Confused at memory bus speeds

[Mahogeny]

I have tried reading several posts on memory bus speeds and I thought I had a handle on them, but after some recent overclocking experience I am not so sure I understand now.

I have a P4 Celeron 2.0Ghz CPU, 2 modules of Kingston PC2100 CAS 2.5 256Mb, Albatron PX845E Pro II motherboard.

Okay, so I understand that PC2100 DDR RAM actually supports running at 133Mhz x 2 = 266Mhz, the P4 Celery only supports FSB of 400Mhz (100Mhz x 4?), and the Albatron mobo supports up to 533Mhz FSB (133 x 4?).

Alright, so I am using locking on the AGP/PCI buses to leave them at 66/33 respectively. When I booted up the system after installing the components my BIOS said that the memory was running at 266Mhz. Okay, so I left the memory alone at first (locked it in the BIOS so that it would remain running at 266Mhz)and overclocked the CPU by a 1.33 factor (from 2.0 to 2.66Ghz). Ran fine without any problems or extra heat. Next, I found that I was easily able to overclock my memory by 33% (from 266Mhz to 354Mhz) however, if I go much higher than this I start having problems.

Now, my question is this - now is my memory really only running at its full speed? If so, then what really is the speed - 133 x 2 or something else? If it is only now running at its maximum speed, then what was it running at before - just 200Mhz (100 x 2)?

I guess you could say I'm just a little bit confused as I was expecting to only be able to overclock the RAM to no more than 140 (or 150 at the very most) x 2 = 280 or 300 at most according to overclocking forums I had looked at...

With my BIOS stating that my memory is running at 354Mhz then that would be considered to be "177 x 2" according to these other forums I visited, which doesn't make sense...

Anyway, sorry for the long post - my wordiness is genetic I guess.

Anyone have any ideas as to actually what is happening on my system and what the "real" speeds are likely at for my CPU, RAM, and FSB?

Thanks,
Mahogeny

 

[bum_jcrules]

"Now, my question is this - now is my memory really only running at its full speed? If so, then what really is the speed - 133 x 2 or something else? If it is only now running at its maximum speed, then what was it running at before - just 200Mhz (100 x 2)?"

Full speed of PC2100 is a base clock of 133Mhz. (400/3MHz to be exact.) It is DDR whis is Double Data Rate. Because the memory sends two bits of information on one signal wave. One on the rising edge and one on the falling edge. SDR is Single Data Rate and only had one bit which is on the rising edge of the wave.

The base clock speed is 133MHz, but with two bits per clock it acts like SDR at 266MHz.

Got it?


I've seen Micron/Crucial handle a lot but that number you have seem to be a lot. Are you sure it is PC2100 and not PC2700? Because going from 166MHz (500/3) to 177MHz makes more sense. If your memory is able to handle that 177MHz base clock speed and it is PC2100, more power to you.

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[Mahogeny]

Yeah, I was starting to think the same thing, but the package said it was PC2100... I think I will download that .zip file that is discussed in this forum that tells you what kind of memory you really have...

Thanks again.

Mahogeny