i386 version in future ?
galtsev at kicp.uchicago.edu
Wed Sep 28 14:56:05 UTC 2016
On Wed, September 28, 2016 3:54 am, Ralf Mardorf via freebsd-questions wrote:
> On Wed, 28 Sep 2016 00:59:09 -0700, Mehmet Erol Sanliturk wrote:
>>You are comparing different CPU brands with each other .
> It's unrealistic to compare 32 bit and 64 CPUs, produced with the same
level of development. Could you provide some examples?
> Actually I'm comparing two CPUs from the same family. The CPU I'm using
for my desktop computer today and the last 32 bit CPU I used for my
desktop computer before I switched to 64 bit.
> My old 32 bit was an Athlon single core 800, 850 or 900 MHz, I don't
remember exactly, Socket A, so the consumption was between >= 42.6 W and
<= 49.7. My current, newer 64 bit dual core is an Athlon BE-2350, 2100
MHz, Socket AM2, 45 W.
>>Assume that two CPUs are produced with the SAME technology .
>>A 64 bit CPU will contain more circuits than a 32 bit CPU , means more
power it will use because amount of power will be proportional to number
of circuit components and length of connection lines .
> But they are not produced with the same technology, the 32 bit
> Athlon I mentioned requires 1.70 V or 1.75 V, the 64 bit Athlon I
mentioned 1.25 V, they are anyway from the same family, they were just not
produced with the same level of development.
This is true: the power goes mostly into charging and discharging
capacitances associated with FET gates (ans stray capacitances). Energy
associated with charge is (C*(U)^2)/2. If we use half of voltage this
energy drops 4 times! (hence consumed power drops 4 times). This is why
the highest frequency part (core) works at lower voltage than the rest of
CPU. Now, there is also capacitance C in that formulae, which roughly
speaking is proportional to gate area (it is more sophisticated, yet...).
So, the technology goes to twice as small nanometers (which are linear
dimensions of elements), then the capacitance diminishes 4 times. That is
why it only makes sense to compare "the same technology". Next, the CPUs
are more sophisticated than just a width of arithmetic unit which for 64
bit would be twice than for 32 bit if CPUs were trivial devices. Actually
it is not quite so, thus processing some amount of 32 bit CPU work on 64
bin CPU will (considering the rest equal) not require to spend twice the
energy as compared to 32 bit CPU. You will spend more energy, this is
correct, but not two times more. (Very crude analogy here is: powering off
unused CPU cores; somewhat parallel utilization of components of 64 bit
CPU when processing 32 bit stuff probably is less crude way of saying it).
Anyway, thanks, everybody for refreshing and very insightful discussion!
> The slower CPU, slower RAM, different hardware, IDE etc., made the old
computer almost half as fast, so it needs to run almost double the time,
to reach the same processing power.
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Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
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