RE: basic doubts in PCI

["Hazzah, Karen" <KHazzah@melita.com>]

>2) If three PCI slots are in a system, does each of the
>add on board ( with the PCI device ) will have the config
>space?

Yes. Each PCI device (including motherboard PCI devices) 
has config space.

>4) How does the software distinguish the addresses of ISA and/or PCI ?

Software *doesn't* distinguish between PCI and ISA addresses. Software 
simply issues an IN/OUT instruction (on a x86) or a memory reference, 
and the PCI-ISA bridge chip decides if this address is for a PCI or an 
ISA device. 

That doesn't mean your software will be exactly the same for PCI and 
ISA devices. The code you write to obtain configuration information 
(physical address assigned to card) for a PCI card is very different
than 
for an ISA card. But once your code knows the assigned configuration, 
access to the device is fundamentally the same whether PCI or ISA.

>5) Where does PCI memory space mapped into in system memory ?

That depends on the PCI-host bridge chip. Typically, the bridge on a PC 
maps PCI memory space "directly" into host address space. That is, 
address 0 in PCI memory space is address 0 in host address space, and 
address FFFFFFFF in PCI memory space is address FFFFFFFF in 
host address space. 

Obviously, this could lead to collisions at the lower end of RAM, but
the 
BIOS prevents this by assigning PCI devices addresses at the top of 
address space (FFFFFFFF) and going down.