== Technical ==
BOS ROM exists at rom slot 6 and is decoded exactly (no repeat).
DFxx is decoded by the Vortex RAM Expansion (for BOS) and uses xx0xxxxx xxxxxxxx xxxxxxxx xxxxxxxx (same as other ROM expansions).
The FBBD port is decoded as: xxxxx0xxx0xxxx0x
This means just 3 bits are decoded for it.
Data written to the vortex RAM doesn't write through to main RAM.
On Reset the BOS rom is activated.
== Description ==