Where to specify starting blank size when milling

[petee]

I'm posting this here as I'm assuming this part of the machine setup gets done in software and has nothing to do with the machine hardware. The hardware just goes where its told to by the Gcode.

Where and how do you specify to the machine what size the solid, be it metal,wood,plastic, is so the machine tool can approach the solid quickly and then slow up to commence machining?

I've browsed all kinds of threads trying to find the answer but being new to CNC I don't know the correct terminology for that part of the operation.

Also for an operation that has say two milling processes, a roughing one followed by a fine pass, where do you specify to the system how much material to leave on the rough pass and then pause for a tool change?

Even just a rough pointer will be a help so I can go away again and read up.

The software I'm studying the tutorials on at the moment is Mach3.