Battery Life Matters
Let’s talk about battery life. There are a lot of things that can make battery life better. Intel claims that their innovation and fruitful partner collaboration will help increase it over time. In the past Intel talked a lot about SpeedStep technology that steps down frequency and voltage. They also introduced power management technology.
This year in Santa Rosa they brought back power management capabilities. In particular they announced that they did a lot of managing with partners from Toshiba and Matsushita Technologies to control the display power. Also, a lot of effort was invested into managing the CPU and graphics power, so that the power could be balanced between these two subsystems depending on the workload at a given moment of time. They claim they have 6 other new technologies that will be brought into Montevina.
They introduced the Deep Power Down State that is taking the idle core of the running processor to 0.
They tried to balance efficiently between voltage reduction and exit/enter latencies. The main constraint in this case was data retention, because they had to make sure that the data is retained when the voltage is lowered. How doe it work? The processor content is saved into on-die memory which is always powered on. And since this operation can be performed very quickly, Intel engineers got the ability to play with the voltage and power as they wished until they found the most optimal ratio.
There is also very tight communication between the mobile chipset and CPU. The chipset protects the CPU from waking up, because wake-ups consume a lot of power. To avoid numerous wake-ups the chipset stores some frequently requested info and retains the knowledge of what is going on. Sometime user interrupt requires the CPU to wake up and perform a few instructions. In case the frequency and power can be balanced so that the CPU reassigns these instructions to the powered core, the net power saving is tremendous.
Here is what it looks like in action:
As you see from the pictures above, in Penryn Intel takes it one step forward: they take the cache power off completely and reduce the core voltage way down.
In Nehalem they promise to go even beyond that thus increasing the battery life and driving the power savings down even more.