To answer that, would need to know WHICH PVR model you have. And then which size drive is in it.
The older units (8300), and the NB2s (8642) could have varying size of drives in them.
The NB3, only has a 1g drive.
I believe there is a sticker on the back/bottom, which says the size.
The 1gb drive on the NB3, is 'supposed to' be able to record of up to 240 hours of HD.
So depending on your drive size.. a 500g drive should be roughly max 120h, etc.
Rogers Ignite Xi6, LG 47LV5400 LED TV, Yamaha