dan@Apple.COM (Dan Allen) (05/23/88)
The Mac provides OS support for globals being referenced off of register A5, but does NOT require or have any explicit support for DAs using register A4 for their globals. It just so happens that many development systems use A4 for DA globals. Sad but True Historical Note: once upon a time, desk accessories were going to get full MPW support for their own A5 world, with the driver runtime support libraries automatically switching A5. This pioneering work was done by Steve Hartwell, who helped port the original AT&T C libraries over for MPW. Unfortunately, his work was not able to be fully tested for MPW 1.0, so it was posponed. Then Steve left to go to work for Apple in France, and the code died a slow and quiet death. It turns out that earlier versions of the Finder created major problems with his strategy, and we were unable to quickly determine how many things would break. I think that the advent of MultiFinder caused people to forget about a A5 world for desk accessories, which is too bad. The scheme really worked quite well and perhaps someday it will find interest again. I think also that a clever desk accessory or even XCMD writer could implement this A5 switching stuff himself. Dan Allen Software Explorer Apple Computer