[lca2018-chat] Arjen's new laptop

[James Henstridge]

On 29 January 2018 at 18:58, Arjen Lentz <arjen at openstem.com.au> wrote:
> Hi James
>
>> On 29 January 2018 at 17:38, Arjen Lentz <arjen at openstem.com.au> wrote:
>>> It has a quad core Intel i5 8250U 1.6GHz (turbo to 3.4GHz) which is a quad core
>>> + hyperthreading.
>>> Why not an i7? Because you will mainly kill your battery life, in return for
>>> very little extra performance - remember it's a mobile CPU infrastructure.  A
>>> desktop replacement approach will always be bigger, heavier and eat more power
>>> (been there, tried that).
>>
>> Are you sure about that?  If it was an i7 from the same range, it
>> would likely have the same TDP as the i5 models.  At least for the
>> mobile chips, the i5/i7 branding mostly looks like a case of picking
>> and market differentiation rather than being completely different
>> products.
>
> I didn't mention thermal?

The TDP is generally a good measure of the power usage of a chip.
Most of the electrical energy is eventually converted to heat, so it
is a reasonable measure of the input power too.


> I raised two aspects:
>
> a) This quadcore i5 performs pretty well. I expect that an i7 which has higher clockrate and more caching also chews more power, and that has a direct effect on battery life.

Well, things are a little more complicated with power management.
Both chips probably have similar power requirements in low power
states.  And the faster CPU could potentially finish its work in a
high power state quicker.  A larger cache might also mean the CPU can
do more without waiting on RAM, allowing it to enter low power state
quicker.  So it isn't always clear cut.


> b) Typically, a desktop replacement uses desktop (not mobile) component architecture and infrastructure. While that provides desktop performance, again your battery life will suffer. It's a trade-off. This laptop is not a desktop replacement, and thus I do not expect it to be as performant as my snazzy desktop machine.  They each have their purpose. For me, a laptop becomes much less useful when the battery doesn't last.
>
> I'm a tad confused as to what aspect your response addresses.
> Are you disagreeing with my basic analysis, and if so where?
> thanks

Looking at your processor in the list on Wikipedia, there are i7
variants with very similar configurations:

https://en.wikipedia.org/wiki/Kaby_Lake#Low/Medium_power_2

If your laptop was offered with an i7 chip, it was likely one of these
rather than a desktop derived chip.

James.