On PCIe 1.0, does a 64 bits graphic card could be compatible with 32 bits OS (Windows 7 32bits)
The bit width of the bus (PCI, PCI-X, AGP, PCIe, etc) has nothing to do with the processor word size. It is simply the number of bits the communication channel can carry at a time.
The southbridge (now part of the Intel PCH or AMD chipset) handles the communication between the CPU and expansion cards (including video cards), so the bit width of the bus does not create any restrictions on the processor architecture.
Ultimately, whether your system can use the cards attached to your computer's expansion slots comes down to whether appropriate drivers are available.
There are three options here:
The card only has 64 bit drivers (unlikely, though 32bit systems are finally dying and eventually no new software will be written for them. This might take a few more years though).
It is not PCI-e. Joeqwerty's comment about PCI or PCI-X might be on target. PCI comes in 32 bit and in 64 bit flavours. PCI-e comes in lanes.
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The most likely situation: The speed of a graphics card depends mainly on two factors:
- The Graphics chip (the GPU)
- The speed in which the GPU communicates with the on-board memory.
The latter is influenced by the memory speed and by the width of the path to the memory. This width is often 64, 128, 192, 256, 384 or 512 bit.
All of which is unimportant to the OS. The OS just needs the right (32 or 64 bit) driver to match its own setup.