FSB and memory speeds

[Chewdon]

I am putting together a new computer. The mobo supports a P4 with a
533mhz FSB. I got a 2.26 ghz chip and 256 DDR. The manual says that
the board can support memory speeds from 100 to 166mhz. I don't get
it. Is the memory speed the same as the FSB? If the memory speed is
slower then the FSB does that create a bottle neck? Can anybody
please explaine how this works?

 

[kony]

I am putting together a new computer. The mobo supports a P4 with a
533mhz FSB. I got a 2.26 ghz chip and 256 DDR. The manual says that
the board can support memory speeds from 100 to 166mhz. I don't get
it. Is the memory speed the same as the FSB? If the memory speed is
slower then the FSB does that create a bottle neck? Can anybody
please explaine how this works?

The memory speed doesn't necessarily need to be the same speed, but to
put it in perspective:

533MHz FSB of the P4 is actually 133MHz clock rate, on a quad-pumped
bus (4 transfers per clock cycle) so the data rate approaches 4 X 133
= 533.

That 133Mhz clock cycle, taken as a Double Data Rate (DDR) would be 2
X 133 = DDR266 for the memory.

So, using the same clock rate of 133MHz, the P4 runs at 533 but the
memory at 266. That is on a synchronous bus(es) meaning both FSB &
memory bus use the same 133MHz clock rate. If you instead used an
asynchronous bus, you could set the memory clock rate to "+33", so the
FSB would be at 133MHz but the memory bus at 166MHz. Then the
memory'd be at DDR333.


Dave

 

[Chewdon]

The memory speed doesn't necessarily need to be the same speed, but to
put it in perspective:

533MHz FSB of the P4 is actually 133MHz clock rate, on a quad-pumped
bus (4 transfers per clock cycle) so the data rate approaches 4 X 133
= 533.

That 133Mhz clock cycle, taken as a Double Data Rate (DDR) would be 2
X 133 = DDR266 for the memory.

So, using the same clock rate of 133MHz, the P4 runs at 533 but the
memory at 266. That is on a synchronous bus(es) meaning both FSB &
memory bus use the same 133MHz clock rate. If you instead used an
asynchronous bus, you could set the memory clock rate to "+33", so the
FSB would be at 133MHz but the memory bus at 166MHz. Then the
memory'd be at DDR333.


Dave

So if I have my clock set to 133Mhz on a synchronous bus then I am
bottlenecking at 266Mhz?

 

[DaveW]

The DDR memory that you need to use should run at twice the FSB speed, thus
at 266 MHz.

 

[kony]

So if I have my clock set to 133Mhz on a synchronous bus then I am
bottlenecking at 266Mhz?

Sometimes yes... in general there are performance gains where you'd
need them by getting memory throughput as high as it'll (stabily) go,
but like everything else those last few percent gains in performance
will cost a lot more money (for better memory).

On the other hand, there is often some loss of stability with
asynchronous bus settings, so increasing both the FSB and memory bus
is usually the best performance boost, but of course when it comes to
overclocking you are the judge of what's an acceptible risk to
stability and/or time devoted to testing the system.

It would seem you were looking for a good value rather than expensive
performance, else you wouldn't be using the 2.26GHz CPU to begin with,
so I wouldn't worry about it too much, at worst the money saved now
will allow more frequent upgrades, which can keep the average
performance level of the system(s) you use just as high per same
budget in the long run.


Dave

 

[Chewdon]

Sometimes yes... in general there are performance gains where you'd
need them by getting memory throughput as high as it'll (stabily) go,
but like everything else those last few percent gains in performance
will cost a lot more money (for better memory).

On the other hand, there is often some loss of stability with
asynchronous bus settings, so increasing both the FSB and memory bus
is usually the best performance boost, but of course when it comes to
overclocking you are the judge of what's an acceptible risk to
stability and/or time devoted to testing the system.

It would seem you were looking for a good value rather than expensive
performance, else you wouldn't be using the 2.26GHz CPU to begin with,
so I wouldn't worry about it too much, at worst the money saved now
will allow more frequent upgrades, which can keep the average
performance level of the system(s) you use just as high per same
budget in the long run.


Dave

Actually I am building this computer for my uncle. He is not
concerned with speed. If I were going to build one for myself @
2.66Ghz what kind of memory should I use to get the best performance
for playing games?

 

[kony]

Actually I am building this computer for my uncle. He is not
concerned with speed. If I were going to build one for myself @
2.66Ghz what kind of memory should I use to get the best performance
for playing games?

800MHz FSB version of the CPU, two 512MB modules of PC3200 with the
best timings the budget will allow.


Dave