By bluescreenNoob ยท 6 replies
Jun 9, 2003
  1. What does FSB do? I know what it's called but not what it does. I've been curious cause most AMDs I notice are 333 while a lot of the p4s are up to 800.
  2. StormBringer

    StormBringer TS Maniac Posts: 2,244

    Frontside Bus. I/O buses, which connect the CPU with the systems other components
  3. Steg

    Steg TS Rookie Posts: 269

    yes it is exceddingly odd that - a P4 3.06 Ghz 800Mhz FSB doesnt perform a huge amount faster than a XP 3000+ 333 FSB dispite having a much faster clock & FSB speed - odd or what?

  4. Justin

    Justin TS Rookie Posts: 942

    The reason is that the "333" and "800" mhz is total BS. It's what we call, "Marketing Megahertz."

    The ACTUAL frontside bus speed of a "333mhz" bus athlon system is 166mhz. The ACTUAL frontside bus speed of an "800mhz" bus p4 system is 200mhz.

    Same goes for 266/533/400/etc. What these architectures do is use methods similair to DDR to achieve higher throughput using the same amount of cycles - more work per cycle. If, say, using one method, you can transmit 1 gig of data per second @ 133mhz, but then discover a way to transmit 2 gigs of data per second @ 133mhz... it's the same as if your first method was @ 266mhz.

    One of the numerous reasons a p4 doesn't scream ahead like the numbers say it should is that the transfer rate of a supposed "800mhz" is a perfect-world scenario: You never actually achieve throughputs that high and typically never even approach the limits; other components prove to be bottlenecks beforehand.
  5. Justin

    Justin TS Rookie Posts: 942

    Technically the FSB is *not* an I/O bus. It handles I/O only between memory and CPU, as well as handling ISR requests via the PIC. The southbridge (PCI bus) is the I/O bus, pretty much any device other then the cpu will go through the southbridge to access memory. The FSB is more of a "Traffic controller" then anything.

    It's really an amazing thing, the way it works, if you get really into it. You can look at brand new motherboards, things produced just months ago.. and look at the technology which is approaching three decades in age.

    Bluescreennoob: The primary function of the FSB is, as mentioned above, the memory controller half of your chipset. It is perhaps the second most important component, as it (not as much anymore, but it used to) dictates the operating speed of every other bus on the system. Back in the golden olden days, ALL devices ran at the same speed as the same FSB, even the cpu.

    A secondary function of the FSB (although you can sort of say this is just an addition from time) is to handle ISR. When a device requests CPU time, it generates an interrupt service request (ISR) via an IRQ (not so much today, but in the old days, an IRQ was actually one physical wire on the system... you would jumper a device to use one physical line that represented, say, IRQ 7). Now while the CPU can recognize that a device needs CPU time to process some data, the CPU doesn't know WHAT to do. The PIC has a table of functions, which translate the request to a cpu function.
  6. XtR-X

    XtR-X TS Rookie Posts: 863

    May be a little off topic but, FYI, there are no 3.06GHz Pentium 4 processors at 800FSB, they are at 533FSB. 3.0GHz is at 800FSB.

    Well, at least right now cuz technology never stops.

    The reason that there 800FSB is out because it's quad pumped. We haven't aquired the technology to produce a 800FSB processer single pumped---yet.
  7. Abraxas

    Abraxas TS Rookie Posts: 157

    Do you know? ;)
    I'm a supporter of the theory that advanced technology - or at least finished schemes - lies hidden in someones storage. :D
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