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Subject: Re: DRAM 2MB -> DRAM 8MB


From: Vladimir Pantelic <>
Date: Mon, 16 Sep 2002 17:02:03 +0200

Stuart Tedford wrote:
> Excellent work.
> This mod should save a lot of battery power. Could you post the results
> when you get round to doing a test?

More RAM space for cool apps - YES

Doubled battery life - NO!

As we have a larger buffer to fill, the HDD has also to spin longer, so
nothing gained here. What we would gain is less time spent with drive
spinup if the buffer is 4x large.

Assuming we use:

50mA when the HDD is off
300mA when the HDD is running (reading 1MB/second)
500mA to spin up for 3secs

So with 2MB = 100secs of MP3 we have:
50mA + 300mA * 2/100 + 500 * 3/100 = 71mA average

and with 8BM = 450 secs of MP3 we have:
50 mA + 300mA * 2/100 + 500 * 3/450 = 59mA average
(not counting the extra current for the larger DRAM)

The average current is reduced only by about 20% by making the buffer
4x larger .....

These values are just rough estimates, but I just wanted to show that
a double buffer size does not make double play time.

For this you would have to make the current consumption of the rest of
the circuit much smaller.


Received on 2002-09-16

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