▮ PCIe Interface Speed Rate
▮ PCIe Concepts
Transfer speed is GT/s, not Gbps, as the transfer contains overhead bits that do not provide any additional performance. For example, PCIe 1. x and PCIe 2. x use an 8B/10B encoding scheme, resulting in 20% (= 2/10) of the original channel bandwidth.
GT/s (gigabit transfers per second): Indicates the number of transfer times per second. The approach is to describe the speed characteristics of the physical layer communication protocol, which can be independent of the width of the link.
Gbps (gigabit bits per second): There is no proportional conversion relationship between GT/S and Gbps.
▮ PCIe Bandwidth Calculation
PCIe throughput (available bandwidth) is calculated as follows:
Throughput = Transmission rate * Encoding scheme
For example, the PCI-E2.0 protocol supports 5.0 GT/s, that is, 5G bits can be transmitted per second on each Lane. This does not mean that every Lane of the PCIe 2.0 protocol supports a 5Gbps rate.
Why do we say that? This is because PCIe 2.0 uses the 8B/10B encoding scheme in the physical layer protocol. This means that 10 bits must be sent for every 8 bits transmitted. The two extra bits are not meaningful information for the upper layer.
Then, each Lane of the PCIe 2.0 protocol supports a rate of 5 * 8/10 = 4 Gbps = 500 MB/s.
Take a PCIe 2.0×8 channel as an example. The available bandwidth of x8 is 4 x8 = 32 Gbps = 4 GB/s.
In a similar way
The PCI-E3.0 protocol supports 8.0 GT/s, which means that each Lane can transmit 8 Gbit /s bits per second.
The physical layer protocol of PCIe 3.0 uses a 128B / 130B encoding scheme. That is, 130 bits need to be sent for every 128 bits transmitted.
Then, each Lane of PCIe 3.0 supports a rate of 8 * 128/130 = 7.877 Gbps = 984.6 MB/s.
A PCIe 3.0 x16 channel, x16 available bandwidth is 7.877 x16 = 126.031 Gbps = 15.754 GB/s.
From this, the data in the above table can be calculated.
▮ Bonus
| Year | Bandwidth | Frequency/Speed |
|---|---|---|
| 1992 | 133MB/s (32-bit simplex) | 33 Mhz (PCI) |
| 1993 | 533MB/s (64-bit simplex) | 66 Mhz (PCI 2.0) |
| 1999 | 1.06GB/s (64-bit simplex) | 133 Mhz (PCI-X) |
| 2002 | 2.13GB/s (64-bit simplex) | 266 Mhz (PCI-X 2.0) |
| 2002 | 8GB/s (x16 duplex) | 2.5 GHz (PCIe 1.x) |
| 2006 | 16GB/s (x16 duplex) | 5.0 GHz (PCIe 2.x) |
| 2010 | 32GB/s (x16 duplex) | 8.0 GHz (PCIe 3.x) |
| 2017 | 64GB/s (x16 duplex) | 16.0 GHz (PCIe 4.0) |
| 2019 | 128GB/s (x16 duplex) | 32.0 GHz (PCIe 5.0) |
END.
