

hey guys
ok so my friend stumbled apon somthing really really wierd. he was looking around on the web and found this mdf\mds thing for the sims2. but the intersting thing is that it was only 1.56ish mb. so he sent me the file i loaded it up with alcohol 120% and ran the sims2 (which i own) and it ran perfectlY!? now how is it that this unknown person who made this mdf, can fit the sims2 into 1.56 mb while im stuck making 500-800 mb mdf\mds’s!??!?!
does anyone have any ideas?

o and if you guys need the file i could put that up on my ftp too if you need it

No warez here.

wait? how would this apply as warez? i just want to know how to make the mdf\mds file shrink down to 1.54 (i own the game i want to make my own mdfs\mds’s smaller)

It is a modified disc image and not allowed here.