If you have booted from SRM and you select this option, the installer will write aboot to the first sector of the disk on which you installed Debian. Be very careful — it is not possible to boot multiple operating systems (e.g. GNU/Linux, Free/Open/NetBSD, OSF/1 a.k.a. Digital Unix a.k.a. Tru64 Unix, or OpenVMS) from the same disk. If you also have a different operating system installed on the disk where you have installed Debian, you will have to boot GNU/Linux from a floppy instead.