Windows hard drive throughput for HD PVR

For a Windows HD PVR, is writing to/reading from the hard drive a bottleneck? I have seen file size numbers from 2 to 8 gigabyes per hour. 8GB per hour is 8192 / 3600 = 2.3 megabytes/sec. How close is that to 100% throughput capacity and where are the bottlenecks? Obviously this is dependant on what kind of hard drive you choose so a generic explanation is fine but specific examples would be great too.


TIA!