Haswell and Power Savings (maybe?)

Intel’s next micro-architecture (‘Haswell’) has a new feature that can possibly result in a significant reduction in power consumption. They have added a power save mode that will essentially put the current view on the desktop to a static image that will be placed in a display’s DRAM. During which, the processor can go to sleep and consequently all the attached peripherals. Currently, your display is refreshed upto 60 times a second, and this is unnecessary in some situations. Say for example you are reading a lenghty document on a single page that is visible in it’s entirety on your display. Your CPU doesn’t really need to access to refresh your monitor 60 times a second, because the image is essentially static. Thus the CPU can remain off during that time, as long as the buffered screen is on the DRAM of your monitor.  This use case in my opinion is rarely encountered, people are likely to disturb the screen with their mouse and frequently toggle between screens. It can however be used for screensaver mode, where the system needs to update the pictures on the screensaver every few seconds. Here’s a nice demo.


Personally, I have a few concerns.

  1. How often are these usage scenario’s encountered in reality, where PSR (Panel Self Refresh) can be used.
  2. Will display manufacturers welcome this change? (They need to add the DRAM to their BOM, and how is the DRAM sized?)
  3. And does this feature really justify it’s purpose, I mean the display is in itself the largest source of power. Even if it is not being driven by the CPU as frequently, I’m thinking that since the back-light is still on. The power savings is minimal.

Still, beyond these shortcomings I see that there might be some impact overall, especially in the notebook segment. More at AnandTech


About krithik

An Electrical Engineer by training, who occasionally dabbles in programming and design.
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