MadSci Network: Computer Science

Re: what is the difference between microprocessor in buses and speed

Date: Tue Oct 14 06:44:15 2003
Posted By: Eric Maass, Director, semiconductors / communication products
Area of science: Computer Science
ID: 1065630968.Cs

Hello, Leila.

Your first question was:
"what is the difference between microprocessor in buses and speed".

Both the speed of the microprocessor and the speed of a bus (there are 
often several different buses in a computer system) are defined in terms 
of clock rates, which are in Megahertz (millions of pulses used as clocked 
signals per second).

Here is a site that gives an overview of how the microprocessor works:

The microprocessor has a speed or clock rate that is generally higher 
than the bus speed or clock rate. Here is an explanation why the 
microprocessor speed is  different from the bus speed, from this website:

"As PC technology grew, eventually the access speed of the memory 
could no longer keep pace with the increased speed of the 

At this point, an I/O [input/output] cache was placed on the microprocessor 
to be a buffer between the external memory on the motherboard and the 
internal processor registers. 

The memory was set to run at a different "side bus" speed which is some 
fraction of the microprocessor speed. 

Therefore when the speed of the microprocessor is set, it is set to some 
multiple of the side bus speed. In the case of a 500Mhz processor and 
100Mhz PC100 capable memory, that multiple is 5. "
You also asked:
"how are speed or buses in 8088 (cpu)and how are in the others."

The 8088 computer came out in 1979, and had a clock speed of about 5 
MHz .  This webpage has a historical perspective and a table with the 
clock rates of  microprocessors over time:

Here is a more recent article discussing microprocessor and bus speeds 
for more modern systems:

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