Adding more devices to PCI slots

Question

Hi all,
My G4 AGP specs tells me my Mac's 3 PCI slots are 64bit, 33mhz. I have two slots available and one slot I added a 4port USB card working great. Just curious but what exactly is 64bit, 33mhz? What does it mean? What can I add to these slots besides another USB card, firewire card, and/or external HDD?
Thanks
Web dude

Answer 1

Hi-
64 bit refers the the memory addressing architecture of the PCI bus. It is of consequence when choosing a PCI card not only for compatibility, but also for enhanced performance characteristics of 64 bit architecture. What the 64 bit PCI bus allows, is sequential read, write, and invalidate (clear)commands to occur in a single operation. This, of course, translates to performance.
33MHz is the clock frequency of the bus, or, more commonly thought of as, the speed of data transfer through the bus. This, when combined with the memory addressing architecture, yields the data rate of the bus.
The theoretical limits of the PCI bus translates to 264 MB/s for 64-bit @ 33MHz or 132 MB/s for 32-bit @ 33MHz.
The 64 bit slots are backwards compatible to 32 bit architecture as well.
PCI cards can have many different duties. External interface bridges such as USB 2.0, FW 400, FW 800 and eSATA are common for PCI expansion.
Hard drive controller cards for both ATA and SATA drives are also common.
Other types of controllers such as SCSI and hardware RAID are available.
Sound cards are also common for PCI expansion.
Video capture, ethernet, wireless, TV tuners, modems, even controllers with a hard drive mounted to the PCI card board are some of the expansion devices that are available.