The first partition (boot) must be less than 2GB
OS3.9 boots happily from a 6GB partition with FFS 45.1.
The only important rule is: if you boot from the internal IDE bus the boot partition has to reside entirely inside the first 4GB of the HDD.
If your boot partition is on another controller or you use a different file system, other rules apply. Check the docs of your hard- and software.
Bye,
Thomas
