AMD Athlon64 4000+ Underclocking

Bios_Hakr writes "PC Stats is running an article on their experiences underclocking an AMD 4000+ processor. Their goal was to try and reduce the voltage requirements and lower the heat output. They benchmark using 3dMark01, 3dMark05, as well as SuperPi. From the article: 'This got us thinking though; what about under-clocking? Most modern processors and motherboards can just as easily run under a rated speed as it can run over... but is there a point to this? Well possibly.'"

Re:Umm....

[Xshare]

I think the point is that these "better" processors were built with that larger processor speed in mind, and if you underclock it, you still get the added benefit of somethign that's supposed to cool and use a bigger processor for a smaller one. It's like... AMD when they build the 4000+ over the 3200+, attempt to make the 4000+ as calm and quiet as possible, within limits, and go farther with the 4000+ than with the 3200+. Now if you underclock the 4000+, you still take advantage of that extra technology...

I'm probably wrong.

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Re:What's the point with passive cooling...

[TERdON]

Yes, I also realize this. Should have put an [/irony] at the end, perhaps. :)

My point was that in TFA (oops - we're on Slashdot, no one have read it) they use use some high-end Radeon and a motherboard with one of those annoying northbridge fans, mooting the point of a quiet CPU cooling setup alltogether. Not really the setup you (and I) are suggesting...

Underclocking for Gaming, Reverse Logic

[Anonymous Coward]

From 99-03 I always underclocked my AMD CPUs for gaming, the minimal requirements necessary for playing everyones favorite Counter-Strike, and my undying urge to make my CPU last ages kept my system running smooth, my latest underclocking was from a 2800+ 2ghz AMD down to a 1.87ghz miracle machine that ran on a minimal fan system, never overheated and my record uptime was 3 months and 2 weeks ;D

Re:Don't keep us in suspense

[pla]

it draws a whopping 54 watts average

Oops... Just to clarify, the entire system, including power supply losses, draws that much. The CPU itself, from what I've read (published numbers seem to vary a LOT, and I'd love to see some hard data on the min, mean, and max draw of the 90nm Athlon 64s), only eats between 7 and 35W (for comparison, the Pentium III line came in at the low 30s) with a theoretical max somewhere in the 60W range.


Kinda funny, actually... When everyone talks about needing bigger and better power supplies, with 400W considered a bare minimum and 600W not all that uncommon these days, I upgraded from an old P-III system and the total power consumption of the system dropped by half.

Fair comparison

[reversible physicist]

A key point here is that you can scale both the clock and the voltage. The power dissipated each time you get rid of a stored charge is proportional to the voltage squared. How often you do this per second depends on the frequency. Thus if you can run at half the voltage and one third of the frequency, then the processor dissipates 1/12 of the power!

A fair comparison of processors would be to calculate how much processing power you get in some benchmark per Watt of power dissipated: Fan noise for getting rid of CPU heat should be lowest when the least heat needs to be gotten rid of. Probably the processor with the best performance per Watt at full speed also has the lowest disspation per Watt at lower speeds.

I already did this back in 1980.....

[panurge]

Any other older-timers may remember the already very slow RCA 1802 CMOS processor. I used one of these in a home-made portable EPROM programmer, which allowed you to enter data from a keypad to make tiny patches to tiny machine code programs. To increase battery life, the thing was clocked using a 2MHz crystal (enough for the eprom programming) but when it wasn't burning, it ran on a 20KHz clock which was enough for the keypad data entry. The result was a power consumption in the low hundreds of microamps when idle, rather than 10mA or so. To those who say, why not just turn it off? I have to explain that in those days flash memory came in units of 64 expensive bytes. The battery power was necessary to keep the CMOS static RAM alive.

Thank you for letting me share this old-timer drivelling on slashdot.

Underclocking a '286

[SA Stevens]

A bunch of years ago I experimented with underclocking. I had an old AST 'Bravo' 286 machine and there wasn't much interesting to do with it. (I was running Slackware on a constellation of 386sx and better machines to fool around with networking). It had a socketed 'crystal block' TTL oscillator. I had a bunch of other oscillators around so I started plugging them in.

The base machine was as slow as an AT gets, it was a 6 MHz. 286. I plugged in a 1 MHz oscillator to make it a 512 KHz '286 machine. It actually booted up, very veeeery slowly. You could count the actual steps as the BIOS did the traditional 'step the floppy drive to one end and back' sequence.

Very nice!

Then I tried some even lower-value oscillators. I have block oscillators down to a value of 32.764 KHz. The machine wouldn't boot up at all at lower frequencies.

This is because the memory on the motherboard, and indeed the registers inside the CPU themselves, are dynamically refreshed. If the chip isn't run fast enough, it crashes.

There are processors that can run down to zero hertz, with an all-static CMOS design. The Intersil/Harris 6100 processor has this characteristic. You can use a knife switch as your clock if you wish.

Re:Umm....

[quarkscat]

A slower processor, say 1/2 the clock speed, would
not necessarily draw less power than the faster
processor running at that same speed. If you were
to compare 2 processors on the same die size, the
power required at a specific clock rate determines
what speed the manufacturer rates it for. Most
modern NMOS-type chip designs draw the most power
on the rising and falling clock edges.

The cleaner and sharper rise and fall times that
the processor clock runs at, the lower the power
requirements and the faster the clock could run.
Via and trace densities inside the chip determine
what the absolute maximum power can be drawn,
without melting (like a buss fuse). The faster
processor runing at a lower clock rate should
still have the steeper clock transition times,
drawing less power.

One of the requirements of a good chip design is
the use of a clock signal distributed well. So
long as a slower clock rate can still sync up
properly between on-chip modules (like caches),
a faster processor should draw considerably less
power than the slower processor, given the same
clock speed. Manufacturing tolerances determine
what a specific 6 inch or 9 inch silicon wafer
can produce, speed-wise. Of course, the more
faster chips that can be produced reliably from
a given wafer, the more $$$ the manufacturer can
make.

Processors designed for portable, low power use
already can make use of a slower clock when in
sleep mode. Desktop systems could also make use
of the same technology to save energy. A faster
processor that is running at a slower speed may
not even require a fan, if quiet operation is
desired. The motherboard design, mb support chips,
and the BIOS must support under-clocking for this
to work.

Just my rapidly depreciating $00.02 worth.