I installed O.S. 7.5.3 onto an older 256mb Kingston CF card. It took a couple of tries to get it finished. It's boots up faster, and everything works about the same, maby a bit faster.

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Please do your comrades the favor and share your findings in the Wiki page Flash Drive Test Results. Especially exact information on the CF card type/vendor and driver software are useful to multiply your success
As far as I know the PB 1400 (as the PB 150, too) needs a CF card identifying as "fixed media" to (edit: cold-)boot* from the internal drive bay. Does the IDE-CF adaptor have any electronics on the PCB to set such mode or are you lucky to use an industrial CF card ?

*Once the machine has an appropriate driver in RAM, a restart using the CF card as boot disk will work. This works only if booted from another drive in the first place.