recording or playing back native progressive video. Because HDV 1080i specification now includes both interlaced and progressive recording modes, in recent publications it is often called HDV 1080 or 1080-line HDV, but the official name still bears the "i" suffix. HDV camcorders capable of native 1080-line progressive video record it at rates of 23.98 frame/s (commonly referred to as "24p") and 29.97 frame/s ("30p") for 60 Hz markets, and at 25 frame/s ("25p") for 50 Hz markets. Video is output as true progressive video via an i.LINK/FireWire port. Output through other ports is performed in interlaced mode to preserve compatibility with existing interlaced equipment. The first 1080-line HDV camcorder to offer recording in native progressive format was the Canon XL H1, introduced in 2006. It was followed by the XH-G1 and XH-A1. When shooting in progressive mode, also known as Frame mode, these camcorders generate progressive video from interlaced CCD sensors. Because of row-pair summation, vertical resolution of progressive video is 10–25% lower than resolution of interlaced video. In 2008 Sony released its own models capable of native progressive recording: the HVR-S270, the HVR-Z7 and the HVR-Z5. Sony stressed out that the models handle the signal entirely in progressive mode all the way from capture to encoding to recording on tape to output. Sony has designed Native Progressive Recording logo for the devices that are capable of native progressive recording and playback. In 2009 Canon released the HV40 HDV camcorder. Its 60 Hz variant, carrying prominent 24p native progressive mark, became the first consumer HDV model to offer 24-frame/s native progressive recording. Like the aforementioned Sony models, the HV40 uses true progressive-scan sensor. Despite differences in branding, native progressive modes offered by Canon and Sony are fully compatible, with both companies adhering to HDV specifications for recording native 1080p video. Other HDV devices capable of reading and recording in native progressive 1080-line format include the Sony HVR-M15AU, HVR-25AU, HVR-M15AE, HVR-25AE and HVR-M35 HDV videocassette recorders, and the 60 Hz Canon HV20/HV30 camcorders when used in tape recorder mode. Compatibility Generally, HDV devices are capable of playing and recording in DV format, though this is not required by HDV specification. Many HDV devices manufactured by Sony are capable of playing and recording in DVCAM format. 1080-line devices generally are not compatible with 720-line devices, though some standalone tape decks accept both HDV flavors. Devices that can play and record native 1080p