TiVo drives use a "modified Apple partition map." It appears to me that only the volume header block (block zero) is modified from what Apple uses for their APM (Apple Partition Map) format. The rest of the partition map seems indistinguishable from a standard APM format disk. So, I'm trying to figure out block zero. Here's what I have been able to figure out about block 0 on TiVo drives: TiVo volume header, one block of 512 bytes. Bytes 0-1: ("14 92") Unknown. On APM volumes, these bytes are the signature "ER" so perhaps the bytes "14 92" are a TiVo signature. These bytes are the same on all the drives I've checked so far. Bytes 2-3: "03 06" or "06 03" indicating the boot partition, either 4 or 7 (zero-based). Byte 4 starts the string: "root=/dev/hda7" or "root=/dev/hda4" which is null terminated. This string matches the order indicated by bytes 2-3. Byte 19 starts the string: "runfactorydiag=true dsscon=true brev=0x1031" and is null terminated. I've seen other strings including: "runfinaltest=2 brev=0x10 contigmem8=16M=16M" and partially overwritten strings like: "unfinaltest=tru" so I'm not convinced these bytes are all that important. Bytes 63 through 131, all nulls Byte 132 starts the string: "unnamed" and is null terminated. This seems to be the same on every drive I've checked. Bytes 140 through 163, all nulls. Bytes 164 through 174 unknown, These vary from one drive to another. 40 GB drive: 0A 54 8F 49 B2 32 31 60 75 92 3C 60 GB drive: 0A E8 E1 80 8F 9D 03 B0 0B E8 3C 80 GB drive: 0A 8D 2F 4C D2 3D 9C 58 7B 16 3C another 80 GB drive: 0A 6E 00 85 01 7A DC 72 7E 4D 3C As shown above, byte 164 is always "0A" and byte 174 is always "3C" on each drive I've checked. I have no idea what these bytes indicate. Bytes 175 through 511, all nulls. If any of you can identify the purpose of bytes 0-1 and/or bytes 164-174, please enlighten me. FYI, the reason I'm interested in this is that I have, on multiple occasions, lost all my recordings when a TiVo became unbootable. Subsequent efforts to rescue data using Linux-based tools gave the error that the volume header was corrupted. Hence, I want to know more about the volume header so that I can effect repairs, should I ever have another corrupted volume header.