HDD 2.5" ATA100 to ATA66

[zelimir]

Can I install a new ATA100 HDD instead of an old ATA66 disk. Laptop is
Siemens_Fujitsu E-series. Old HDD was Toshiba MK2016GAP. I am not expecting ATA100 features, of course, but I am worry about connector,voltages, Bios e.t.c. What about diff. manufacturer?

[soybean]

That should work fine.  diff. manufacturer is not an issue.  connector,voltages would be the same; no difference there between ATA100 and ATA66.

As you said, if the computer is an ATA66 machine, it simply won't be able to take full advantage of the ATA100 speed.