By late 1995 or early 1996, Apple expects to ship Power Macs that use the PowerPC 604 chip. This supposedly will be the leader of the 32-bit pack, but not much else has been revealed. The final PowerPC chip announced for Apple computers (so far) is the 620, a completely 64-bit design due sometime in 1996. All we have been told is that the 620 will offer super-fast multiprocessing for big-time workstations and supercomputers. By the way, Motorola also is developing market-specific PowerPC chips for consumer electronics, computer peripherals, and assorted control and communications applications.

One minor drag is that System 7 still uses cooperative multitasking instead of the preemptive multitasking offered in the Commodore Amiga. This means that although applications can run in the background, there will still be times when one operation takes over your Mac, and you have to wait to switch programs. Apple apparently is considering changing to preemptive multitasking someday-it's an operating system issue, not a hardware limitation-but it is a low priority at the moment. Besides, it could open a can of worms for developers.

Dancing Madly Backward
Fast hardware notwithstanding, many potential Power Mac customers will remain on the fence until two issues are resolved. First, Apple's claims of excellent backward compatibility (i.e., emulation of the 680x0 instruction set) must be confirmed in real-world use. Next, programs must be written specifically for the Power Mac to achieve the smoking-fast performance Apple promises.

A certain amount of compatibility problems are inevitable when a major hardware or operating system changes: many Macintosh users had problems switching to System 7, the 68040 CPUs, and the PowerBooks. PC folks had to go through hard times with Windows, despite Intel's and Microsoft's attention to compatibility issues. And don't even ask an Atari ST user about the problems encountered when upgrading to the Mega. Apple warns us to expect problems with as much as ten percent of existing programs, which is pretty good.

Apple's confidence in the Power Mac's backward compatibility is rooted in the fact that the new computers have the 68LC040 instruction set stored in ROM. To a pre-Power Mac program, a Power Mac looks a 68040. A Mix Mode Manager lets 680x0 code and PowerPC code run at the same time.

Also, the Power Macs operate under System 7.1.2, which is call-for-call compatible with System 7.1. In theory, anything that is 68040-compatible and System 7.1-compatible should run fine.