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Internet Message Format | 1998-08-03 | 6KB

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From: Russell King - ARM Linux Admin <[e-mail]>
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Subject: Re: [NetwinderLC General Forum] Re: Why Linux ARM
To: [e-mail] (Alex deVries)
Date:     Sat, 4 Jul 1998 10:06:27 +0100 (BST)
Cc: [e-mail], [e-mail]
In-Reply-To: <[e-mail]> from "Alex deVries" at Jul 4, 98 02:03:09 am
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Alex deVries writes:
> On Sat, 4 Jul 1998, Rasmus Lerdorf wrote:
> > To me, the fact that it is cheap, draws less than 20 amps and is quiet is
> > the main attraction.  I might be able to buy a laptop that is about the
> The fact that the Netwinder draws less than 20 amps isn't an attraction at
> all.  My refridgerator uses less.  What's more significant is that it uses
> less than 20 milliamps.

When you compare this with a PC (at work, we've had to measure the power
consumption of our PCs in a system we manufacturer to size a custom UPS)
of spec:

16MB RAM, 486DX4 100MHz, *No* hard disk, Flash/SRAM solid state card,
16 RS422 serial ports running at 38400 baud (and 10 in use), Video card
(Trident), Arcom PCSYSCON card.  No monitor connected.

which took over 4Amps 60 degrees out of phase with the power supply (I
think that the phase figure is correct), then this works out at around
480W in phase with the supply (yes, that's just an estimation).  The
powersupply got hot as well, and you could feel a nice breeze of warm
air blowing out the back.  (Oh, and I can quote quite a lot of horror
stories about fan failures on our normal PCs as well).

Although I don't have any figures for my ARM based machines here, I can
definitely say that they use a lot less power.  The only way that I can
say this is for the following fact:

1) EBSA-285 (with 3com 3c592 and S3 Trio64 added): the PSU has a
   temperature controlled PSU, and the fan is always running slowly.

2) EBSA-110: When the original PSU fan started being noisy (I hate noisy
   fans), I got a replacement from DEC, which at first reconnected to
   the +12V line in the PSU.  However, I thought why should I when
   the EBSA-110 takes no more than about 7W?  Now, it's connected to
   the +5V line and the PSU is still cool.  PLUS, DEC had to put a
   resistor on the PSU +12V line to keep the PSU in spec *because*
   the EBSA-110 takes so little power.

I haven't got the Netwinder figures here, but I bet that it's at least
an order of magnitude below a PC.

Hence, the argument should no longer be one of:

'A PC costs to buy 900ukp, but a RiscPC costs 1500ukp'

but more of:

'A PC costs xxx ukp to run each week, but a RiscPC costs yy ukp'.

Then you start to see where the real cost savings are with ARM technology.
Incidentally, the other advantage is that because it's not drawing a
lot of power, it's not getting hot, therefore:
 - electronic components are more reliable.
 - less need for mechanical fans which:
   - clog up with dust.
   - fail due to bearing wear.
   - clog up your floppy drive with dust.
   - when they fail normally take out the processor as well.

If someone wishes to dispute this, then I'll happily collect all the
figures together to prove it when I'm next at work.
   _____
  |_____| ------------------------------------------------- ---+---+-
  |   |        Russell King       [e-mail]      --- ---
  | | | |  http://www.arm.uk.linux.org/~rmk/armlinux.html    /  /  |
  | +-+-+                                                     --- -+-
  /   |               THE developer of ARM Linux              |+| /|\
 /  | | |                                                     ---  |
    +-+-+ -------------------------------------------------  /\\\  |

Buy a mobile for 1ukp and pay 100ukp per month line rental, or
buy a mobile for 100ukp and pay 1ukp per month line rental.  Which
would you prefer?  I know which one I'd like.
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