IBM PC/PCjr BASIC Compatibility
I would like to know if a program written for the PCjr in Cartridge BASIC would work on the PC with a color/graphics adapter and BASICA.
PCjr Cartridge BASIC is a superset of BASICA, which means that it contains all the commands found in BASICA plus some new ones. Likewise, the PCjr has all the graphics and sound features found in an IBM PC equipped with the color/graphics adapter, plus some enhancements. Therefore, programs written for a PCjr with Cartridge BASIC will run on a PC with a color/graphics adapter and BASICA only if the extra commands and features are not used.
An example of a new Cartridge BASIC command is PCOPY. Briefly, this command copies an image from one screen page to another. But only the PCjr with Cartridge BASIC has this capability. If you attempt to run the program on a PC, BASICA won't know how to interpret PCOPY and an error will result.
An example of an enhanced feature on the PCjr is SCREEN 5, a graphics mode with 320 × 200-pixel resolution and 16 simultaneous colors. A program written for the PCjr using SCREEN 5 won't run on a PC equipped with the color/graphics adapter, because the PC's 320 × 200 graphics mode (SCREEN 1) is capable of displaying only four simultaneous colors.
If you want to write programs on a PCjr with Cartridge BASIC that will be compatible with a PC and BASICA, you'll have to avoid using all of these new commands and features. For your guidance, IBM's Cartridge BASIC manual generally states when a command is available only in Cartridge BASIC. It would also help to acquire a BASICA manual and familiarize yourself with a PC outfitted with the IBM color/graphics adapter.