Bodaggit23
Active Member
The AGP slot is either 4x or 8x faster than the PCI slot.
Can I do this?
- Thread starter JLuchinski
- Start date
That is not quite correct. AGP 1x actually has twice the bandwidth of standard PCI. The 32bit/33MHz standard PCI spec has a maximum bandwidth of 133MB/s. The initial 32bit/66MHz AGP 1x has a maximum bandwidth of 266MB/s throughput. AGP 2x doubles that to 533MB/s. AGP 4x doubles that to over 1GB/s. And, AGP 8x doubles that further to roughly 2.1GB/s of throughput. So, technically the AGP 8x (3.0 spec) is 16x faster than base PCI.
Bandwidth is not the only major difference between AGP and PCI. First, PCI is a bus. All devices on that bus must share that 133MB/s of bandwidth. The AGP slot is, as its name states, a port (Accelerated Graphics Port) not a bus. The AGP card has all that bandwitdh (as shown in the first paragraph) all to itself. AGP also allows for direct access to the CPU and main system memory (DIME - Direct Memory Execute). Direct access to system memory via pipelining and sideband addressing gives AGP a huge edge over PCI in and of itself. Second, AGP chips can make multiple data requests simultaneously per clock cycle whereas PCI chips cannot. PCI only makes one data request per clock cycle.
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AGP was a more or less a port/interconnect, not a bus. It ran off a PCI 2.1 standard/hence 66mhz, but didnt share bandwidth with the PCI bus. Had a direct connection to the system memory unlike the PCI bus that had to go through the northbridge. To get X2,X4, X8 they just X2 or X4 or X8 pumped the clock cycle.
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