PC Tweaking Adventures: Overclocking

I was researching the difference between PC2-6400 and PC2-8500 DRAM capabilities, and comparing some prices.  Out of curiosity, I used CPU-Z to check my current Patriot Viper PC2-8500 4Gigs memory sticks.  It was under the “SPD” tab .  To my surprise, it’s reporting as PC2-6400!  I was afraid I might be using for the wrong memory modules.

I searched the forums for a possible explanation, and I found a few.  Apparently this is a common problem.  The CPU-Z FAQ explains it:

The memory theorical bandwidth is computed using the module access time information for the maximal CAS# latency value, included in the SPD area. If the computed bandwidth is lower than the one specified on the memory module, that means that the SPD information on the module is not correctly programmed, or most likely that the bandwidth is not given at the default memory voltage, but at a voltage defined in an extended profile (EPP or XMP).

It’s basically CPU-Z trying to identify the DRAM using the information from my ASUS P5Q Pro motherboard BIOS.  So, the info is not accurate and I’m going to ignore it  Instead, I’m going to use the “Memory” tab to figure out the correct frequencies.

CPU-Z’s memory reported the DRAM’s frequency at 400 Mhz.  Since this is a DDR2 memory, the effective frequency is only at 800 Mhz¹.  It’s not running at its full potential, which is 553 Mhz, or effective 1066 Mhz.

The problem is the motherboard’s default BIOS settings.  Out of the box, the automatic setting has the lowest FSB speed configuration set at 266Mhz.  Also by default, the automatic setting for the DRAM Frequency is determined by the FSB.  In this case, it ended up setting the DRAM frequency at 400 Mhz, which is pretty low.

So what exactly can I do to fix this?

The answer is in overclocking the FSB.  Increasing the FSB frequency for the CPU bumps the DRAM frequency, accordingly.   Without going crazy with the overclock², I found a safe setting.  I took into consideration the apps and games I’m running, the temperature of the components, and stability under load.  I ended up setting the FSB to 417 Mhz and the CPU multiplier to 7.5x.   I pushed the Intel CPU to operate around 3.13 Ghz.  The DRAM frequency is now at about 521 Mhz.  That’s closer to the target 533 Mhz setting.

I use Speed Fan to monitor the temperatures and Orthos Prime to do the CPU/RAM stress test.  The temperatures inside the case are at reasonable numbers.  It also helps that currently it’s winter and the room temperature is at 23°C.

I’ve also thought about overlocking the PCI-E frequency to speed up the video card, but I’m sure it’s not necessary.

My current BIOS setting is set at low voltage.

Obviously this is just a slight overclock.  The problem is I’m not able to push the FSB frequency beyond 417 Mhz.  The BIOS actually tells me my attempt to overclock failed.  In some cases the OS boots, but Orthos stress test would fail.

I’ll have to play around with the voltage settings some more.  My target is to overclock the FSB to at least 425 Mhz, and CPU to 3.5 Ghz.

1. 2 x 400 Mhz = 800 Mhz [↩]
2. which involves increasing CPU and DRAM voltage by a lot [↩]

Tags: cpu, motherboard, RAM, tweak