Hard drive 1 fast 303 is a system diagnostic error issued by HP System Diagnostics. This error usually occurs after an accident with an HP laptop or laptop computers, such as a fall on the floor or a severe shock. When you start the HP computer, it does not boot properly and redirects you to the diagnostic system. After running a self-test of the primary hard drive, you will see a “Hard drive fast 303” error. Sometimes you may also see a “Hard drive 1 full 305” error.