Question on laptops with desktop CPU's

[ribitch]

Do all of the laptops that are using a desktop P4 run at 1/2 speed while running off of the battery? Or is it only with a few manufacturers?

I read about this on slashdot and was kinda curious. Speed stepping is great and all, but if you use your laptop almost exclusively on battery power, why would you want to get a new P4 if an older system could potentially be faster in battery mode?

[ribitch]

so what is he purpose of making a laptop with a desktop cpu? sure you can kinda upgarde it, but not much. you take a major performance hit when unplugged. To me its just not worth it. Maybe if you stpeed down 200 -300 MHz, but not halving it.

Plus the manufacturers are really vague when talking about this.

It just caught me off guard when i read about it.

[i6s1]

The older chip running at full speed would use more power then a newer chip running at 2/3 speed.

Also, if you want full speed, you can change your speedstep mode, so it runs at full speed whether on battery or not.

AMD has an even better version, called powernow or something. It dynamically changes speeds depending on operating conditions. So it may run most of the time at low speeds, but when the cpu utilization gets high enough, it turns up to full speed. Best of both worlds.

I also thought that only the mobile chips can do speedstep. Is this true?

[LegendKiller]

Speedstep in the P3-M's does dynamically change the processor speed depending on processor utilization.

Manufacturers use desktop processors to drop costs. A 2.8ghz desktop probably costs 1/2 of what a mobile 2.7ghz notebook (or whatever the highest is now). Furthermore, ALL processors throttle down somewhat on notebooks when your running off of battery. The guy who complained on /. seemed like somebody who had no clue what was going on.


LK

[Jeffbx]

Like i6s1 said, it's a user selectable setting. You can set it so you always run at full clock speed whether you are on battery or not. Also, if I remember correctly the default setting is that the processor will only clock down during idle periods. Once you start to run a processor intensive app it will ramp back up to full speed.

[Devhux]

Actually, Speedstep is a feature on the P4-M chips, not the desktop P4's.

Desktop chip-based laptops are meant for those who will primarily be using their machines as a destop replacement, and hence will have the unit plugged in most of the time. If the chip was running at full speed on battery mode, you'd be lucky to get 60-90 minutes of battery life. Then again, with the beefy batteries found on such notebooks, you wouldn't want to be lugging them around much anyway. Desktop P4 chips still use a substantial amount of power compared to their mobile counterparts, which is why such large batteries are required.

[spigidygak]

You all missed the main point. Reason there are desktop cpus in laptops is . . . MONEY MONEY MONEY. Its a lot cheaper for them to slap in a desktop cpu than a mobile cpu since they're easier had. And not sure if it still applies but the desktop cpu would be slower than the same speed mobile cpu. Also just 'cause its a desktop cpu doesn't mean you can switch it out. In most cases they are still soldiered in.