FSB discussion

This is not a request for help, I'm just trying to understand some things about motherboards.

When my Mom's motherboard and 2400 Duron blew I replaced them both with exact replacements, since XP is so picky about upgrades on computers. It was slow, I didn't realize how slow until after she had passed away and I had a chance to dink with it. I was under the (false) impression that strapping had pretty much gone away on motherboards, and had missed restrapping the FSB on the new MB. I felt like an arse, but she liked the computer, and I was doing my best.

My personal computer has a 2400+ Athlon, but has been showing up on bootup as 1900+. I went back through the manual and found the straps I had missed when I replaced my other (blown) motherboard with a similar but different model (it was close enough the MB drivers worked). Because of the lower speed I had been thinking of replacing the MB with the same one that had blown before (Elite K7S5A), since it was smart enough that BIOS set everything, no straps. The current MB (Elite K7VTA3) has a FSB strap, which when set boosted the CPU speed from 1900+ to 2500+. Everything is stable and works. The specs before and after read something like

FSB 133 166
DRAM 166 166
DRAM Clock 166 166

The slight overclocking is bothersome, but I'm not going to worry too much about it. With folding@home running the CPU temp is 51, it dropped several degrees when I went to BIOS and was studying it, and I have the alarm set for 60 degrees.

So, after all this long windyness, what exactly is Front Speed Buss, and how does it enter into CPU speeds?

 

Cpu Clock Speed = FSB X Multiplier

example:

I have a SD 4000+ whose default clock speed is 2400Mhz
The FSB (not so called on A64 cpus) is 200Mhz
The multi is 12

So

2400=200 x 12

In a XP based system, the FSB basically connects the CPU with the main memory.

Hope this helps

 

My MB shows 2 numbers (3 actually), FSB, DRAM (this is memory), and DRAM CLK. This is not meant to be arguementative, my impression on FSB is it related to the PCI bus somehow.

 

Bill, indeed it is, but risk is also right. FSB, or correctly, front side bus, is CPU to system memory (RAM) data bus- the speed which CPU communicates with RAM. You are correct because it also connects the CPU to the north bridge, which controls PCI bus, AGP bus, and SATA HDDs (these bus speeds are derived from the FSB speed). Think of it as the CPU to north bridge speed. Higher FSB means faster processing speeds (FSB x multiplier = CPU clock speed, as risk points out). Just remember to divide FSB by 4 (clocks per cycle) to get the FSB for the equation for Intel CPU's and by 2 for AMD. This is due to the differing in clocks per cycles. Also note the technically it is not called FSB in AMD, but is referred to as such.

That's why when you overclock by changing FSB, you also OC everything on the north bridge. It would be awesome if processors came with unlocked multipliers, then we could clock without limitations of devices on north bridge.

 

You are correct in your diagnosis Walter with regards to FSB and the northbridge, however i would beg to differ that multiplier adjustment restrictions are more related to your motherboard and its firmware and not the processor itself!


Regards

 

Understanding System Memory and CPU speeds: A layman's guide to the Front Side Bus (FSB)
http://www.directron.com/fsbguide.html

In your system or any socket A for best performance, you want to keep the CPU & Memory FSB at matching speeds
pci at 33, AGP 66

 

Nice link Asus......its been a while since i dug this deep, so thanks for the read!

Regards..

 

It was a good read, basically what I was hoping for. Thanks.

 

The lock is hard-wired into the CPU. You can always lower the multiplier most of the time, but raising it is locked unless it comes unlocked by the manufacturer.

 

Nothin a soldering iron wont fix!... Hehe

I remember the old days when the geeks talked about using nail polish and a silver pen to 'trick fix' the old laser cut athlon chips!
As well as the old 'goldfinger' device for the early athlon.

But i guess your right too mate, as they wire both the processors and the mobo's to restrict our evil intentions.....its mechanical, firmware can do nothing as i should have known!

Regards..

 

Hey nitecrawler. Is it possible to fix today's processors (unlock multipliers)? I would imagine that if it were even remotely easy it would be done more often. I haven't heard of anyone doing that, but I would love to see it done, if possible. I think it is possible, but very difficult. I don't know how, however.

 

I also remember the days of unlocking my tbird 900 with a graphite pencil... only problem with that was that it was temporary.... but i guess that was also a good thing because if you screwed it up it didnt cause any real permanent damage