PVR Wire

Doug Felteau at DVR Playground has written an indispensable little article for anyone looking to upgrade or replace their TiVo hard drives.
If you're under the impression that you can pop the top off of your TiVo, remove the hard drive, copy some info over onto a new one, pop it back in and suddenly have 2 to 10 times the amount of storage you started with, you're only partially right.

For example, did you know that Series1 and Series2 TiVo units use ATA, UATA, and PATA drives while Series3 units use SATA? Did you know that a 5400 or 7200RPM hard drive will work just fine, while a drive with 4200RPM is too slow and a 10000RPM drive is a waste of money because your TiVo won't be able to keep up with that speed anyway?

A few other tips:

• Series1 TiVo units can only access 137GB of hard drive space, although if you throw 2 HDDs in there, you can double this to 274GB.
• Older Series2 units require software version 7.1 to use hard drives larger than 137GB, while newer Series2 units can make due with version 5.1 or higher. DirecTV Series2 units need version 6.1, while the DirecTV HD PVR can use larger hard drives with software version 3.1 or higher.
• Series3 units come with a 250GB hard drive, which you can expand with Western Digital or other SATA hard drives.
• For upgrading a Series1 or Series2 unit, most hard drive brands will do, although Felteau suggests that the Maxtor Quickview or Seagate DB35 tend to make the least noise.
  

Anyway, there's a lot more information and links to tutorials that will actually walk you through the upgrade over at DVR Playground. Or if you're too squeamish to hack your own TiVo, the folks at WeaKnees or DVR Upgrade would be more than happy to take your money and do it for you.