TiVo Hard Drives
The hard drive is the basic storage item on any DVR. On a TiVo, it contains four primary different types of information: the OS, user settings, guide data, and programming. The last of these, programming, takes up the vast majority of the space on the drive.
TiVo has always used a special type of hard drives made specifically for DVRs. The drives in the first TiVos were all Quantum drives from their QuickView line - the first special sub-brand of drives made with tweaks for DVR use. Quantum was later bought by Maxtor, who used the QuickView branding on their own drives that they then adjusted to perform better in DVRs. Maxtor, in turn, was absorbed by Seagate even later. Seagate had already been producing a line of drives for DVRs called DB35 (similar in name and concept to their SV35 line of drives for security and surveillance cameras). Seagate then discontinued production of the Maxtor QuickView drives.
Western Digital has had several different lines of DVR-specific drives. Originally they produced drives from the Entertainer series. Those first went in Series2 TiVos at the 60 GB size. Later, Western Digital changed the name to Performer. Still later, they dropped the naming altogether and only distinguished the DVR drives from regular drives by appending a "-55" to the full model number of these drives. In the SATA world, WD has been using a different model number series to distinguish the DVR-tuned drives: EVCS.
IBM drives never were really used in the DVR world until after their purchase by Hitachi. As Hitachi became the leader in large capacity drives for a time, they marketed a SATA line of drives called CinemaStar which were also tuned for DVRs and perform well.
The other major drive contender in the market has been Samsung. Samsung has generally been at the lowest end of the price spectrum, and therefore has been a compelling choice for that reason alone for many companies. But their drives never performed well in DVRs, and, surprisingly, even for the DVRs that they manufactured for DirecTV, they actually used Western Digital hard drives exclusively.
Until the introduction of the Series3 TiVo, all TiVo DVRs used internal IDE drives. The Series3 and TiVo HD are the first units to use the newer SATA formatted drives. In these models, TiVo is using Western Digital drives.
The Series3 and TiVo HD also marked the first way to use external drives for extra recording capacity. Both units have eSATA ports, and can accept an external drive that is made by Western Digital called the My DVR Expander. This drive is only available in one size: 500 GB. The Series3 units can also accept other external hard drives, up to 1 Terabyte in size.
TiVo Hard Drive Failure
Since the hard drive is the primary moving part inside a TiVo, it's the part most likely to fail over time. Even with the special firmware and tweaks on DVR hard drives, most drives don't last longer than four years due to the contant, 24/7 reading and writing. These drives are always buffering live TV and are therefore used much, much more heavily than standard computer hard drives.
The failure of TiVo hard drives has spawned an entire industry of hard drive replacement vendors. In most cases, the replacement hard drives need to be specially formatted for each type of unit, and vendors generally use the same DVR lines of drives from hard drive manufacturers.
TiVo Drive Upgrades
As mentioned above, a series of companies have created a niche for themselves by offering formatted replacement for failed TiVo hard drives. In addition, they are able to offer larger and secondary drives for TiVo DVRs to increase overall recording capacity, in many cases to thousands of hours of storage.
The most prominent and largest TiVo upgrade company is Weaknees. They have upgrades for every model of TiVo, currently.
Other companies exist including TVRevo TiVo Upgrades and Hinsdale/New Releases Video. Also, for do-it-yourself upgraders, online TiVo upgrade instructions are available.
DVRupgrade, the first TiVo upgrade company, also sells many related parts.