PCIe data peak bandwidth and effective bandwidth calculation

recently, the bandwidth concept and calculation of PCIe are somewhat blurred, and most of the online search data is a mold, This is calculated by the following formula:

Parallel bus bandwidth (MB/s) = parallel bus clock frequency (MHz) * Parallel bus bit width (BIT/8 = B) * Transmission of several sets of data per clock (cycle)

In particular, after the calculation is not very easy to understand, and then after consulting the information, the following understanding of "personal humble opinion, Welcome message query":

first we need to clarify some concepts :

1. For PCIe, the bus frequency, such as 1.25GHz, 2.5GHz, is generally at the reference frequency of about one MHz, through the PLL achieved

2. Peak bandwidth = Bus frequency x Data bit width x2 (gt/s)

3. Effective Bandwidth = Peak Bandwidth * Encoding method (8/10) or (128/130)

4. GT/S: The number of bits per second on the physical channel that is gbps,mbps = gbps/(8x1000)

For one-way channels:

GEN1X1:
Peak bandwidth = 1.25G x 1 x 2 = 2.5 gt/s = 2.5 Gbps
Effective bandwidth = 2.5 X (8/10) = 2 Gbps = 250mb/s


GEN2X1:
Peak bandwidth = 2.5G x 1 x 2 = 5 gt/s = 5 Gbps
Effective bandwidth = 5 X (8/10) = 4 Gbps = 500mb/s


GEN2X8:
Peak bandwidth = 2.5G x 8 x 2 = (gt/s) = + Gbps
Effective bandwidth = (GT/S) x (8/10) = Gbps = 4000mb/s

gen3x1

Peak bandwidth = 4G x 1 x 2 = 8(gt/s) = 8 Gbps

Effective bandwidth = 8 Gbps x (128/130) = 7.9 Gbps = 984.6 mb/s

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PCIe data peak bandwidth and effective bandwidth calculation