Explanation of bus size, speed ect..

[yankees230230]

Hey Ive been looking but can't seem to find anything on it... can someone link me to or please explain what the differance between bus width like 16 bit, bus speed like 66mhz or bus speed lik 50mb/s.. Are these all somehow related? Thanks for your help!

 

[montag451]

Hi,
the bus width is, how many bits of data can be passed at any one time on a bus [group of wires]
Bus speed is how fast those bits of data can be transferred over the Front Side Bus [FSB] which applies to where your devices are on your motherboard. - The more devices you have, the less 'bandwidth' each device will have on the FSB.
Bus Speed [Mb/s] is the actual or theoretical transfer speed.
for instance, ATA133/UDMA133 have a theoretical maximum of 133Mb/s, but in practice you would be lucky to get over 100Mb/s

 

[yankees230230]

ok so say i have a 64 bit width bus.. that means 8bytes a cycle.. and say it runns at 66mhz .. would it be correct to say theoretically it should have 582mb/s speed... (8x66)

 

[montag451]

in theory ;-)

 

[Calin]

I think 528MB/s would be a better calculation... However, some of the bandwidth is lost on arbitration. Here a point-to-point bus would do better (no arbitration required).
This is the case of the Pentium !!! and Pentium 4 processors - all the processors share the same bus to the chipset (to memory, devices and so on). The Athlon MP had each a connection to the chipset, so in multiprocessor situation they were advantaged.
The Opteron is also using a similar schema (with Hypertransport links). Hypertransport links could be used to connect a processor to a chipset or a processor to another processor, unlike the bus on older processors that could be used only for a processor-chipset connection