Here's a lesson in actual vs. theoretical. Sony Optiarc America has announced the new BDX-S500U external USB 2.0 Blu-ray drive capable of burning single-layer BD-R discs at smoking speeds of 6x or dual-layer discs at up to 4x. If you do the math, those specs imply transfer speeds of 27Mbps for single-sided 25GB discs and total burn times of roughly 20 minutes. That's great news for folks with PCs looking to use the high-storage medium or watch 3D Blu-rays -- except for one tiny hitch. See, USB 2.0's theoretical maximum transfer speed is 60MBps, but in the real world most are lucky to get even half that rate. According to tests by
