What is the maximum capacity of a hard disk

The current maximum is the largest per platter drive times 4. They just came out with 667GB per platter drives, so 667GB x 4platters = 2.67TB. I thought I heard 3TB drives were coming out soon so I'm probably missing something somewhere. As we get bigger and bigger platters, we get bigger and bigger drives.

As for the largest possible drives, I'm not sure. Are we using 48Bit access now? 2^48? Many 100s of TBs.

It also depends on your budget

How much do you wanna spend?  

Budget != maximum
GB/platter x # of platters = maximum

Budget only matters if he asked "whats the biggest drive I can buy with $XX.xx".

What'll he do by knowing which is the highest storage capacity of a HD???

Try to impress someone? I have no idea, I'm answering the question as it was asked for once.