Apple Computer Inc’s new Powerbook laptop machines will be upgradable to a PowerPC processor – but just which PowerPC appears to be in some doubt. Apple has always said that the PowerBooks and low-end desktop machines would use the low-Wattage PowerPC processor. However references to this have now disappeared and the current issue of MacWeek […]
Apple Computer Inc’s new Powerbook laptop machines will be upgradable to a PowerPC processor – but just which PowerPC appears to be in some doubt. Apple has always said that the PowerBooks and low-end desktop machines would use the low-Wattage PowerPC processor. However references to this have now disappeared and the current issue of MacWeek reports that the company has given up on the current 603 because of problems running the 68000 emulator, and is pushing for a new chip, the 603+. There are six new models of PowerBook. The four high-end 500-series machines are the ones that are upgradable. They do away with the old track-ball and replace it with a touch-sensitive membrane – odd, at first, though the company says you get used to it after a couple of hours. They also feature built-in Ethernet, optional PCMCIA expansion and ‘intelligent batteries’ to aid power management. The chassis also features a Processor Direct slot to take an upgrade processor board. The two 200-series machines are characterised as subnotebooks, and lack the upgrade capabilities. Apple is being curiously reticent about what form the upgrade will take, saying that the MacWeek article is speculative and adding that the company is still evaluating the 603. Still MacWeek reports that sources are adamant that Apple has eliminated the existing 603 chip from its development. The problem is the size of 603’s on-chip cache, which is only half of the PowerPC 601 cache. The emulation approach Apple has chosen is highly reliant on cache size; in essence it has implemented a large look-up table where each 68000 instruction is mapped to a particular RISC-instruction routine. The bigger the chip’s primary cache, the more emulator can fit in it, and the faster it goes. One curious aspect of the story is why Apple should only be evaluating the PowerPC 603 when it is supposedly involved in designing the chips at the Somerset design facility. One reason may be that it was hoping that some newly designed 68000 emulation software would improve the chip’s performance. Sources at AppleSoft have confirmed MacWeek’s reports of the new emulation software, but could give no details. Speculation on the Internet is that Apple may be experimenting with compilation on the fly emulation similar to IBM Corp’s instruction-set translator and Insignia Solution Ltd’s SoftWindows. But the US magazine reports that even this new approach managed to improve the performance only slightly and as a result, Apple wants a 603+ chip, with the higher clock-speed and larger cache.