Since you may be looking for more Analysis of Apple’s A4 custom applications processor after reading a recent EE Times article, I thought I would provide a bit more of the thinking that was done in preparation for that. If you landed here randomly or just check this blog regularly (okay, so I know you both personally, and I could just pick up the phone), you might want to have a look at that article. Or you can check back to the publications page for a high resolution die photo coming soon. Or you could just skip this introductory nonsense and get on with reading this post.
I think some fellow bloggers joined Young Choi over at UBM in saying that differences in power consumption between apps processors are a drop in the bucket compared to what the display - especially the big one on the iPad - consumes. Young did a a very useful review of the trends in apps procs from the full line of Apple mobile devices. He ends his own EE Times article with a thought that is quite true:
“Until display technologies make big moves downward in power consumption the consumer experience of battery life may be driven as much or more by the LED drivers, opto-mechanical design of the back-lighting, display settings and wireless connectivity employed versus the CPU itself.”
Certainly, there is no avoiding burning a lot of battery power to light up the display, but it’s still interesting to think through the differences between pre-A4 platforms, and the two we know for sure have sockets for it.
Apple specifications claim similar device life for web surfing over WiFi - 10 hours for iPad and nine hours for iPhone 3GS. Factoring in the 10 percent lower life, a screen area increase for lighting of eight times the iPhone's 3.5 inch diagonal, and the six times bigger battery in the iPad, the chips in play for the surfing task are providing nearly 50% longer battery life. It's an oversimplification, but one could assume (especially if you are Apple PR) that much of the improvement comes from the A4 design compared to the processor used in the iPhone 3GS. Architecturally at least, there is no evidence that this big power saving would come from throwing away unnecessary circuit blocks from a generic off-the-shelf standard product. A few bloggers thought that the A4 would not support camera functionality since the iPad didn't, but I doubt you needed to wait for the the June 7 Keynote and the iPhone 4 announcement to realize that at least one A4 product platform would contain a camera.
With the iPhone 4 announcement at WWDC 2010 and official Apple specs now available, a better A4 to 3GS processor comparison is possible. Unfortunately for the custom chip side, this doesn't do much for the A4’s reputation as an energy miser. Apple's iPhone 4 video describes a much bigger battery than the 3GS that offers "up to 40% more talk time." However, the web surfing life connected by WiFi is listed at 10 hours for iPhone 4 versus nine for the 3GS. That leaves little room to conclude that the new A4 design or its 45nm Samsung process technology offer any power savings as it is configured for the iPhone. That is unless Apple has channeled the power saving into brightening its new Retina Display. Although the physical area is the same, the iPhone 4 team may have decided to increase the visual impact of the new screen by increasing the power supplied to its LED backlight. Once legally available versions of iPhone 4 are available, we will know for sure.
