[Linux Basics] PCI bandwidth computing?

 

A bus is a set of signal lines that interconnect and transmit information (commands, data, and addresses. The main parameters are:Bus Bit Width,Bus clock frequencyAndBus transmission rate.

※The bus Bit Width determines the amount of information transmitted between the input and output devices at a time, expressed in bits, for example, the bus width is 8-bit, 16-bit, 32-bit, and 64-bit.

※Bus clock frequency is the operating frequency of the bus, expressed in MHz.

※The bus transmission rate is the maximum number of bytes that can be transferred per second on the bus. Bus transmission rate is calculated by bus width and bus clock frequency.

1. parallel bus.

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

● The PCI bus bit width is 32 bits, and the bus frequency is 33 MHz. Each clock transmits a set of data. Its bandwidth is 127.2 Mb/s, that is, 1017.6 Mbps.

● The PCI 2.1 bus bit width is 64-bit, and the bus frequency is 66 MHz. Each clock transmits a set of data. Its bandwidth is 508.6 Mb/s, that is, 4068.8 Mbps.

● The AGP bus bit width is 32 bits, and the bus frequency is 66 MHz. Each clock transmits a set of data. Its bandwidth is 254.3 Mb/s, that is, 2034.4 Mbps.

● The bus Bit Width of The AGP pro is 32 bits, and the bus frequency is 66 MHz. Each clock transmits a set of data. Its bandwidth is 254.3 Mb/s, that is, 2034.4 Mbps.

The AGP pro is an improved version of AGP, which enables the workstation-level motherboard to use the accelerated performance of AGP to reduce the voltage supply required by the AGP, and there is no major change.

● The AGP 2x bus bandwidth is 32 bits and the bus frequency is 66 MHz. Two groups of data are transmitted per clock. The bandwidth is 508.6 Mb/s, that is, 4068.8 Mbps.

● The bandwidth of the AGP 4x bus is 32 bits and the bus frequency is 66 MHz. Four groups of data are transmitted per clock. The bandwidth is 1017.3 Mb/s, that is, 8138.4 Mbps.

● The bus bandwidth of AGP 8x is 32 bits and the bus frequency is 66 MHz. Eight groups of data are transmitted per clock. The bandwidth is 2034.6 Mb/s, that is, 16276.8 Mbps.

Below:

○ The ISA bus is 16-bit in width and the bus frequency is 8.3 MHz. Each clock transmits a set of data. Its bandwidth is 15.9 Mb/s, that is, 127.2 Mbps.

○ The eisa bus is 32-bit in width and the bus frequency is 8.3 MHz. Each clock transmits a set of data. Its bandwidth is 31.8 Mb/s, that is, 254.4 Mbps.

 

Ii. Serial Bus.

Well, it should be the latest PCI Express. What is different from the preceding parallel bus is that PCI Express belongs to the serial bus, and the concept of bus bandwidth and bus clock frequency is exactly the same as that of the parallel bus, it only changes the concept of bus bit width in the traditional sense. The serial bus uses multiple pipelines (or channels) to achieve higher speed. pipelines are independent of each other and multiple pipelines form a bus system. Such as PCI Express X1, PCI Express X2, and PCI Express x16.

The PCI Express bus frequency is 2500 MHz, which is achieved at a benchmark frequency of 100 MHz through the phase-locked oscillator (Phase Lock Loop, PLL.

Serial bus bandwidth (MB/S) = serial bus clock frequency (MHz) * serial bus bit width (bit/8 = B) * serial bus Pipeline * encoding mode * several sets of data transmitted per clock (cycle)

◆ The PCI Express X1 bus has one bit in width, a bus frequency of 2500 MHz, and a serial bus line with two sets of data transmitted per clock. The encoding method is 8B/10B, the bandwidth is 476.84 Mb/s, that is, 3814.7 Mbps. (The bandwidth is 3.75 times that of PCI .)

The formula is 2500000000 (HZ) * 1/8 (BIT) * 1 (line) * 8/10 (BIT) * 2 (two groups of data are transmitted per clock) = 500000000 B/S = 476.8371582 Mb/s, that is, 3814.6972656 Mbps.

The bandwidth of other types of combinations is shown below.

