AGP transfer rate question

[Yohhan]

I was reading up on AGP here: http://www.howstuffworks.com/agp3.htm, and I have a question as to how to calculate the transfer rate of AGP 1.0, AGP 2.0, AGP Pro, etc.

The site explained that AGP 1.0 sends data in 1x mode for 266 MBps xfer rate with a 66 Mhz clock speed, while AGP 2.0 sends in 2x mode for 533 MBps at a 133 mhz clock speed. How are they calculating that? Don't you multiply 8 bits x 66 mhz to get the transfer rate?

Thanks.

 

[AndyHui]

AGP is a 32-bit wide databus operating at 66MHz for AGP1X mode.

32-bits = 4 bytes (32 /8)

4 bytes x 66MHz = 266MB/s

AGP 2X sends on the rising and falling edge of the 66MHz clock signal, so transfers are doubled to 533MB/s.

Both AGP1X and AGP2X are part of the AGP 1.0 Specification.

Please read the FAQ: What is AGP- 1X, 2X, 4X, 8X, 1.0, 2.0?

 

[Yohhan]

Thanks.