This modification will allow you to have two DOSs in a CPC6128 without the need of an addition additional PCB. By replacing the standard 16K EPROM with a 32K and switching the MSB (A14), you can choose the DOS that the CPC uses.
If you don't like making changes inside your CPC, then check out the [[LowerROM|LowerROM Board]] external solution.
== Warning / Disclaimer ==
Next you need to solder a flylead to pin 14 and pin 27. These leads need to go to a standard normally open switch mounted on the CPCs casing.
Closing the switch will set A14 to 0 zero and opening it sets A14 to one. This allows you to enable the upper or lower 16K of the EPROM and thus select which OS the CPC sees.
The EPROM should be burnt with whatever two OSs you wish to have, the first OS is saved from &0000 to &3FFF and the second OS should be located from at &4000 to &7FFF.
The ROM image below is a single 32K file with AMSDOS and ParaDOS.