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Does RAM size affect battery life?

Message #1 - Posted 2003/10/24 - Hobo

I have a 2001 iBook w/ 576 MB RAM. I would love to see the iBook last longer than the current 2-3 hours while on battery. If I used less ram, say around 200MB, would I get longer battery life?

Message #2 - Posted 2003/10/25 - Gregory Weston

Previously, Hobo wrote:

I have a 2001 iBook w/ 576 MB RAM. I would love to see the iBook last longer than the current 2-3 hours while on battery. If I used less ram, say around 200MB, would I get longer battery life?

If you're running OS X, there's no real way to "use less RAM." Unused RAM is just a waste, and the OS will use anything not actively spoken for as disk cache.

G

Message #3 - Posted 2003/10/25 - John Johnson

Previously, Gregory Weston wrote:

Previously, Hobo wrote:

I have a 2001 iBook w/ 576 MB RAM. I would love to see the iBook last longer than the current 2-3 hours while on battery. If I used less ram, say around 200MB, would I get longer battery life?

If you're running OS X, there's no real way to "use less RAM." Unused RAM is just a waste, and the OS will use anything not actively spoken for as disk cache.

G

Of course, removing RAM from your machine will improve battery life. Whether it improves it enough to compensate for the disadvantages is another question. Many people over in comp.sys.mac.portables say that 512MB RAM is the minimum for OS X 10.2.* I'm running it in 384MB on a Pismo 400 and it works fine. When I moved from 192 to 384, I noticed significant speed improvement.

Several other factors influence your battery life. Newer versions of OS X are better with the battery than old ones. Again, I noticed improvements when I moved to Jaguar from 10.1.4. Screen brightness, AirPort, disk access, devices, and battery age can affect your battery life. You may just be noticing a battery that is beginning to lose some capacity with age/cycles. If you discharge and recharge your battery often, it loses capacity faster; that's just the way batteries work. Your battery certainly isn't dead, though.

Summary: going below 384MB RAM is not a good idea, IMO. Check your energy saver settings. If you are running OS X 10.1.*, go out and buy Panther (10.3). Your machine supports it, it will almost certainly make the machine feel faster and give you better battery life as well. Plan on replacing the battery in another year or so. It might last longer, but if you keep the machine long enough it will keep losing capacity until it's not usable.

HTH.

Message #4 - Posted 2003/10/25 - Kirk Strauser

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At 2003-10-25T18:05:38Z, John Johnson <null@invalid.com> writes:

Of course, removing RAM from your machine will improve battery life.

You state that as a given. My guess would be the opposite: removing RAM increases the likelihood of swapping, and an active hard drive consumes much more power than a few DRAM chips.
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Kirk Strauser
The Strauser Group
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Message #5 - Posted 2003/10/26 - John Johnson

Previously, Kirk Strauser wrote:

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At 2003-10-25T18:05:38Z, John Johnson <null@invalid.com> writes:

Of course, removing RAM from your machine will improve battery life.

You state that as a given. My guess would be the opposite: removing RAM increases the likelihood of swapping, and an active hard drive consumes much more power than a few DRAM chips.

Pardon me for not being precise enough.

"Of course, removing RAM from your machine will reduce the power draw from RAM. If you don't need that extra RAM, this can improve your battery life. However, removing RAM might cause you to swap more often,...etc."

Without thise extra precision, I realize that the comments made immediately afterwards about recommended RAM minimums, and my summary, must have seemed contradictory. My apologies.

Message #6 - Posted 2003/10/26 - David C.

John Johnson <null@invalid.com> writes:

Of course, removing RAM from your machine will improve battery life. Whether it improves it enough to compensate for the disadvantages is another question.

Assuming you don't need the RAM, yes. If your apps need it, you'll start swapping. Hard drive uses more power than RAM.

Many people over in comp.sys.mac.portables say that 512MB RAM is the minimum for OS X 10.2.*

IMO, that's a bit overenthusiastic.

The 128M that Apple claims to be a minimum is unacceptable.

192M, I'm told, is acceptable, but slow.

256M is what I consider an actual minimum.

512M is what I consider preferred.

More shouldn't hurt. Depending on the price for the kind of memory you need, I recommend maxing-out whatever system you're using.

Several other factors influence your battery life. Newer versions of OS X are better with the battery than old ones.

In general. But I know of one person who has seen degradation on his 17" PowerBook after upgrading from 10.2.6 to 10.2.8. (And yes, he installed the updated 10.2.8 - the original 10.2.8 was absolutely lousy. The updated one still isn't as good as 10.2.6, however.)

-- David

Message #7 - Posted 2003/10/26 - John Johnson

Previously, John Johnson wrote:

Previously, Kirk Strauser wrote:

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At 2003-10-25T18:05:38Z, John Johnson <null@invalid.com> writes:

Of course, removing RAM from your machine will improve battery life.

You state that as a given. My guess would be the opposite: removing RAM increases the likelihood of swapping, and an active hard drive consumes much more power than a few DRAM chips.

Pardon me for not being precise enough.

"Of course, removing RAM from your machine will reduce the power draw from RAM. If you don't need that extra RAM, this can improve your battery life. However, removing RAM might cause you to swap more often,...etc."

Without thise extra precision, I realize that the comments made immediately afterwards about recommended RAM minimums, and my summary, must have seemed contradictory. My apologies.

Let me reply to myself. I was grumpy when I wrote this, and it shows. Sorry about that.

I attempted to provide a brief summary of some of the issues surrounding RAM and power. I did leave out the bit about swapping as a result of not having enough RAM, and thank those who pointed this out.

My approach was to recommend enough RAM as a minimum that the OP would be unlikely to run into gratituitous swapping. I run with 384, and certainly wouldn't want to run with 192 again. Avoiding swapping is important both for energy conservation and system responsiveness, so having enough RAM to avoid this should IMO, be a higher priority than simply conserving power.

As shamino@techie.com pointed out, somewhere between 256-512 seems to be a good operating range. Whether someone needs/wants more or not depends on many other factors, and I can't speak to it.

As for the comments about 10.2.8 hurting battery life, I'm not surprised. I did make a generalization about more modern OS versions, and that didn't include that particular release (which should IMO, be avoided, particularly with Panther available).

This has been a good discussion, sorry for the grumpiness.

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