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Copyright © 1998 by Fabian Pascal. All Rights Reserved

32Bit Computing

By Fabian Pascal

Hard to Keep Your Cool

With increasingly faster systems, temperature control is becoming becoming more important. Faster CPUs, buses, graphics cards and drives generate more heat and require proper cooling. Witness the plethora of Web information on a variety of increasingly sophisticated cooling devices and techniques (all the way to cryogenics), including sites dedicated entirely to this subject.

Temperature control requires temperature monitoring. Yet all the cooling sophistication notwithstanding, the PC industry must still get its act together on basic monitoring.

This article discusses monitoring requirements for a system and offers some practical recommendations.

CPU Fans

Beyond 300MHz, CPUs in general, let alone overclocked ones, must be properly cooled. Pentium II (PII) CPUs come with basic coolers consisting of a heatsink and one fan. While for speeds of up to 300MHz they are sufficient, it is advisable to get a more powerful cooler for faster CPUs.

The better PII coolers come with a bigger heatsink and two fans. Tennmax's VIVA (www.tennmax.com), for example, has a unique advantage, explained by Vincent Tzeng of TennMax as follows:

"The interface material on the VIVA cooler is a TennMax proprietary materials, T-Pad. It is highly thermally conductive and will soften above 45 degrees Celsius, becoming "comfortable" to enhance thermal conduction between the sink and the CPU, which usually has "micro surface defects".
Those defects can trap air pockets between the mating surfaces. The T-Pad becomes gummy when the temperature raises above 80-90 degrees. But unlike many other "phase change" materials, it will retain its physical integrity under high pressure and high temperature (way over 100 degrees Celsius). It will, however, revert back to its original elastomeric state when the temperature falls back to 40 degrees or lower, so when the user removes the cooler off the CPU, there is a clean break and no need to reapply the interface material."

Overclocking, however, requires larger heatsinks and fans, such as, for example, those of Global WIN's VEK-12 cooler (www.globalwin.com) and there are even larger coolers with three fans.
But even with an effective cooler, not monitoring the CPU fans is risky, particularly on Slot 1 boards, which make the CPU temperature monitoring itself less likely (see below).

As a concrete example, when the CPU fan connector on my system board failed for an unknown reason, both the cooler's fans stopped working. Luckily, I had to open the case for another reason and happened to notice it (although I do not know how soon after the problem occurred I noticed it). This could have damaged the CPU even without overclocking, but I was running a "Klamath" PII/300 at 100x3.5=350MHz at the time, overclocking both it and the bus! A fan monitoring facility would have issued an alarm when the fans stopped. Even if the CPU temperature were monitored -- it wasn't -- this would be safer than waiting for the temperature increase to trigger an alarm.

System boards provide only one connector for the CPU cooler, to which both fans must be connected with one wire. That means that if one of the fans fails (which is what Murphy's law says will happen), a monitoring facility won't detect it. The VEK-12 can be connected to either one, or two places on the board, if they are available and within reach (which may defeat the monitoring of a case fan, see below) .

Coolers for Super7 CPUs (e.g. Cyrix MII and AMD K6-2), such as TennMax's Ultra -- have only one fan, but monitoring is not guaranteed (see below).

Case Fans

All cases come with a power supply fan, but vary on the number of additonal fans, how many are standard/ optional and whether they connect to the system board (3-pin) and can be monitored, or to the power supply (4-pin) and cannot be.

For example, California PC Products's minitower case (www.calpc.com), has two optional fans in front, under the drive bays, which normally connect to the power supply; fans connecting to the system board are available, but must be ordered explicitly. AProImage's tower case (www.aproimage.com) has three fans, one standard on the back, above the power supply, and two optional in front, under the drives, but they all have power supply connectors. Other cases I've seen accept two optional fans with power supply connectors, or take up to five optional fans, four on the sides of the drive bays (two on each side) and one in front, but only one can be ordered with a system board connector that can be monitored.

As far as I can tell, the standard power supply fans come with 4-pin connectors and, therefore, unless the vendor agrees to provide a 3-pin connection, they cannot be monitored.

Drive Fans

Proper air flow and cooling must be provided for 10,000rpm hard drives (and is advisable for even 7,200rpm), even if only to prolong their lives; a $20-$35 expense for a drive cooler to protect a >$600 drive certainly makes sense.

Tests of the various drive cooling devices available suggest that their effectiveness is similar and they vary mainly in looks, installation and price. California PC products offers the basic BayCooler, which has two front fans and a grilled bezel which makes it more esthetically pleasing.
Global WIN's KingKong is not as pleasing to the eye (the front fans are exposed), but has three fans and its black metal enclosure also serves as heatsink, for better heat dissipation. They also offer the I-Storm, which is quieter and also helps circulate the air in the case, but it protrudes from the face of the case ( the California PC case has a door and cannot be closed with it installed).

The fans on drive coolers comes with 4-pin connectors and cannot be monitored. The less esthetical fan exposure of the King Kong enables visual detection of fan failure. Other than that, the user must hope for the best (see conclusion).

