All three technologies, Analog, AHD and IP/Network Camera use cameras to record images onto a recording device. In an SD or analog system, this is a DVR (Digital Video Recorder) and in an IP system, it is an NVR (Network Video Recorder). AHD systems use a hybrid recorder. All these devices record, playback and store video footage (plus you can remotely view video).
In an analog or AHD CCTV system the signal is then converted to analog and sent to the DVR over copper wires (coax or UTP) where it is converted back to digital, compressed and recorded by the device. Conversion from digital to analog and then back to digital can create a loss in recorded image quality when comparing the output from the cameras image sensor to what is recorded on the DVR.
In an IP system, however, the camera itself compresses and encodes the digital signal and then sends it to the NVR via IP (Internet Protocol). The NVR then records or copies the actual video file from the camera. Because there is no conversion between digital and analog and back there is no loss in picture quality.
The storage capacity is concerned, different models of DVR,NVRs have different capacity and different number of SATA connections. Generally, we can use from 500GB to 6TB in each SATA connections. The duration of recording depends on the quality of the video in terms of resolutions and the capacity of the Hard Disk drive installed in that recording device.
