Hello,
I have Sandisk 4gb usb. When i connect this to my pc- it shows that i have 3.72GB.
When i connect it to the Wii U, it shows that i have only 3.42GB.
Why is that?
Go check this, dude.
That is normal. It would never show up as 4GB on any other device wether a WII, a laptop or a PC. 4GB is being ready by the hardware. the one read on the operating system would be less because they read the drive differently. 
