Sorry, I thought you had a fair idea as to what a PVR was
TiVo without a sub is set to record just like a VCR, ie set start & stop times and select channel. You can still do chase play (start watching before recording has finished) or watch a previous recording while recording another program. It does not however give you the EPG (Electronic Program Guide - TV listings to you & me
).
With the sub you get the EPG that gives all the info needed to use the season pass (record all episodes of a program), set wish lists to record everything by a set 'actor', 'director' or 'key word'. It can also auto record programs similar to those you have set to record, and you can give programs up to 3 thumbs up or down to rate them to give TiVo a helping hand on what sort of things you like. Auto record a repeat of a program if it was unable to record the origional showing due to recording something else at the time.
Oh there are so many things TiVo does that I just take for granted and always forget to mention when asked, and thats without the upgrades and hacks available. I'm sure Cyril or Blindlemon etc will add to the list at some point.
Mark.