How to recognise a 3.3 Volt PCI slot?


Typical high-performance PC with two 3.3V/64-bit PCI slots

The image above shows a typical high-performance PC (year 2001) with some 64-bit slots. In the image you can see that there are four 32-bit slots (with the short connector) and two 64-bit slots (with the long connector).

The keying (the little white lines inside the connector) show the I/O signalling type used on the PCI-bus. In this case, the 32-bit slots are 5 Volt slots. The 64-bit slots use in this case 3.3 Volt signalling. In principle also 3.3V/32-bit slots can exist, but this is hardly ever used.  5V/64-bit slots do exist as well in certain machines such as industrial PCs.

A slot that uses a 66 MHz PCI clock, always will use 3.3 Volt signalling. In fact there is no way to see from the connector if a slot is using a 33 MHz clock or a 66 MHz one.


  • What types and how many type of PCI slots are in this PC?



A S32PCI64 card can work only in a 3.3 Volt slot
The S32PCI64 and the FILAR can only work in slots that use 3.3 Volt signalling. That means you should check if indeed the 3.3 Volt key is as shown in the picture above (a key near the panel of the computer). 

The cards will work in 66 MHz and 33 MHz environments and can work in 32-bit and 64-bit slots. So it is only the PCI signalling type of 3.3 Volt that is important to look at. 

Anyway, the S32PCI64 or FILAR will mechanically not fit in 5 Volt slots, so there is no risk of breaking anything.



Be careful when you use a PMC to PCI adapter. These adapters (such as the ones from Technobox) are useful for putting (old) PMC cards from the VMEbus days into PCs. Usually these adapters fit in both 5V and 3.3V slots (i.e. they have a dual voltage keying). If the PMC (such as the.SSP or SPS) plugged on is 5V only, one must of course not put it into a 3.3V slot even though the keying would permit one to do so.

CERN - High Speed Interconnect - S-LINK
Erik van der Bij - 27 March 2002