Query about PCI base address registers

Hi, In PCI configuration space there are 6 registers BAR0-5 which can hold the ioaddress or memory address used by card. However my question is - how will we know which BAR register contain ioaddress and which contain memory ? and How many of them contain the addresses. I mean shall we start reading from bar0 to 5 all to find it ? If card has 3 ports and one memory region will it be in bar0 or bar1 or bar2 ? Second is on PCI card we set it as bus master for DMA in probe function and also allocates buffer. So when is DMA actually initiated by it ? Please can anybody clarify. Thanks, -Ulka --