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How much sleep load per MB of RAM?

Message #1 - Posted 2005/08/25 - Peter Renzland

In <42b75fd8@news-1.oit.umass.edu>
Subject: Re: "ramBunctious" SEEMS like a good idea - - - Opinions? On 2005-06-21 Joe Heimann wrote:

I suspect Apple did not do so because RAM that meets their specs for power usage in sleep mode does not consume all that much power. From the developer notes for the 15" PB, they specify that RAM should not use more than 6 mA/128 MB from the 2.5 V power supply. At a max RAM of 2 GB, that translates to about a .25 W, not a very large draw. Those are typical figures in the specifications for other Apple notebooks as well.

16 * 6 *2.5 = 16 * 15 = 240 mV

So, at 512MB, my IBook G4 should soak up . . .

First, my battery is about 4 times the Voltage (11V - 12V) roughly. So presumably it should take no more than 1.5 mA / 128 MB, right?

My old G3 with 640 MB took about 15 mA in sleep.
Hm. That's about *twice* that.

Let's check the new G4:

In 3.5 hours it went down by 60 mAh. 17mA.

So, I'd like to buy a further 1GB.
Does that mean my sleep drain will then be three times as much? 51mA? That means 24h sleep will burn up 28% of my brand new battery.

Here's another question:

If I buy cheap RAM, might it consume more power in stand-by mode?

I'm thinking of buying this:

http://www.kingmax.com/news/news_product/news_p20041130.htm

It costs about 1/4 of Apple's RAM.

-- Peter ( renzlandATgmailDOTcom )

lineeaterlineatereatupthisline

Message #2 - Posted 2005/08/25 - Joe Heimann

Peter Renzland wrote:

In Subject: Re: "ramBunctious" SEEMS like a good idea - - - Opinions? On 2005-06-21 Joe Heimann <heimann@ecs.umass.edu> wrote:

I suspect Apple did not do so because RAM that meets their specs for power usage in sleep mode does not consume all that much power. From the developer notes for the 15" PB, they specify that RAM should not use more than 6 mA/128 MB from the 2.5 V power supply. At a max RAM of 2 GB, that translates to about a .25 W, not a very large draw. Those are typical figures in the specifications for other Apple notebooks as well.

16 * 6 *2.5 = 16 * 15 = 240 mV

That should be .24 W or 240 mW, not 240 mV.

So, at 512MB, my IBook G4 should soak up . . .

First, my battery is about 4 times the Voltage (11V - 12V) roughly. So presumably it should take no more than 1.5 mA / 128 MB, right?

That is correct, if you assume 100% efficiency in the conversion of the 12 V inside the PB to the 2.5 V used to maintain the RAM. There is also some other draws in sleep at their own voltages and conversion efficiencies, so the total current usage will be higher.

My old G3 with 640 MB took about 15 mA in sleep. Hm. That's about *twice* that.

Your old G3 used more chips per 128 MB to get to that total of RAM. So a higher total current usage is not unreasonable to expect for each 128 MB in the G3.

Let's check the new G4:

In 3.5 hours it went down by 60 mAh. 17mA.

So, I'd like to buy a further 1GB.
Does that mean my sleep drain will then be three times as much? 51mA? That means 24h sleep will burn up 28% of my brand new battery.

Some of that 17 mA is used by the RAM, the rest goes to losses in the regulated voltage supplies for the different supplied currents and whatever else uses power in sleep mode. I suspect tripling the RAM will not drain three times as much, probably closer to double. So you should get about 5 days in sleep mode, if you were going to leave it that way for the entire time.

Here's another question:

If I buy cheap RAM, might it consume more power in stand-by mode?

Cheap RAM sometimes is made with less expensive, more power hungry components. But you can't always tell ahead of time, depends on how extensive the specifications the maker of the RAM makes available.

I'm thinking of buying this:

http://www.kingmax.com/news/news_product/news_p20041130.htm

It costs about 1/4 of Apple's RAM.

From the description it should be low power consuming RAM, just check to see it meets all the other specs for your PB. There are some that specify what internal data organization is used in the chips and the like.

Joe

Message #3 - Posted 2005/08/26 - Peter Renzland

In <430e9399@news-1.oit.umass.edu>
On 2005-08-26 Joe Heimann wrote:

Peter Renzland wrote:

Here's another question:

If I buy cheap RAM, might it consume more power in stand-by mode?

Cheap RAM sometimes is made with less expensive, more power hungry components. But you can't always tell ahead of time, depends on how extensive the specifications the maker of the RAM makes available.

I'm thinking of buying this:

http://www.kingmax.com/news/news_product/news_p20041130.htm

It costs about 1/4 of Apple's RAM.

From the description it should be low power consuming RAM, just check to see it meets all the other specs for your PB. There are some that specify what internal data organization is used in the chips and the like.

Thanks Joe. One more question -- how do I go about checking to see that it meets those other specs? I found this very detailed spec sheet for the above memory: http://www.kingmax.com/support/Kingmax_DDR_SO-DIMM.pdf

On page 11 it says:

Pre charge power down standby current: 80 mA (for the 1GB)

That looks like what I'm looking for.
That would mean (modulo losses and other loads)
an additional 20mA (+ the 17mA with native RAM).
That's consistent with your estimate of "double".

So, looks like I'll go and get it. :-)

(The G4 already has 3 swap files doing almost nothing.)

-- Peter

Message #4 - Posted 2005/08/27 - Peter Renzland

So here are my findings for sleep load for 1.33Ghz G4 iBook:

RAM Current Power
.5GB 15.5 mA .2W
1.5GB 25 mA .3W

low load .8A 10W (invariant of RAM)

So, with the 50Wh battery, and with 1.5G RAM,
it could sleep for for almost a week.

-- Peter

Message #5 - Posted 2005/09/09 - Joe Heimann

Peter Renzland wrote:

In <430e9399@news-1.oit.umass.edu>
On 2005-08-26 Joe Heimann wrote:

Peter Renzland wrote:

Here's another question:

If I buy cheap RAM, might it consume more power in stand-by mode?

Cheap RAM sometimes is made with less expensive, more power hungry components. But you can't always tell ahead of time, depends on how extensive the specifications the maker of the RAM makes available.

I'm thinking of buying this:

http://www.kingmax.com/news/news_product/news_p20041130.htm

It costs about 1/4 of Apple's RAM.

From the description it should be low power consuming RAM, just check to see it meets all the other specs for your PB. There are some that specify what internal data organization is used in the chips and the like.

Thanks Joe. One more question -- how do I go about checking to see that it meets those other specs? I found this very detailed spec sheet for the above memory: http://www.kingmax.com/support/Kingmax_DDR_SO-DIMM.pdf

On page 11 it says:

Pre charge power down standby current: 80 mA (for the 1GB)

That looks like what I'm looking for.
That would mean (modulo losses and other loads)
an additional 20mA (+ the 17mA with native RAM).
That's consistent with your estimate of "double".

So, looks like I'll go and get it. :-)

(The G4 already has 3 swap files doing almost nothing.)

-- Peter

My news server just finally downloaded your last message, so I was not ignoring you. So, yes, that does look like the RAM will work and not add too much additional load. Given the couple of weeks that have passed, how did it go?

Joe

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