There were a handful of pointers to the routines to use for BASIC execution in RAM starting at address $300, which could be pointed elsewhere for BASIC extenders or to redirect IRQs. Apart from that, most syscall addresses where in ROM.
It allowed disabling parts of the ROM though to access the full RAM. That way you could rewrite the real jump addresses, bypassing the ROM completely.
There were a handful of pointers to the routines to use for BASIC execution in RAM starting at address $300, which could be pointed elsewhere for BASIC extenders or to redirect IRQs. Apart from that, most syscall addresses where in ROM.
It allowed disabling parts of the ROM though to access the full RAM. That way you could rewrite the real jump addresses, bypassing the ROM completely.