CPU, chipset and PCI?

  • Thread starter Thread starter esara
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esara

Hi,
below is the artical which I am reading now. I did not understnad this
part

"The chipset speaks to the PCI bus at exactly HALF the
speed/frequency/tact, so that the CPU talks to all PCI devices through
the chipset with HALF the external tact or bus speed."

My questions are these
1) Which chipset is this??
2) Why the CPU need to go first to that chipset in order to tlk the
PCI devices??
3) and why the speed should be 1/2 if the CPU want to talk to the PCI.

http://www.tomshardware.com/motherboard/19980101/busspeed-01.html

thanks a lot.
 
Hi,
below is the artical which I am reading now. I did not understnad this
part

"The chipset speaks to the PCI bus at exactly HALF the
speed/frequency/tact, so that the CPU talks to all PCI devices through
the chipset with HALF the external tact or bus speed."

My questions are these
1) Which chipset is this??
Click to expand...

There are two main chips on the motherboard that effectively tie all the
different parts together, ie. memory, PCI slots, ISA slots, AGP slot, etc.
These two chips are the 'chipset', known as the North Bridge and South
Bridge. They can be made by various people but they are designed to work
together. Popular makers are Intel, VIA, SIS, Nforce etc. For instance an
Aopen board could have an Intel chipset or a VIA chipset, both boards are
made by Aopen but the main two 'control' chips - the chipset - are made by
different people. Its a bit like a Ford car having Michelin or Dunlop tyres.

nice diagram of how the chipset ties the motherboard together here:
http://www.tomshardware.com/motherboard/20020311/sis645dx-01.html
2) Why the CPU need to go first to that chipset in order to talk to the
PCI devices??
Click to expand...

The CPU is in charge and has lots to do. So the CPU asks the chipset to get
the information for it from the PCI cards, while the chipset is running off
with its orders the CPU can be doing something more important.

Looking back at the diagram from the above link you can see that the PCI
slots are connected to the CPU through the chipset. there is no way to
bypass the chipset.

On a related note; looking at the diagram you can see that if direct memory
access (DMA) is given to the drives they can get to the memory without
bothering the CPU, this is generally a good thing as the CPU can get on with
important tasks while information is transferred, instead of going

Drive - chipset - CPU - chipset - memory

it goes

Drive - chipset - memory

Hence DMA enabled = speed
3) and why the speed should be 1/2 if the CPU want to talk to the PCI.
Click to expand...

Not sure on this one, but it could be many factors, CPUs are quick and
getting quicker, PCI is slow and not speeding up anytime soon, so it talks
slowly to the PCI slots so that every bit of information is understood. Also
PCs work in binary, (signal on or off), so dividing by two is easy to do to
a speed. It would be much harder to cut the speed by a third. Why should the
designers make it hard for themselves?
 
Certainly sympathize with your confusion.
That is poorly done piece of work. In English there is no such word as
'tacted'.
The text is old and seems to apply only to his ill defined example.
The point here should be that the mother board generates bus speeds. 33MHz
for the PCI bus, 66 MHz for the AGP bus and 100,133,166 or 200 MHz for the
( system clock) CPU. Since the CPU can go much faster, it has a setable
multiplyer assocated with it so it generates its own clock( CPU speed)
.. The FSB is a bunch of wires connecting the CPU to the North Brigde. The
North Bridge manages the memory. So, the FSB runs at the menory speed.
With a DDR memory scheme that speed is twice the system clock speed. A
system where in the system clock is set at 166MHz and DDR is uaed will
requir a CPU that will run at (166*2) or 333MHz FSB.
JPS
 
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