We were intrigued with the prospects of Western Digital's 5mm Blue drive when we saw it last summer: finally, a 2.5-inch spinning disk thin enough to rival slimmer SSDs without the price premium of a hybrid like the WD Black SSHD. If you shared the same curiosity, you'll be glad to hear that the finished product is shipping as the WD Blue UltraSlim. Device builders can now stuff 500GB into spaces that would exclude 7mm disks, yet pay just $89 for the privilege -- a price low enough to let even frugal Ultrabooks shed some bulk. The 5mm disk reaches its miniscule dimensions through the use of a tiny edge connector that mates both power and a SATA interface, leaving more room for the drive machinery. We can't guarantee that you'll find a Blue UltraSlim in your next PC or set-top box when Western Digital hasn't named any of its customers, but we wouldn't be surprised if the wafer-like drive is commonplace in the near future.