Screen resolution and battery life?

[gibson042]

VGA screens on existing and upcoming Pocket PCs range from a maximum size of 4.0 inches on the Toshibas and the HP iPAQ hx4705 to a minimum of 3.6 inches on the FSC Loox 720. It's obvious to me that having a larger screen will generally hurt battery life, but the 720 has a screen that's barely larger than the 3.5 inch QVGA standard! So I'm wondering, what kind of an impact will VGA resolution have on battery life, screen size considerations notwithstanding? A quick search didn't turn up any answers, but I suspect that there would be no noticeable difference between a QVGA and a VGA screen with the same dimensions and same backlight. Can anyone confirm or deny this?

[PJE]

I think this has been covered before:

If the screen were static, and did not need to be refreshed, the power useage would be roughly the same. However, the CPU is constanltly getting the screen data out of the memory and sending it to the display, thus it's moving four times more information to generate the display and this uses more power. It also needs to do more processing to generate the image which has four times as many pixels.

Hopefully the graphics co-processor in the new Axim X50 will handle some ot the scaling for the CPU and reduce - as far as possible - the performance and power consumption penalty of using the VGA display.

[gibson042]

I think this has been covered before:

If the screen were static, and did not need to be refreshed, the power useage would be roughly the same. However, the CPU is constanltly getting the screen data out of the memory and sending it to the display, thus it's moving four times more information to generate the display and this uses more power. It also needs to do more processing to generate the image which has four times as many pixels.

Hopefully the graphics co-processor in the new Axim X50 will handle some ot the scaling for the CPU and reduce - as far as possible - the performance and power consumption penalty of using the VGA display.

That all makes sense, but I thought that screen data and display management took only a very small fraction of a processor's power (especially with the faster processors we are now seeing)... do you know what the difference is in terms of device usage time?

[PJE]

That all makes sense, but I thought that screen data and display management took only a very small fraction of a processor's power (especially with the faster processors we are now seeing)... do you know what the difference is in terms of device usage time?

The faster the processor the quicker it can build the screen image - and with a graphic co-processor the loading on the CPU is further reduced. Once the image has been drawn the CPU throttles down until the next burst of activity.

For ebooks, and web pages etc.. if your eye sight is up for a smaller font you will have the benefit of fewer screen refreshes for a given amount of content.

As the Axim X50 is likely to be my next I'm hoping it is going to last as long as my X5 (without WiFi use) even though reportedly the standard battery is smaller (1100mAh vs 1400mAh).

The new VGA devices also have Bluetooth and WiFi which will have a much more pronounced effect on battery life than the VGA screen.

[newst]

Just a note from personal experience, and I'm not technically savvy enough to explain why, but back before SE was released, and the Toshiba E-800 was a dual mode PPC (switchable from VGA to QVGA) the power draw in VGA mode was significantly greater than QVGA, EVEN WHEN THE PPC WAS TURNED OFF!

There were technical reasons for this that you can no doubt find if you go to Brighthand and search their E-800 forum. Just relaying that there was greater power draw in the VGA mode even when the screen was not being refreshed.

[Janak Parekh]

the power draw in VGA mode was significantly greater than QVGA, EVEN WHEN THE PPC WAS TURNED OFF!
That would explain my symptoms, for sure. I always kept it in VGA mode.

--janak