Temperature monitoring on old desktop - Dell OptiPlex SX270?

Jeremy Chadwick koitsu at FreeBSD.org
Sun Aug 3 13:43:29 UTC 2008

On Sun, Aug 03, 2008 at 01:52:51PM +0200, Torfinn Ingolfsen wrote:
> On Sat, 02 Aug 2008 20:19:12 -0700
> Jeremy Chadwick <koitsu at FreeBSD.org> wrote:
> > On Sun, Aug 03, 2008 at 01:50:53AM +0200, Torfinn Ingolfsen wrote:
> > The first questions to ask are: 1) does this machine even have a H/W
> > monitoring IC on it, and 2) is it enabled/wired to thermistors and
> > fans?
> Yes, but so far I haven't found out anything by searching.

Then the only possibility is to take a very high-resolution photo (read:
2048x1536 or higher) and send it to someone who can identify ICs (I'm
good at recognising H/W monitoring ICs :-) ).  But even that won't
guarantee anything; an IC that supports H/W monitoring may be
found/present but it may not be wired to support such (or the board
lacks thermistors), or possibly the silkscreening is false (which I
myself have personally seen on some server boards).

> Ok, so what is the 'TM' feature of this cpu then?
> cpuid thinks it is a thermal monitor:
> Intel-specific functions:
> Version 00000f29:
> Type 0 - Original OEM
> Family 15 - Pentium 4
> Extended family 0
> Model 2 - Intel Pentium 4 processor (generic) or newer
> Stepping 9
> Reserved 0

This gets into semantics: "what exactly does 'monitor' mean?"

The P4 TM feature is more of a thermal manager and not so much a
"monitor" in the sense of what you think it might be (re: ability to
provide thermal statistics to a program).  It *is* a "monitor" in the
sense that it reads temperature, but there's no way to access that
internal data.

I believe the P4 TM is used to decrease power usage (disabling some
features, enabling some power-saving modes, etc.) based on temperature.
It probably induces some form of clock throttling too, but it's probably
done very differently compared to present-day Core2Duo processors, for
example (and those processors DO have on-die per-core temperature
monitors which you can monitor, re: coretemp(4)).

Here's some reference material confirming my claim:


The point is, none of the internal data is accessible.  I have never
seen a program provide any sort of thermal data on a P4, unless there's
an external H/W monitoring IC (with a thermistor that sits physically
under the processor mounting socket) installed.  You'll find such
features on P4 server boards -- commonly Winbond ICs, with a thermistor
that sits directly under the CPU.

> > I just checked http://tingox.googlepages.com/sx270 and sure enough, an
> > older P4.  coretemp(4) won't work with this.
> I know, I just thought that ther might be something similar for the TM feature of Pentium 4's.

Nope, because it's not something you can get data from.

> > I would start by booting the machine into Windows and install
> > SpeedFan.  If that thing is able to detect and provide thermal data,
> Ouch. I was hoping that I wouldn't have to do that. The machine have no internal CD-drive,
> and for some reason doesn't want to boot from a (usb) external cd-drive either (kind of funny - it boots from flash drives and external hard drives. But cd-rom -no).
> I was hoping to solve this without windows in the picture.

You could try Linux.  Their lm-sensors project is incredibly thorough,
but based on what I've looked at in the code, it's hit-or-miss.  It does
do a form of auto-probing (which is very risky IMHO).  Speedfan's
auto-detection method is better, and safer (especially if there's an
SMBus interface with H/W monitoring IC tie-ins made available).

Again, this would only allow you to detect whether or not there's an
actual H/W monitoring IC on the board somewhere.  I'm strongly doubting
there is.  You could contact Dell and ask, but their Support folks
probably have no idea what a hardware monitoring IC is (or will lie to
you and say "Yes it has it" even though it may not).

| Jeremy Chadwick                                jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |

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