◆ The bandwidth of PCI Express X2 is 953.68 Mb/s, that is, 7629.4 Mbps. (This mode is only used for internal interface of the motherboard, not for Slot Mode)

◆ The bandwidth of PCI Express X4 is 1907.36 Mb/s, that is, 15258.9 Mbps.

◆ The PCI Express X8 bandwidth is 3814.72 Mb/s, that is, 30517.8 Mbps.

◆ The PCI Express x16 bandwidth is 7629.44 Mb/s, that is, 61035.5 Mbps. (The bandwidth is 3.75 times that of the AGP 8x .)

◆ The bandwidth of PCI Express x32 is 15258.88 Mb/s, that is, 122071 Mbps.

Because PCI-E is a serial interface and data is transmitted in two directions, the data transmission bandwidth is twice the bus bandwidth, that is, the data transmission bandwidth of PCI-e 1.1 x16 = 7629.44 Mbit/s * 2 = 15.6 g/s

PCI-e 2.0 increases the speed of the bus to x32, and its data transmission bandwidth = 15.6g/S * 2 = 31.2 g/s

The unit of capacity is measured in binary or decimal format. The measured value in decimal format is 16 GB/s and 32 GB/s.

 

Some may feel that the bandwidth data here is smaller than the value seen elsewhere, because I recorded actual data rather than document data. Just like 160 GB of hard disk, but only about 153 GB of hard disk can be used.

If you are interested, go on to the next step!

PCI bandwidth is often quoted as 132 Mbit/s. This is the document data, and its actual bandwidth is 127.2 Mbit/s.

This difference is caused:

1. Different reference values of the operating frequency.

2. The unit of capacity is measured in binary or decimal format. 132 MB/second is measured in decimal format, and 127.2 MB/second is measured in binary format.

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

B/S = Hz * bytes * cycle

MB/S = MHz * bytes * cycle

132 MB/second:

The operating frequency of PCI is 33 MHz, that is, 33 MHz * 1000000 = 33000000Hz.

The Bit Width of PCI is 32 bits, that is, 4 bytes.

PCI transmits 1 group of data per clock.

33000000Hz * 4 bytes * 1 cycle = 132000000 byte/s divided by the 6th power of 10 (the capacity is measured in decimal) = 132 megabyte/S = 132 MB/S

And 127.2 Mbit/s:

The operating frequency of PCI is expressed as 30ns. The reciprocal * 1000 = y MHz of x ns, that is, the reciprocal * 1000 = 33.333333 MHz of 30 NS, and 33.333333 MHz * 1000000 = 33333333Hz.

The Bit Width of PCI is 32 bits, that is, 4 bytes.

PCI transmits 1 group of data per clock.

33333333Hz * 4 bytes * 1 cycle = 133333332 byte/s divided by the power of 20 (the capacity is measured in binary) = 127.1566 mebibyte/S = 127.2 Mb/s = 1017.6 MB/

PCI is a local bus launched by Intel in 1991. In terms of structure, PCI is a level-1 bus inserted between the CPU and the original system bus. A bridge circuit is used to manage this layer, it also implements interfaces between upstream and downstream to coordinate data transmission. The manager provides signal buffering to support 10 peripherals and maintain high performance at high clock frequencies. It provides connection interfaces for devices such as video cards, sound cards, NICS, and modem, it operates at 33 MHz/66 MHz.

 

The earliest proposal of the PCI bus worked at 33 MHz and the transmission bandwidth reached 133 Mb/s (33 MHz x 32 bit/8), basically meeting the development needs of the processor at that time. With higher performance requirements, 64-bit PCI bus was proposed in 1993, and later the frequency of PCI bus was increased to 66 MHz.

PCI standard from V1.0 to the current v2.2 v2.3, has been replaced by the PCI-E.

 

Appendix:

1 Qianhe	KHz	103Hz	1 000Hz
1 MHz	MHz	106Hz	1 000Hz
1 Gekhla	GHz	109Hz	1 000 000Hz
1 Taihe	THz	1012Hz	1 000 000 000Hz
1 Pathe	Phz	1015Hz	1 000 000 000 000Hz
1 Aihe	Ehz	1018Hz	1 000 000 000 000 000Hz