Maximum PC: A few months after it started shipping the Scorpio Blue 7mm hard drive, aimed at Intel-based ultrabooks and other ultra-thin and light notebooks, Western Digital on Monday up the ante by announcing what it claims is the “world's thinnest 2.5-inch hybrid hard drive.” The world’s largest HDD maker said it has begun sampling the 5mm-thin hybrid HDD and will be showcasing the technology during the upcoming WD Investor Day on September 13, 2012.