ทำไม CPU Bus ถึงมีหน่วยไม่เหมือนกัน แล้วเราจะเปรียบเทียบอย่างไรว่าใครเหนือกว่า?

[{Cyberman}]

รุ่นที่ 1 มีค่า CPU Bus = 5GT/s DMI
รุ่นที่ 2 มีค่า CPU Bus = 2600MHz

เราจะแปลงหน่วยให้เป็น Hz เหมือนกันได้อย่างไรเพื่อจะได้นำมาเปรียบเทียบกันได้

[{Cyberman}]

FSB@1600Mhz= 12.8GB/s
QPI@6.4GT/s= 25.6GB/s
DMI@ 2.5 GT/s= 1.25GB/s(effectively 1GB/s due to overhead)

[{Cyberman}]

ยิ่งอ่านก็ยิ่งงง ยิ่งเจอภาษาอังกฤษ ยิ่งไม่เข้าใจ @_@

This is incorrect, it doesn't tell you the amount of data, it tells you the number of transfers per second.

T/s (number of transfers per second) = (clock speed) * (transfers per clock cycle)
For example: 4 GT/s = 1 GHz * 4 transfers per cycle

On Wikipedia, there is a table showing number of transfers per cycles for each family of CPU's.

The calculated amount of data is the "Bit Rate," usually expressed in bit/s or bps. If you know the transfer rate (GT/s), bus size, and overhead due to encoding, you can calculate the effective bit rate:

Bus Size: 8 Bytes
Clock Speed: 100 MHz
Transfers per clock cycle: 4
Encoding: 8b/10b
Gross Bit Rate = 8 B * 100 MHz (cycles/second) * 4/cycle = 3200 MB/s
Effective Bit Rate = (gross bit rate) * (encoding) = 3200 MB/s * 8b/10b = 2560 MB/s

Real-life examples below show how PCI Express bit rates are calculated. Note, I'm showing multiple PCI Express slot lengths (x1, x4, x16) to illustrate how those affect the calculation:

PCIe v1.0 x1:
Bus Size: 1 bit = 1/8 Byte
Baud: 2.5 GT/s = 2500 MT/s
Encoding: 8b/10b
Bit Rate: 250 MB/s = (1/8) * 2500 * (8/10)

PCIe v2.0 x4:
Bus Size: 4 bit = 1/2 Byte
Baud: 5 GT/s
Encoding: 8b/10b
Bit Rate: 2 GB/s = (1/2) * 5 * (8/10)

PCIe v3.0 x16:
Bus Size: 16 bit = 2 Byte
Baud: 8 GT/s = 8000 MT/s
Encoding: 128b/130b
Bit Rate: ~16 GB/s = 15,753 MB/s = 2 * 8000 * (128/130)

You may sometimes see PCIe bit rates listed that are 2x the values shown in these calculations, but those are "aggregate" numbers, meaning they double the number to reflect simultaneous reading and writing.