You could try the following code to read the first K of the disk or sdcard.
File diskRoot = new File ("\\\\.\\PhysicalDrive0");
RandomAccessFile diskAccess = new RandomAccessFile (diskRoot, "r");
byte[] content = new byte[1024];
diskAccess.readFully (content);
Don't forget PhysicalDrive0 needs to be changed, On windows it would be 'C' or 'D' and you will require admin privs. On Android try 'sdcard0' and some phones 'extSDCard'.
I've not tried it, so let me know if it works.
/Darren