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Please help: Can't boot after BIOS setting change

Last response: in Motherboards
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January 9, 2009 3:47:27 AM

Hi,

I have Pentium 4 CPU 2.4 GHz, with 800 MHz FSB
The mobo is D875PBZ (http://support.intel.com/support/motherboards/desktop/D...)
RAM is DDR 400


I was trying to figure out why system memory speed in BIOS is 266 MHz.
I found the following BIOS settings in

Advanced --> Chipset Config --> Memory
SDRAM Timing Cntrl [Manual - User Defined]
CRC Override [Auto]
SDRAM Frequency [266 MHz]
...and other numbers for the memory

I thought that since the PC came with manually overriden clock speed of 266 MHz for memory, I wanted to see if setting it to Auto would clock the memory at 400 Mhz (effective)

So I changed the SDRAM Timing Cntrl to [Auto], and pressed F10 (save and exit).
Since then screen went blank, and I can't boot (tried multiple times)

Please help. What should I do?

Thanks,
January 9, 2009 1:16:58 PM

Find the CMOS reset jumper sometimes labeled CLR-RTC. If you have your motherboard manual look in the jumpers section and it will show you the location. If not it shouldn't be too hard to find as it will be 3 pins on your motherboard, two of them covered with a jumper cap. It will be near to your motherboard battery and will be labelled.
You need to move the jumper cap over one pin so that the previosly exposed pin an the centre one is covered and then leave this for 10 seconds. This will re-set all your BIOS values to their default settings. Move the cap back to its original position and you should be good to go.
January 9, 2009 4:51:01 PM

Thanks. I will try that.
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January 10, 2009 8:27:54 AM

Thanks for the help.
I set the BIOS jumper for my mobo (D875PBZ) in "configure mode" and powered on, thereby forcing it to enter BIOS.
It looks like this mobo has issues with setting the timings by "Auto" mode and letting it get the values from SPD. It doesn't even POST.
I forced the BIOS memory timing setting back to "Manual - User Defined".
But this time, I set the timings according to SPD, i.e., 3-3-3-8, then put the jumper back in "normal mode" and powered on, and it booted. So far so good.
I don't know why my friend (who gave me the old PC), or his vendor, had set it manually to 2-4-4-8 with 266MHz (effective).

(One thing I learnt though from the datasheet of Elpida Chips EDD2508AETA making up my Kingston Value RAM KVR400x64C3A/512 is that it can support a tCL of 2 at 133MHz (effective 266, as was set earlier in my BIOS), and a tCL of 3 at 200 MHz (effective 400MHz) and a tCL of 2.5 at 166 MHz (effective 333 MHz)

After knowing how to come back to 'working' settings, I found out on (http://www.anandtech.com/memory/showdoc.aspx?i=2392&p=5 ) that I could run this RAM even at 2.5-3-3-6 at 400 MHz. So I am doing that right now. So far so good again.

I know that for a given frequency, lesser the timings, the better.
But just out of curiosity, which one of these is better?
3-3-3-8 at 400 Mhz
OR
2-4-4-8 at 266 MHz?

(I know probably for a non-gamer like me, the difference in performance won't be noticeable, but neverthless, which setting is better?)

Thanks a lot again for your help.
a b } Memory
a b V Motherboard
January 10, 2009 9:47:33 AM

Since your CPU runs at 400mhz FSB, I would go out on a limb, without seeing any benchmarks and say that the 400mhz setting would probably net you better overall memory performance.. The speed set at 2-4-4-8 and 266mhz might "feel" faster just clicking around in Windows, but programs that use a little more memory will benefit from the wider bandwidth running at 400mhz more than the quicker timings.
But, as you said, you will likely, actually, never notice the difference one way or another.
!