Western Digital may have been quick to release a 5mm hard drive, but it doesn't have a lock on the category: Seagate is entering the fray by shipping its own slim disk, the Laptop Ultrathin. Like its rival, the drive stuffs as much as 500GB of conventional, rotating storage into SSD-like dimensions ideal for Ultrabooks and some tablets. It even costs the same $89 as its WD counterpart, although we're more likely to find the disk built into our n
