memory power usage q

[doctor bloomquist]

In my T23, I've got one 512mb chip and one 256mb chip. I'm thinking of replacing the 256 with another 512.

I know that as you add more memory the battery life is reduced, but is this because the slot is filled or because there's more memory?

I mean, if the chip is 3.3volts, does the amount of memory on it matter? Both the 512 and 256 are still drawing 3.3 volts right? If the 512 draws more power than the 256, does anyone know how much battery life is reduced, neglible/ a lot?

[ajkula66]

The loss in battery life would not be noticed by most people. You will notice when you max out the RAM in a good way, though.

[rkawakami]

Actually the amount of power that is consumed by a memory module is dependent upon the type and number of individual memory "chips" that are on the module. It's not necessarily true that a larger memory module will demand a proportionally larger amount of power. For example, if you have a 16-chip 256MB module and replace it with a 16-chip 512MB module, the power requirement will not double. In fact, it might even decrease. How's that? Newer memory designs (i.e., larger array sizes) typically use a smaller design rule geometry; the memory cells are smaller and thus require less power.

You would have to obtain the manufacturer's datasheets on the modules in question before you could determine whether or not there's a significant difference in the amount of power (current) they draw. I'd say a worse case difference would be in the area of about 500mA. That works out to almost 5.5 watts; quite a bit of a change when running on battery. A brand new T23 battery is designed to deliver about 40Wh (watt-hours). Increasing the power by 5 watts means 1/8 less time, or roughly 15 minutes if the battery "normally" lasts 120 minutes.

Here's a good example of what I was talking about earlier about a larger module taking less power:

http://download.micron.com/pdf/datashee ... 4x64HG.pdf

This is the Micron datasheet for the 256MB and 512MB PC133 SODIMMs. If you look on pages 12 and 13, the "Operating Current" in Tables 11 and 12 show that the 256MB module is rated for a maximum of 1216mA for the "-133" version and the 512MB module is rated for a maximum of 1016mA, also for the "-133" version. This means that the 512MB module generally requires less current (power) than the 256MB module; 200mA, which means about 6 minutes more "life" by my calculations.

edit: I need to clarify the current limits as published in the datasheet. These are maximum limits that the module is rated for. They will typically draw less power than the maximum limit. How much less depends upon many factors; the speed of the system the module is used in, the temperature they operate at, the amount and types of programs running in memory, etc.). Taken as a general guideline however, you would be safe in assuming that for at least these two Micron modules, the 512MB will consume slightly less power than the 256MB, all other variables remaining the same.