System Board Fan Support

System boards vary on the number of fan connections they allow, as well as on their location. Abit's BX6 board (www.abit-usa.com), for example, has three fan connectors, one near the CPU, one between the CPU slot and the RAM DIMMs, above the power supply connector; and one on the corner underneath the DIMMs. Since the power supply fan does not connect to any of them, this allows for two case fans to be monitored (or one, if two CPU fans are monitored). The fans that came with the California PC's case had 4-pin connectors, but luckily my integrator, Digital Systems Innovation (www.dsi2000.com ), had a 3-pin replacement with enough wire to reach one of the connectors; but not the other. Besides, when the CPU fan connector went bad, I had to use the other connector for the CPU, so I ended up monitoring only one case fan.

Abit's newer BH6 system board has only two fan connectors, of which one is available for a case fan. But the board is a tad smaller, just enough for the 3-pin fan's wire not to reach it anymore.

The AOpen AX59Pro Super7 board (www.aopenamerica.com) comes with a 3-pin connector for only one fan, on the corner under the ISA slots.

Monitoring Software

Even if there are enough connections for all the fans on the system board and all fans have 3-pin connectors that reach the board (which is not likely), monitoring is still not guaranteed.

There are several monitoring programs available, some of which do not work under NT. Of the couple of NT-compatible programs, I prefer MotherBoard Monitor (www.euronet.nl/users/darkside/mbmonitor), for its features set and user interface. It resides in the system tray and is capable of monitoring system voltages; four temperatures: CPU, system board and two other user- defined sensor locations (see below); and the speeds of three fans (see Figure 1)

Figure 1: Motherboard Monitor

But to do their job, such programs must access special chips on the system board, which vary across boards. MotherBoard Monitor supports the LM78, LM75, LM79, or Winbond chips. According to its developer, Alex van Kaam:

"Originally, Socket 7 system boards had the LM78 chip connected to the ISA bus and the LM75 connected to the system management bus (SMB). (LM79 is a LM78 with some smaller changes). The LM78 can monitor one temperature, three fans, five positive voltages and two negative voltages; the LM75 can monitor just one temperature. Since the CPU was on the board itself, it was easy to just put a LM75 sensor underneath it to compensate for the thickness of the CPU.

When the Slot 1 systems with the CPU off the board came out, the LM75 got dropped. At that same time, Winbond developed their W83781D chip, which was nothing more then a LM78 with two more banks which point to the possible location of two LM75 sensors. Thus, instead of having to access the SMB and search for these sensors, monitoring programs can now let the Winbond chip do it and read the results of the two extra sensors from the chip. This, however, still applies to Socket 7 boards only.

Then manufacturers came with the idea of temperature sensors on cables (which are available for purchase). With Winbond, the first extra sensor can be connected to the CPU, the second to the power supply, or against the chip on the graphics card, or the hard drive, etc. The sensors will report the temperature to the chip, which can be read by software."

The BX6 (and BH6) boards implement the LM79 chip, which means that the CPU temperature cannot be monitored. The Super7 AX59Pro board, implements a Genesys Logic chip (www.genesyslogic.com), which is not supported by MotherBoard Monitor. It comes with its own monitoring utility from AOpen, which does not work under Windows NT. A version downloadable from the Genesys Logic site doesn't either. Thus, for all practical purposes, no fans can be monitored with this board under NT.


System boards should provide two fan connectors for the CPU cooler. Ideally, there should be at least three connectors for case fans. In the absence of standard locations, one should be close to the power supply and at least two should be as close to the drive bays as possible. Fan wires
should be long enough (30-50" preferably) to reach any location on any board. However, since an increase in the the overall case temperature from fan failures is not as critical as that from a CPU fan failure (particularly with overclocking), monitoring the case temperature and less than all fans is acceptable.

In addition to the power supply fan, cases should have at least two additional fans standard. All should, at least optionally, be available with 3-pin connectors. Standard case locations for fans are desirable, such that the location of connectors on the system board can also be standardized.

System board makers should implement chips that allow for monitoring, at the very least, of two temperatures -- CPU and system board -- system voltages and at least two fans (CPU), but preferably more. Chip standardization is desirable.

As things stand, users must take factor complications into account when choosing system boards, cases and cooling/monitoring devices.

* check (a) which monitoring chip and (b) the number and locations of fan connectors implemented by the system board and, all else being equal, prefer one with more fan connectors and the Winbond chip, or at least one which is common and thus supported by monitoring software

* use MotherBoard Monitor, or equivalent software to monitor your system; there are instructions on the Web on how to monitor CPU temperature via the Winbond chip, by installing sensors; without the Winbond chip, you can get a device such as ThermAlarm (www.gsconline.com), that combines a set of user-placeable sensors with its own monitoring software

* order as many fans with 3-pin connectors as the system board supports and the rest with power supply connectors (any excess 3-pin fans you won't be able to connect at all); make sure the wires of the 3-pin ones reach the connectors on the board )

(I would like to thank Alex van Kamm, Vincent Tzeng of Tennmax and Chung Bao of Acadia Technologies for help with this article)

Copyright © 1998 by Fabian Pascal. All Rights Reserved