According to this article , the bus is the circuit that connects the motherboard . The faster the speed of the bus , the quicker data can be transferred . Bus speed is measured in MHz (Mega Hertz) and a bus speed of 66 MHZ means that that are 66 million cycles per second . Hertz means how the frequency of x every second
For CPU , 66 MHz means 66 million instructions can be processed every second
How about for Bus ?? How much data is terms of btyes is transferred for every cycle ??
It's the speed at which the PCI protocol operates over the bus. It's the CLK signal in the illustration below.
Wikipedia gives this formula for 32-bit 33MHz PCI, which is x2 for 32-bit 64MHz PCI:
Peak transfer rate of 133 MB/s (133 megabytes per second) for 32-bit bus width (33.33 MHz × 32 bits ÷ 8 bits/byte = 133 MB/s)
There is an address phase and a data phase in the protocol as you can see below, so not all of the 266MBytes/sec will be dedicated to actual work. There is a bit of overhead.
From this:
The basic transfer mechanism is a burst, composed of an address phase and one or more data phases.
Typical read and write transfers are illustrated below:
This article mentions an effective throughput of 90MBytes/sec of the theoretical 133MBytes/sec due to the overhead. For 32-bit 66MHz it would be doubled.
