This item is from the Yet Another Enhanced IDE/Fast-ATA/ATA-2 FAQ, by John Wehman and Peter den Haan with numerous contributions by others. (v1.92).
Transferring a partitioned and formatted harddisk between computers is potentially dangerous if they use different translation schemes (see Q 6.3). This includes moving a disk from an old computer that doesn't support translation to a new one that does. This is really a little known issue. Usually everything goes smoothly, but you would not be the first to be caught by surprise.
WARNING. Do not assume it won't happen to you just because it works out fine most of the time---it has destroyed data, and will do so again.