Ken,

    According the the specifications of a Dell Precision 650 Workstation, you have the following expansion slots available.

 

Dell Precision 650 computer — Three PCI-X connectors, two PCI slots, and one AGP 8x Pro110 connector

All pci slots are backwards compatible.

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@jjbuckaroo wrote:
All pci slots are backwards compatible.

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I have to disagree with this statement for SEVERAL reasons.

SOME slots not ALL have backwards compatability and only for Universal PCI cards that work 3.3v only.

Some PCI cards REQUIRE 5v.  NOT ALL PCI SLOTS provide 5v.  Some only provide 3.3v.

Some PCI cards need PCI 2.2 spec and some are only PCI 2.1 or worse 2.0 spec.

The PCI Xpress ala X8 X16 etc slots dont have 5v 32 bit backwards compatability.

PCI-Express. This standard is electircal and logical not
backward compatible with PCI / PCI-X.

For example a Motherboard that has an Intel 915 chipset that
has:
1 - x16 PCIe slot
1 - x1 PCIe slot
2 - legacy 32-bit PCI slots

Derived from this parameters, three main PCI bus types are used in common:

32 bit PCI with 5V signal voltage
This is the typical PCI slot found on usual desktop computer mainboards. Clock speed for data transmissions is 33Mhz. Therefore the maximum transmission capacity calculates to 1 gigabit/s.

64 bit PCI with 5V signal voltage
This PCI slot is usually found on dual processor desktop and server mainboards. Clock speed for data transmissions is 33Mhz. Therefore the maximum transmission capacity calculates to 2.1 gigabit/s.

64 bit PCI with 3.3V signal voltage
This PCI slot is found on modern server mainbords. Often you find the term PCI-X in the technical specification. Clock speed for data transmissions varies from 66 Mhz to 533 Mhz. Therefore the maximum transmission capacity calculates to 4.3 gigabit/s using 533 Mhz clock speed. The slots maximum clock speed will be shown a number after PCI-X. An example PCI-X 133.

The following pictures will allow you to identify the different PCI bus types as of the used socket type. The top of each picture represents the backside of the mainboard, e.g. the slot bracket will be placed there if PCI extension card is plugged into the slot. Please note the coding nose near the backside which will identify a 3.3V only slot and prevent a 5V only card from being inserted because this might damage board or card.

Note the Extra Keyways

 

 

The Legacy Slots are for Backwards Compatability.
The documentation for the Chipset and Motherboards say that the x16
slot is PCI-Express compliant. But it also always puts in the note,
"Intended for Graphics."

 

The Peripheral Component Interconnect (PCI) bus standard was adopted to ease the integration of personal computers and peripheral devices. While many engineers have easily installed PCI bus cards, some have found that PCI’s promise of "plug-and-play" cards is just that, others have experienced difficulty integrating PCI bus interface cards with their host computers.
  Many PCI cards and PCs are compatible, but you have no guarantee that your cards will work with your PC. You may find that a card works in one PC but not in another or that your card works only in certain PCI slots on a motherboard. The problems can have many causes, depending on your PCI core-logic chip set, system BIOS, and PC’s motherboard design. Manufacturers of motherboards, PCI core-logic chip, or BIOS programs may not follow the PCI bus specs exactly.

Putting a 32 bit PCI card in the bus can slow down ALL CARDS on the bus in some cases causing performance issues and other problems.

Why do some slots work but not others? Because not all PCI slots are created equal. Some slots may connect to the primary PCI bus, while others connect to a secondary bus through a PCI-to-PCI bridge chip. PCs need a PCI-to-PCI bridge chip to provide enough PCI expansion slots to satisfy most PC users. Because the PCI bus is unterminated, there is a limit to how many loads it can drive. To provide for more PCI devices, motherboard designers add PCI-to-PCI bridges. Motherboards may have two or three PCI expansion slots (but can have from one to four) on the secondary side of a bridge. Slots on the secondary side of a PCI-to-PCI bridge may not function the same as slots on the primary side do.

The OLD GX1 is one of the first I remember having a DEC PCI to PCI Bridge.

PCI- to-PCI bridges work in conjunction with the PC’s BIOS. When your PC boots, the BIOS must recognize the PCI-to-PCI bridge, scan the secondary bus, and configure any devices on that bus. Unfortunately, your BIOS may not fully configure the secondary slots. For example, a BIOS may not have programmed the secondary PCI bus to work with bus master cards. Any BIOS that doesn’t properly configure the devices on a secondary PCI bus isn’t in compliance with PCI specs.

Even if your PCI slots meet the PCI spec, you can still have interrupt problems.