box or satellite receiver. The S2DT is therefore capable of recording two analog cable channels, one analog and one digital cable channel, or one analog cable and one satellite channel at a time, with the correct programming sources. Note, however, that the S2DT, unlike earlier units, cannot record from an antenna. This is due to an FCC mandate that all devices sold after March 2007 with an NTSC tuner must also contain an ATSC tuner. TiVo therefore had to choose between adding ATSC support, or removing NTSC support. With the S2DT they opted to remove NTSC; the Series3 supports NTSC and ATSC, along with digital cable channels (with CableCards). The Series2 DVRs also have USB ports, currently used only to support network (wired Ethernet and WiFi) adapters. The early Series2 units, models starting with 110/130/140, have USB1.1 hardware, while all other systems have USB2.0. There have been four major generations of Series2 units. The TiVo-branded 1xx and 2xx generations were solid grey-black. The main difference was the upgrade from USB 1.1 to the much faster USB 2.0. The 5xx generation was a new design. The chassis is silver with a white oval in the faceplate. The white oval is backlit, leading to these units being called "Nightlight" boxes. The 5xx generation was designed to reduce costs, and this also caused a noticeable drop in performance in the system menus as well as a large performance drop in network transfers. The 5xx generation also introduced changes in the boot PROM that make them unmodifiable without extensive wiring changes. The 6xx generation resembles the previous 5xx model, except that it has a black oval. The 6xx is a new design and the only model available today is the S2DT with dual tuners and a built-in 10/100baseT Ethernet port as well. The 6xx is the best performing Series2 to date, outperforming even the old leader, the 2xx, and far better than the lowest performing 5xx. Some TiVo systems are integrated with DirecTV receivers. These "DirecTiVo" recorders record the incoming satellite MPEG-2 digital stream directly to hard disk without conversion. Because of this and the fact that they have two tuners, DirecTiVos are able to record two programs at once. In addition, the lack of digital conversion allows recorded video to be of the same quality as live video. DirecTiVos have no MPEG encoder chip, and can only record DirecTV streams. However, DirecTV has