Answer:
4,294,967,296; theoretically
Step-by-step explanation:
There is 1024 bytes in a kb, 1024 kb in a mb, 1024 mb in a gb.
So we can use 1024³ as a multiplier to convert gb->byte.
1024³ * 4 = 4,294,967,296 bytes.
However, in practice hardrives always have less useable storage than the quoted amount.