the 7640u and 7840u are both rated for a default TDP of 28w, although it is configurable as low as 15w by the laptop manufacturer.

That reference seems to be using the default for the 7840u, whereas they’re using the configurable minimum for the 7640u, which is misleading.

The 7840u and 7640u are actually the exact same chip, just the 7640u has 2 CPU cores and 4 GPU cores disabled.

Ryzen is pretty good at putting cores to sleep when they aren’t needed, so when at idle or running a load that can’t take advantage of those cores the 7840u should behave pretty much the same as a 7640u and have similar power consumption.

Then when under heavy loads both CPUs will likely hit whatever the maximum power the cooler can handle is, however having more cores each running at lower power (ex. 7840u) generally performs better than fewer cores each running at higher power (ex. 7640u).

So under heavy loads the 7840u should actually have better performance with similar power consumption, however the better performance allows it to complete the task quicker and get back to low power idle sooner, overall improving battery life.

So theoretically the 7840u should overall have similar to slightly better battery life than the 7640u assuming all software is implemented properly (I was an early adopter of Ryzen 3000 desktop CPUs and it took several driver/BIOS updates before it would reliably put unneeded cores to sleep and significantly reduce idle/low load power consumption).

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credit: u/RiftBladeMC on Reddit and @[email protected] on Lemmy.

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