When you're designing an external optical drive, you need to keep a couple of things in mind. Being external, it needs to be relatively small; people buy external drives for portability, after all. It also needs to be reasonably robust; unlike an internal drive, an external drive is likely to undergo more knocks than average. Sony's slim DRX-S70U drive addresses both of these areas neatly. It's a slim (135.5x19x154mm) and light (440g) drive in a rigid black metal casing. As such, it should slip into most notebook bags without creating too much of a bulge -- if it weren't for the AC power adaptor and USB 2.0 cable, which expand its bag size noticeably.
The DRX-S70U is a combo DVD/CD burner with support for every format you'd care to throw into it, from humble CD to DVD+R DL. Rated write speeds are 8x (DVD+/-R), 8x (DVD+RW), 6x (DVD-RW) 4x (DVD+/- R DL) and 24x (CD/CD-RW).
The DRX-S70U requires AC power to operate and a 5.2V AC adaptor is provided, along with a short length of USB cable. On the software side, Sony provides Nero 7 Essentials for Windows. That gives you the very cut down Nero 7 suite, substituting Nero Express for Nero Burning ROM, and the lower specification "essentials" versions of Nero Vision, Showtime and MediaHome. The notes on the drive declare it to be Mac compatible, although no Mac software is provided with the drive itself.
The drive within the DRX-S70U was revealed to be an Optiarc AD7540A drive -- Optiarc is a joint venture between Sony and NEC -- and basic testing revealed it to run at at an average of 5.3x on a 4.7GB DVD-R disc, a touch lower than the stated 8x that Sony states it's capable of. DVD discs created with the DRX-S70U took around twelve minutes to complete in our tests.