The Digital Age

Hi everyone, it seems this is the most populated forum for CCTV to get some answers. I'm doing research on the conversion from Analogue to Digital and the effect it's had on everyday living. One of the most common conversions has been in surveillance.

My first question is, around which period would you say that DVR's started to out sell the old VCR system?

Also a big part of the research was the fact that a DVR could handle recording at high frame rates 20 fps or above and store them with ease whereas using the VCR it would usually be in time lapse mode and the frame rates would be as low as 1 fps. However just when I thought I had it clear I seen that a certain VHS recorder could record 40 hours real time (around 20fps) on a 160 minute tape. I thought that most you could record in real time on a VHS was around 8hours with a 4hr tape on EP.

So how was the above possible?

Thanks for any help on both questions.