PowerBook 12" clock battery?

This says it has no backup battery, just a capacitor to maintain PRAM setting long enough to swap batteries if not connected to AC:

http://support.apple.com/kb/TA25911?viewlocale=en_US

It really doesn't have a PRAM battery? Wow. That's kind of insane.

tom

Tradeoffs: you get rid of battery failure/leakage problems, in exchange for losing PRAM settings if you let the main battery go completely dead while disconnected from mains. (Which most people seem to not do often, if at all.)

That problem might go away of the PRAM was static RAM of some sort, but that probably wasn't a cost-effective option at the time of design.

The battery failure problem is a bit of a red herring: without a PRAM battery, you effectively have a battery failure every time the main battery runs out! As for leakage - how often is that a problem? I don't think i've ever heard of it happening to anyone i know.

I suspect the main reason was to drive down costs and save space inside the case, which in a 12" machine is at an absolute premium.

That problem might go away of the PRAM was static RAM of some sort, but that probably wasn't a cost-effective option at the time of design.

Very true. I wonder if we'll start to see machines shipping with a small chunk of flash memory soldered onto the motherboard instead of battery-backed RAM. Possibly not, because of the much more complicated circuitry needed to control it. Plus, you still need a battery to keep the clock running. Although if we also start to get ubiquitous GPS, then since GPS gives you a highly accurate time, we might not need independent clocks at all. Although you'd be a bit stuffed if you were somewhere out of GPS reception.

tom

Not really. One common problem with old laptops is the PRAM battery dying. Since they are expensive and hard to access not having one is a plus.

The PRAM memory IS Static. But static memory still needs power. You could use flash but you still need power for the clock. And a few Kb of static RAM takes very little power, far less than the clock.

If they used a super cap it could probably run the PRAM / clock for a few days without battery or mains power.

No! Because the result of not having one is that you suffer the symptoms of a dead battery (clock not surviving a flat battery, not being able to change battery while sleeping, etc) ALL THE TIME. What you're saying is analogous to saying that because a common problem with old people is arthritic knees, not having any legs is a plus.

tom

You CAN change the battery while sleeping without loosing PRAM settings and the clock without a PRAM battery, that was pointed out earlier.

You shouldn't let your main battery go flat, it's bad for the battery and if the computer is asleep, it's bad for the computer. That is more serious than your clock going bonkers.

Your analogy is bogus.

batterie packs are designed to shut off before damage can occur.

and if the computer is asleep, it's bad for the computer.

how so? if the battery is discharged beyond a certain point, the computer won't wake up until it's plugged in.

And the safeguards *always* work, don't they?

By then it's not waking up so much as being raised from the dead.

I've never heard either of those assertions before; could you direct me to more information on them?

tom

Considering that Apple explicitly recommends that notebook batteries be drained a few times a year to recalibrate the user feedback system, I doubt he'll be able to provide an authoritative source.

<http://support.apple.com/kb/HT1490>