On Thu, 29 Oct 1998, Sam Ismail wrote:
As far as I know it was in the ROM on the motherboard.
If you turn the machine on with no disk in the drive and no cartridge in
either slot, you get ROM BASIC.
There is also a more advanced BASIC on a cartridge. If you turn the
machine on with the BASIC cartridge in a slot, you get cartridge BASIC.
This is not a guess. This is how my PCjr behaves.