conditional hard drives

[Albert Vilella]

Hi all,

I have a laptop with an internal hard drive (sda) where I have a linux
and a windows that I can pick to boot up with grub.

I also installed a different linux on this laptop but using an
external usb hard drive (sdb).

Now grub will work fine when the sdb hard drive is plugged in one of
the usb sockets, but will fail if it is not.

Is there a way to make the extra boot options conditional, so that I
can boot up the main linux and windows without having the sdb plugged
in?

Thanks in advance,

   Albert.