troubleshooting Question

Advice needed on CPU-Motherboard compatibility

Avatar of BillDL
BillDLFlag for United Kingdom of Great Britain and Northern Ireland asked on
4 Comments1 Solution4402 ViewsLast Modified:
Hello Experts

I bought an old PIII Slot 1 CPU from ebay for absolute buttons.  I wanted to upgrade an old system that I use for testing out installations on, but I have now notices a mismatch that probably means that I can't use the CPU in the board. The postage was double what I paid, and that was just as it really cost to post a local package, so it's not going to break the bank if I can't use it.

My current system:

SuperMicro P6SBA Slot 1 (SECC2) motherboard Revision 2.00 Model ST371313 04/99. Based on Intel 82440BX Revision 3.
Motherboard ID (from AIDA32):
62-0101-006389-00101111-071595-440BX/GX$0AAMH301 1121001130 SUPER P6SBA Motherboard BI

It doesn't show what I recognise as a standard BIOS String at POST, but just a section of the Motherboard ID above, ie. 1121001130 SUPER P6SBA Rev. 3.1.
I believe this is the "Date Code".  See page 68 of the manual:

Pentium III 450 MHz sSpec SL35D
Katmai 0.25 Micron technology
Stepping kC0
Core Voltage 2.00 -> 2.05 Volt <----------- ** NOTE **
I/O Voltage 3.3/2.9  Volt
Bus Speed: 100 MHz <------------------- ** NOTE **
Bus/Core ratio 4.5 (ie. 100 MHz x 4.5 = 450 MHz)

AMIBIOS: Sticker A719312 SBA1192
BIOS Date: 01/15/99
BIOS ID (from AMIBIOS ID Utility):   62-0101-006389-00101111-071595-440BX/GX

The new Pentium III CPU I bought has the following specification:

sSpec Number: SL3XN  
Frequency: 733 MHz
Core Voltage: 1.650 <---------- ** NOTE ** (quoted in other references as 1.7 Volt)
Bus Speed: 133 MHz <--------- ** NOTE **
Bus/Core Ratio: 5.5 (ie. 133 MHz x 5.5 = 731.5 MHz)
Core Stepping: cB0
Coppermine Technology: 0.18 micron
(No mention of I/O Voltage in that Intel spec).

The important point here is the Core Voltage.  The Coppermine (0.18 Micron) Pentium III CPU's have a Core Voltage of 1.65 or 1.7 Volt, while the older Katmai (0.25 Micron) ones have a Core Voltage of 2.0 or 2.05 Volts.  The differences are due to different "stepping" versions in this "family" as the technolgy changed during the manufacturing period quite a lot.

The core voltage for the 450, 500 and 550 MHz Slot 1 Pentium III CPU's is 2.05 volts for the stepping models: kB0, kC0, and is the same for 600 and 600B MHz stepping kC0 models. (My 450 MHz version is kC0).

For stepping models cA2, cB0 in speeds 533EB, 550E, 600E, 600EB, 650, 667, 700, 733, 750, 800, 800EB, 850, and 866, the core voltage is 1.65 Volts (My new 733 MHz version is cB0).

As far as the motherboard goes, setting the Core/Bus Ratio is done from jumpers (JB 1 to 4) that allow the range between x3.0 to x7.5 (x8.0 for the later Revision 4.0 board).
Bus Speed Selection by jumpers (JP 11) only offers up to the Motherboard's limitation (ie. 66 MHz or 100 MHz), but also has an "Auto" setting which states that speed is "Determined by the CPU".
Pages 25 and 47 of the manual below.
P6SBA Model layout Page 25.
Common motherbard family features Page 29.

From Page 33:
"Auto-Switching Voltage Regulator for the CPU Core
The switching voltage regulator for the CPU core can support up to 20A
current, with the auto-sensing voltage ID ranging from 1.4V to 3.5V. This
will allow the regulator to run cooler and thus make the system more stable".

From Pages 3 and 29:
"Currently, the P6SBA motherboard supports CPU speeds up to 1GHz with 100 MHz FSB speed".

CMOS Setup starts on page 68. Nothing aparently relevant except on page 88, ie. CPU Temperature threshold alarms.  Currently set at failsafe.

BIOS Update:
Readme docs in download give no indication of version history.

OK, so hopefully that gives sufficient detail of the setup and allows you to provide me with the best advice, so here's what I am asking:

1. What is likely to happen if I set the Bus Speed jumper (J11) to "Auto" and set the Core/Bus Ratio jumpers (JB 1 to 4) to 5.5 (ie. 133 MHz x 5.5) and boot to the 733 MHz CPU with the lower Core Voltage (ie. 1.65 v rather than the previous CPU's 2.0 v)?

2. Would it be better if I set the Bus Speed Jumper to 100 MHz and the Core/Bus Ratio to x7.0 or x7.5 (ie. 100 MHz x 7.5)?

3. What is the significance of the "I/O Voltage 3.3/2.9  Volt" statement in the spec for the old processor on the Intel sSpec Finder page and the statement from the motherboard's pdf manual on Page 33:
"The auto-switching voltage regulator for the CPU core can support up to 20A
current, with the auto-sensing voltage ID ranging from 1.4V to 3.5V. This
will allow the regulator to run cooler and thus make the system more stable"?

Does this mean that the processor will only draw what it needs to run on, and the 2.0 Volt Core Voltage demanded by the older 450 MHz CPU is insignificant?

Hopefully you can shed some light on these factors so I can run this sentimental old base unit at a more respectable speed without it overheating and burning up.  Hardware at this level isn't really my forté, fixing software problems is :-)


Our community of experts have been thoroughly vetted for their expertise and industry experience.

Log in to continue reading
Become an EE member today7-DAY FREE TRIAL
Members can start a 7-Day Free trial then enjoy unlimited access to the platform for $9.99/mo
View membership options
Unlock 1 Answer and 4 Comments.
Learn why we charge membership fees
We get it - no one likes a content blocker. Take one extra minute and find out why we block content.
See how we're fighting big data
The Value of Experts Exchange in My Daily IT Life

Experts Exchange (EE) has become my company's go-to resource to get answers. I've used EE to make decisions, solve problems and even save customers. OutagesIO has been a challenging project and... Keep reading >>


Owner of Outages.IO
Phoenix, Arizona, United States
Member Since 2016
Join a full scale community that combines the best parts of other tools into one platform.
Unlock 1 Answer and 4 Comments.
View membership options
“All of life is about relationships, and EE has made a virtual community a real community. It lifts everyone's boat.”
William Peck

Member since 2004