for Virgin Media's next generation set top boxes. Virgin Media will be the exclusive distributor of TiVo services and technology in the United Kingdom. Virgin Media released its first TiVo co-branded product in December 2010. On 17 March 2011, Virgin Media enabled access to a third tuner. As of 12 February 2015, Virgin Media has 2 million TiVo customers, 50% of their TV customers. Hardware anatomy The TiVo DVR was designed by TiVo Inc., which currently provides the hardware design and Linux-based TiVo software, and operates a subscription service (without which most models of TiVo will not operate). TiVo units have been manufactured by various OEMs, including Philips, Sony, Cisco, Hughes, Pioneer, Toshiba, and Humax, which license the software from TiVo Inc. To date, there have been six "series" of TiVo units produced. TiVo DVRs are based on PowerPC (Series1) or MIPS (Series2) processors connected to MPEG-2 encoder/decoder chips and high-capacity IDE/ATA hard drives. Series1 TiVo units used one or two drives of 13–60 GB; Series2 units have drives of 40–250 GB in size. TiVo has also partnered with Western Digital to create an external hard drive, the My DVR Expander, for TiVo HD and Series3 Boxes. It plugs into the TiVo box using an eSATA interface. It expands the High-Definition boxes by up to 67 hours of HD, and around 300 hours of standard programming. Other TiVo users have found many ways to expand TiVo storage, although these methods are not supported by TiVo, and may void the warranty. Some recent models manufactured by Toshiba, Pioneer, and Humax, under license from TiVo, contain DVD-R/RW drives. The models can transfer recordings from the built-in hard drive to DVD Video compliant disc, playable in most modern DVD systems. All standalone TiVo DVRs have coax/RF-in and an internal cable-ready tuner, as well as analog video input — composite/RCA and S-Video, for use with an external cable box or satellite receiver. The TiVo unit can use a serial cable or infrared blasters to control the external receiver. They have coax/RF, composite/RCA, and S-Video output, and the DVD systems also have component out. Audio is RCA stereo, and the DVD systems also have digital optical out. Until 2006, standalone TiVo systems could only record one channel at a time, though a dual-tuner Series2DT (S2DT) box was introduced in April 2006. The S2DT has two internal cable-ready tuners and it supports a single external cable