Does MPEG4 mean longer rec. time with same disk size?

[Foxbat]

But all the BB adds for the HD-Tivo for $699 are touting a "120 GB drive". I know the original had 250GB, so this was my point.

As far as minimum drive size: I just went through the selection of new servers at work, and you can't get SCSI drives smaller than 36 GB anymore. By the time Windows 2020 Server requires that much disk space, the server itself will be obsolete...