Though the OP says BIOS password, laptops often have a bunch of different passwords that can be set:
the "actual" BIOS password. In older systems this is stored in CMOS RAM, kept "alive" by a battery. More recently, this data is stored in a flash chip, rather than volatile RAM, for which there is no way to clear it (by design).
Laptops often also have Hard drive passwords, which are part of the ATA standard. There are ways to "clear" a hard drive password, but they aren't pretty. Essentially the Hard drive requires the correct password before it even let's the computer do anything beyond a basic identification.
In additional oddness (and this is evidently purely anecdotal, but nonetheless) my older 755CDV had three batteries (the main battery, a standby battery, and the CMOS battery) But from what I could tell, the BIOS password that was set was not stored in the memory maintained by any of the batteries, since I removed them while trying to resolve other issues (specifically, it was having this weird confusing issue, system board failure, I think), but starting it up afterwards, it still prompted for and accepted the same BIOS password; and that was a laptop from ~1995.
